Anatomical terminology



Study material Diploma in optometrySyllabus for 1st yearTopics:General anatomy and physiologyOcular anatomyOcular pathologyPhysical opticsPrism & LensesRadioscopy & Refraction TechniqueTranspositionRefractive ErrorTopic-1. General anatomy and physiologyIntroduction of anatomyOrganization of body cells tissues, organ systemsCardio vascular systemMusculo skeletal systemDigestive systemExcretory systemNervous systemReproductive systemStudy of anatomy and branches of anatomy The branch of science concerned with the bodily structure of humans, animals, and other living organisms, especially as revealed by dissection and the separation of parts.Branches of Human Anatomy:Human anatomy is divided into following important branches;Gross anatomy is the study of macroscopic details of human body structure. Because gross anatomy is concerned only with macroscopic details, therefore it does not require the aid of any instrument. Generally gross anatomy is studied on dead bodies because you cannot dissect a living human just to study anatomy; therefore gross anatomy is also known as cadaveric anatomy. There are two approaches to study gross anatomy: Systemic Approach and Regional Approach. In systemic approach, human body is studied in different systems and in regional approach, human body is studied in different regions. The end result of both approaches is the same but generally for students of surgery, regional approach is preferred.In contrast to the cadaveric anatomy, in living anatomy deals with the study of live human beings and not dead bodies, therefore methods like dissection cannot be applied. Techniques to study living anatomy include palpation, percussion, auscultation etc.Embryology is also known as developmental anatomy. It is concerned with the study of development of an embryo from a single cell to a complete human being. Embryology provides details of the prenatal and postnatal developmental changes in the body and the mechanisms by which these changes occur.Histology is also known as microscopic anatomy. It deals with the study of microscopic details of tissues that make human body.For detailed study of histology, Surface anatomy, as the named indicates, is anatomy of the surface of human body structures. It is also known as topographic anatomy. Surface anatomy establishes a relation between the internal structures of human body with its surface. It enables a medical professional to locate the position of internal organs from surface of the body and therefore it is very important for surgical operations. Sometimes surface anatomy is described as a sub-branch of gross anatomy but it is better to write it separately to highlight its importance.Clinical anatomy is the application of anatomical knowledge to clinical practice. This branch is a more practical aspect of human anatomy and is of supreme importance for medical professionals.Introduction of anatomynatomy is the science of the structure of the body. When used without qualification, the term is applied usually to human anatomy. The word is derived indirectly from the Greek anatome, a term built from ana, meaning "up," and tome, meaning "a cutting" (compare the words tome, microtome, and epitome). From an etymological point of view, the term" dissection" (dis-, meaning" asunder, " and secare, meaning "to cut") is the Latin equivalent of the Greek anatome.Anatomy, wrote Vesalius in the preface to his De Fabrica (1543), "should rightly be regarded as the firm foundation of the whole art of medicine and its essential preliminary." Moreover, the study of anatomy introduces the student to the greater part of medical terminology.Anatomy "is to physiology as geography is to history" (Femel); that is, it provides the setting for the events. Although the primary concern of anatomy is with structure, structure and function should be considered together. Moreover, by means of surface and radiological anatomy, emphasis should be placed on the anatomy of the living body. As Whitnall expressed it, "I cannot put before you too strongly the value and interest of this rather neglected [surface] aspect of anatomy. Many a student first realizes its importance only when brought to the bedside or the operating table of his patient, when the first thing he is faced with is the last and least he has considered." The classical methods of physical examination of the body and the use of some of the various "-scopes," e.g., the stethoscope and the ophthalmoscope, should be included. Radiological studies facilitate achievement of "an understanding of the fluid character of anatomy and physiology of the living" (A.E. Barclay), and the importance of variation should be kept in mind.In relation to the size of the parts studied, anatomy is usually divided into (1) macroscopic or gross anatomy, and (2) microscopic anatomy or histology (now used synonymously). In addition, embryology is the study of the embryo and the fetus, that is, the study of prenatal development, whereas the study of congenital malformations is known as teratology.In general, works dealing with human anatomy are arranged either (1) systemically, that is, according to the various systems of the body (skeletal, muscular, digestive, etc.) or (2) regionally, that is, according to the natural, main subdivisions of the body (head and neck, upper limb, thorax, etc.). In this book, after the general features of certain systems have been discussed in introductory chapters, the remainder of the work will general follow a regional approach. The regional plan has been adopted chiefly because the vast majority of laboratory courses in human anatomy are based on regional dissection.Anatomical terminologyA discussion of etymology?of many of the common terms used in anatomy is included in this online text. However, the following etymological works are recommended:Field, E. J., and Harrison, R. J., Anatomical Terms: Their Origin and Derivation, 3rd ed., Heffer, Cambridge, 1968.Skinner, H. A., The Origin of Medical Terms, 2nd ed., Williams & Wilkins, Baltimore, 1961.International agreement has been reached on an English and Latin nomenclature, the Terminologia Anatomica. A revision of this terminology is used in this book. Eponyms are avoided except where so common in clinical practice as to be considered essential for the medical student.Terms of position and direction All descriptions in human anatomy are expressed in relation to the anatomical position, a convention whereby the body is erect, with the head, eyes, and toes directed forward and the upper limbs by the side and held so that the palms of the hands face forward. There is no implication that the anatomical position is one of rest. It is often necessary, however, to describe the position of the viscera also in the recumbent posture, because this is a posture in which patients are frequently examined clinically.The median plane is an imaginary vertical plane of section that passes longitudinally through the body and divides it into right and left halves. The median plane intersects the surface of the front and back of the body at what are called the anterior and posterior me dian lines. It is a common error, however, to refer to the" midline" when the median plane is meant.Any vertical plane through the body that is parallel with the median plane is called a sagittal plane. The sagittal planes are named after the sagittal suture of the skull, to which they are parallel. The term "parasagittal" is redundant: anything parallel with a sagittal plane is still sagittal.Any vertical plane that intersects the median plane at a right angle and separates the body into anterior and posterior parts is termed a coronal, or frontal, plane.The term horizontal plane refers to a plane at a right angle to both the median and coronal planes: it separates the body into superior and inferior parts. This is often termed an axial plane, particularly in radiology.The term transverse means at a right angle to the longitudinal axis of a structure. Thus, a transverse section through an artery is not necessarily horizontal. A transverse section through the hand is horizontal, whereas a transverse section through the foot is coronal The term medial means nearer to the median plane, and lateral means farther from it. Thus, in the anatomical position, the thumb is lateral to the little finger, whereas the big toe is medial to the little toe. Intermediate means lying between two structures, one of which is medial and the other lateral. In the upper limb radial means lateral and ulnar means medial: in the lower limb fibular or peroneal means lateral and tibial means medial. The border of a limb on which either the thumb or the big toe is situated is sometimes called preaxial, and the opposite border, postaxial. These two terms are based on the arrangement of the limbs in the embryo during the sixth postovulatory week, when the thumbs and the big toes are both on the rostral border of the limbs (see figs.?8-10?and?15-11).Medial and lateral rotation (which should never be referred to as internal and external) means rotation (e.g., of the hip) around a vertical axis so that the anterior aspect of the part moves medially or laterally, respectively.Anterior or ventral means nearer the front of the body. Posterior or dorsal means nearer the back. In the upper limb the term palmar (formerly volar) means anterior. In the foot, plantar means inferior, and the term dorsal is commonly used for superior in the foot.Superior means nearer the top or upper end of the body. Inferior means nearer the lower end. Cranial or cephalic is sometimes used in stead of superior, and caudal instead of inferior. Rostral means nearer the "front end," that is, the region of the nose and mouth. this is superior in the most of the body althoug it represents the anterior aspect of the head.The suffix "-ad" is sometimes added to a positional term to indicate the idea of motion. Thus, cephalad means proceeding toward the head. Such terms are useful occasionally in describing growth processes, but their application is best limited.In the limbs, proximal and distal are used to indicate, respectively, nearer to and farther from the root or attached end of the limb. (Proximal and distal have a special meaning in the case of the teeth.)Internal and external mean, respectively, nearer to and farther from the center of an organ or a cavity. Superficial and deep mean, respectively, nearer to and farther from the surface of the body.The term middle is used for a structure lying between two others that are anterior and posterior, or superior and inferior, or internal and external.In addition to the technical terms of position and direction, certain common expressions may be cautiously used in anatomical descriptions: front, back, in front of, behind, forward, backward, upper, lower, above, below, upward, downward, ascending, descending. These terms are free of ambiguity only if they are used in reference to the anatomical position. A number of other common terms, such as "under," however, are generally best avoided. In this work we will use technical terms of position and direction.History of anatomyAnatomy can be traced from the Greek period, B.C., and the Roman Empire, A.D., to Andreas Vesalius, who reformed the subject in his De humani corporis fabrica ("On the Workings of the Human Body") in 1543. Subsequent highlights include the discovery of the compound microscope (1590), the founding of microscopic anatomy by Malpighi (seventeenth century), the discovery of the circulation of the blood by Harvey (1628), the establishment of modern embryology by Wolff (eighteenth century), the gross classification of tissues by Bichat (1801), and many notable advances during the nineteenth and twentieth centuries.The best general introduction to the history of anatomy is Singer, C., A Short History of Anatomy and Physiology from the Greeks to Harvey, Dover, New York, 1957. Two other interesting works are Saunders, J. B. de C. M., and O'Malley, C. D., The Illustrations from the Works of Andreas Vesalius of Brussels, World Publishing Co., Cleveland, 1950; and O'Malley, C. D., and Saunders, J. B. de C. M., Leonardo da Vinci on the Human Body, Schuman, New York, anization of body cells tissues, organ systemsThe?cells?in complex multicellular organisms like people are?organized?into?tissues, groups of similarcells?that work together on a specific task. ... At each level of?organization—cells,?tissues,?organs, andorgan systems—structure is closely related to functionLevels of Organization. Some living things contain one cell that performs all needed functions. Multicellular organisms are made of many parts that are needed for survival. These parts are divided into?levels of organization. There are fivelevels: cells, tissue, organs, organ systems, and organisms.In biology,?tissue?is a cellular organizational level between?cells?and a complete organ. A?tissue?is an ensemble of similar?cells?and their extracellular matrix from the same origin that together carry out a specific function. Organs are then formed by the functional grouping together of multiple?anized?into tissues, and tissues form organs. Organs are?organized?into organ systems such as the skeletal and muscular systems.Life processes of the?human body?are maintained at several?levels?of structuralorganization. These include the chemical, cellular, tissue, organ, organ system, and the organism?level.Level 1 of Biological organization: The Biosphere. ...Level 2 of Biological Organization: Ecosystem. ...Level 3 of Biological Organization: Communities. ...Level 4 of Biological Organization: Population. ...Level 5 of Biological Organization: Organisms. ...Level 6: Organs and organ systems. ..Viral induction of?apoptosis?occurs when one or several cells of a living organism are infected with a virus, leading to cell death. Cell death in organisms is necessary for the normal development of cells and the cell cycle maturation. It is also important in maintaining the regular functions and activities of cells.The 11 organ systems of the body are the?integumentary, muscular,?skeletal,nervous,?circulatory, lymphatic,?respiratory,?endocrine, urinary/excretory,reproductive?and?digestive. Although each of your 11 organ systems has a unique function, each organ system also depends, directly or indirectly, on all the others.Function of cells which animal and plant cells have in commonPartFunctionCytoplasmMost chemical processes take place here, controlled by enzymesCell membraneControls the movement of substances into and out of the cellMitochondriaMost energy is released by respiration hereRibosomesProtein synthesis happens hereBiological membranes have three primary functions: (1) they keep toxic substances out of the cell; (2) they contain receptors and channels that allow specific molecules, such as ions, nutrients, wastes, and metabolic products, that mediate cellular and extracellular?activities?to pass between organelles and between the ...cardiovascular system?The?circulatory system, also called the?cardiovascular system?or thevascular system, is an organ?system?that permits blood to circulate and transport nutrients (such as amino acids and electrolytes), oxygen, carbon dioxide, hormones, and blood cells to and from the cells in the body to provide nourishment and help The heart?and circulatory system make up your cardiovascular system. Your heart works as a pump that pushes?blood?to the organs, tissues, and cells of your body. Blood delivers oxygen and nutrients to every cell and removes the carbon dioxide and waste products made by those cells. Blood is carried from your heart to the rest of your body through a complex network of arteries, arterioles, and capillaries. Blood is returned to your heart through venules and veins. If all the vessels of this network were laid end to end, they would extend for about 60,000 miles (more than 96,500 kilometers), which is far enough to circle?the?planet?Earth more than twice!The one-way system carries blood to all parts of your body. This process of blood flow within your body is called circulation.?Arteries?carry oxygen-rich blood away from your heart, and?veins?carry oxygen-poor blood back to your heart.In pulmonary circulation, though, the roles are switched. It is the pulmonary artery that brings oxygen-poor blood into your lungs and the pulmonary vein that brings oxygen-rich blood back to your heart.In the diagram, the vessels that carry oxygen-rich blood are colored red, and the vessels that carry oxygen-poor blood are colored blue. Click on the illustration for detailed views of the heart and cardiovascular system.Twenty major arteries make a path through your tissues, where they branch into smaller vessels called arterioles. Arterioles further branch into capillaries, the true deliverers of oxygen and nutrients to your cells. Most capillaries are thinner than a hair. In fact, many are so tiny only one blood cell can move through them at a time. Once the capillaries deliver oxygen and nutrients and pick up carbon dioxide and other waste, they move the blood back through wider vessels called venules. Venules eventually join to form veins, which deliver the blood back to your heart to pick up ic Respiratory system Date : 02/04/2018Anatomy and physiology and structureExpiration InspirationExchanges of gases Co2, O2 Related to disease also like Asthma, PneumoniaHuman Respiratory SystemThe?respiratory system?consists of all the organs involved in breathing. These include the nose,?pharynx,?larynx,?trachea,?bronchi?and?lungs. The respiratory system does two very important things: it brings oxygen into our bodies, which we need for our cells to live and function properly; and it helps us get rid of carbon dioxide, which is a waste product of cellular function. The nose, pharynx, larynx, trachea and bronchi all work like a system of pipes through which the air is funnelled down into our lungs. There, in very small air sacs called alveoli, oxygen is brought into the bloodstream and carbon dioxide is pushed from the blood out into the air. When something goes wrong with part of the respiratory system, such as an infection like?pneumonia, it makes it harder for us to get the oxygen we need and to get rid of the waste product carbon dioxide. Common respiratory symptoms include?breathlessness,?cough, and?chest rmation on re-publishing of our imagesThe Upper Airway and TracheaWhen you breathe in, air enters your body through your nose or mouth. From there, it travels down your throat through the larynx (or voicebox) and into the trachea (or windpipe) before entering your lungs. All these structures act to funnel fresh air down from the outside world into your body. The?upper airway?is important because it must always stay open for you to be able to breathe. It also helps to moisten and warm the air before it reaches your lungs.The LungsStructureThe lungs are paired, cone-shaped organs which take up most of the space in our chests, along with the heart. Their role is to take oxygen into the body, which we need for our cells to live and function properly, and to help us get rid of carbon dioxide, which is a waste product. We each have two lungs, a left lung and a right lung. These are divided up into ‘lobes’, or big sections of tissue separated by ‘fissures’ or dividers. The right lung has three lobes but the left lung has only two, because the heart takes up some of the space in the left side of our chest. The lungs can also be divided up into even smaller portions, called ‘bronchopulmonary segments’.These are pyramidal-shaped areas which are also separated from each other by membranes. There are about 10 of them in each lung. Each segment receives its own blood supply and air supply.How they workAir enters your lungs through a system of pipes called the bronchi. These pipes start from the bottom of the trachea as the left and right bronchi and branch many times throughout the lungs, until they eventually form little thin-walled air sacs or bubbles, known as the?alveoli. The alveoli are where the important work of gas exchange takes place between the air and your blood. Covering each alveolus is a whole network of little?blood vessel?called?capillaries, which are very small branches of the?pulmonary arteries. It is important that the air in the alveoli and the blood in the capillaries are very close together, so that oxygen and carbon dioxide can move (or diffuse) between them. So, when you breathe in, air comes down the trachea and through the bronchi into the alveoli. This fresh air has lots of oxygen in it, and some of this oxygen will travel across the walls of the alveoli into your bloodstream. Travelling in the opposite direction is carbon dioxide, which crosses from the blood in the capillaries into the air in the alveoli and is then breathed out. In this way, you bring in to your body the oxygen that you need to live, and get rid of the waste product carbon rmation on re-publishing of our images?Blood SupplyThe lungs are very vascular organs, meaning they receive a very large blood supply. This is because the pulmonary arteries, which supply the lungs, come directly from the right side of your heart. They carry blood which is low in oxygen and high in carbon dioxide into your lungs so that the carbon dioxide can be blown off, and more oxygen can be absorbed into the bloodstream. The newly oxygen-rich blood then travels back through the paired pulmonary veins into the left side of your heart. From there, it is pumped all around your body to supply oxygen to cells and organs.The Work of BreathingThe PleuraeThe lungs are covered by smooth membranes that we call?pleurae. The pleurae have two layers, a ‘visceral’ layer which sticks closely to the outside surface of your lungs, and a ‘parietal’ layer which lines the inside of your chest wall (ribcage). The pleurae are important because they help you breathe in and out smoothly, without any friction. They also make sure that when your ribcage expands on breathing in, your lungs expand as well to fill the extra space.The Diaphragm and Intercostal MusclesWhen you breathe in (inspiration), your muscles need to work to fill your lungs with air. The?diaphragm, a large, sheet-like muscle which stretches across your chest under the ribcage, does much of this work. At rest, it is shaped like a dome curving up into your chest. When you breathe in, the diaphragm contracts and flattens out, expanding the space in your chest and drawing air into your lungs. Other muscles, including the muscles between your ribs (the? HYPERLINK "" intercostal muscles) also help by moving your ribcage in and out. Breathing out (expiration) does not normally require your muscles to work. This is because your lungs are very elastic, and when your muscles relax at the end of inspiration your lungs simply recoil back into their resting position, pushing the air out as they go.The Respiratory System Through the AgesBreathing for the Premature BabyWhen a baby is born, it must convert from getting all of its oxygen through the placenta to absorbing oxygen through its lungs. This is a complicated process, involving many changes in both air and blood pressures in the baby’s lungs. For a baby born preterm (before 37 weeks gestation), the change is even harder. This is because the baby’s lungs may not yet be mature enough to cope with the transition. The major problem with a preterm baby’s lungs is a lack of something called ‘surfactant’. This is a substance produced by cells in the lungs which helps keep the air sacs, or alveoli, open. Without surfactant, the pressures in the lungs change and the smaller alveoli collapse.This reduces the area across which oxygen and carbon dioxide can be exchanged, and not enough oxygen will be taken in. Normally, a foetus will begin producing surfactant from around 28-32 weeks gestation. When a baby is born before or around this age, it may not have enough surfactant to keep its lungs open. The baby may develop something called ‘Neonatal Respiratory Distress Syndrome’, or NRDS. Signs of NRDS include tachypnoea (very fast breathing), grunting, and cyanosis (blueness of the lips and tongue). Sometimes NRDS can be treated by giving the baby artifically made surfactant by a tube down into the baby’s lungs.The Respiratory System and AgeingThe normal process of ageing is associated with a number of changes in both the structure and function of the respiratory system. These include:Enlargement of the alveoli. The air spaces get bigger and lose their elasticity, meaning that there is less area for gases to be exchanged across. This change is sometimes referred to as ‘senile emphysema’.The compliance (or springiness) of the chest wall decreases, so that it takes more effort to breathe in and out.The strength of the respiratory muscles (the diaphragm and intercostal muscles) decreases. This change is closely connected to the general health of the person.All of these changes mean that an older person might have more difficulty coping with increased stress on their respiratory system, such as with an infection like?pneumonia, than a younger person would.Musculo Sckeletal systemThe skeletal system includes the bones of the skeleton and the cartilages, ligaments, and other connective tissue that stabilize or connect the bones. In addition to supporting the weight of the body, bones work together with muscles to maintain the body’s position and to produce controlled, precise movements. Without the skeleton to pull against, contracting (tightened) muscle fibers could not make us sit, stand, walk, or run.BonesThere are 206 bones in the adult body. The bones perform five main functions for the body:Provide support: The skeletal system provides structural support for the entire body. Individual bones or groups of bones provide a framework for the attachment of soft tissues and organs.Store minerals and lipids: Calcium is the most abundant mineral in the body. (Ninety-nine percent of the body's calcium is found in the skeleton.) The calcium salts of bone are a valuable mineral reserve that maintains normal concentrations of calcium and phosphate ions in body fluids. The bones of the skeleton also store energy reserves as lipids (fats) in areas filled with yellow marrow.Produce blood cells: Red blood cells, white blood cells, and other blood elements are produced in the red marrow, which fills the internal cavities of many bones.Protect body organs: Many soft tissues and organs are surrounded by skeletal elements. For example, the rib cage protects the heart and lungs, the skull protects the brain, the vertebrae protect the spinal cord, and the pelvis protects the delicate reproductive organs.Provide leverage and movement: Many bones function as levers that can change the magnitude (strength) and direction of the forces generated by muscles.Bone structureEach bone in the skeleton contains two forms of tissue: compact (dense) bone that is relatively solid, and spongy (cancellous) bone that forms an open network of struts and plates. Compact bone is found on the external surface of the bone; spongy bone is located inside the bone.The amount of compact and spongy bone depends on the shape of the bone. Compact bone is thickest where stresses arrive from a limited range of directions. Spongy bone is located where bones are not heavily stressed or where stresses arrive from many directions. Spongy bone is much lighter than compact bone, which helps reduce the weight of the skeleton and makes it easier for muscles to move the bones.Bone development and growthThe growth of the skeleton determines the size and proportions of the body. Bones begin to form in a fetus about six weeks after fertilization, and portions of the skeleton do not stop growing until a person is about 25 years old.Most bones begin as hyaline cartilage. The cartilage is gradually converted to bone through a process called ossification. Bone growth begins at the center of the cartilage. As bones enlarge, bone growth activity shifts to the ends of the bones (an area commonly called the growth plate), which causes the bones to grow longer.Bone growth "factoids"Twenty percent of the adult skeleton is replaced each year.Moderate amounts of physical activity and weight-bearing activities are essential to stimulate bone maintenance and to maintain adequate bone strength.Other elements of the musculoskeletal systemJoints: These are where two bones interconnect. Each joint reflects a compromise between stability and range of motion. For example, the bones of the skull are very stable but with little motion, whereas the shoulder joint allows for a full range of motion but is a relatively unstable joint.Tendons: These attach muscle to bone.Ligaments: These attach bone to bone.Skeletal muscles: These muscles contract to pull on tendons and move the bones of the skeleton. Skeletal muscles also:Maintain posture and body position;Support soft tissues;Guard entrances and exits to the digestive and urinary tracts; and, Maintain body temperature.Nerves: Nerves control the contraction of skeletal muscles, interpret sensory information, and coordinate the activities of the body's organ systems.Cartilage: This is a type of connective tissue. It is a firm gel-like substance. The body contains three major types of cartilage:?hyaline?cartilage,?elastic?cartilage, and?fibrocartilage.Hyaline cartilage is the most common type of cartilage. It provides stiff but somewhat flexible support. Examples in adults include the tips of ribs (where they meet the sternum [breastbone]) and part of the nasal septum. Another example is articular cartilage, which covers the ends of bones within a joint. The surfaces of articular cartilage are slick and smooth, which reduces friction during joint movement.Elastic cartilage provides support but can tolerate distortion without damage and return to its original shape. Elastic cartilage can be found in the external flap of the ear, among other places.Fibrocartilage resists compression, prevents bone-to-bone contact, and limits relative movement. Fibrocartilage can be found within the knee joint, between the pubic bones of the pelvis, and between the spinal vertebrae.Cartilage heals poorly, and damaged fibrocartilage in joints such as the knee can interfere with normal movements. The knee contains both hyaline cartilage and fibrocartilage. The hyaline cartilage covers bony surfaces; fibrocartilage pads in the joint prevent contact between bones during movement. Injuries to the joints can produce tears in the fibrocartilage pads, and the tears do not heal. Eventually, joint mobility is severely reduced.The Digestive SystemDigestion is the process by which the body breaks down food into absorbable nutrients. The body absorbs and assimilates everything that we ingest. Digestion includes physical actions such as chewing and peristalsis (involuntary contraction and dilation of muscles to force forward movement), as well as the chemical actions of enzymes, bile and acids.The MouthAs soon as we place food in our mouth the digestive system starts to work by biting and chewing. Only one digestive enzyme, amylase (for starch), is present in the mouth. However, food is normally not in the mouth long enough to permit complete digestion and little nutrient absorption takes place in the mouth.The StomachThe primary function of the stomach is to break large proteins into smaller peptides and peptones. Pepsin is an enzyme produced in the acidic environment of?the stomach (1.5 to 7.0 pH) which digests proteins into smaller peptides of varying lengths. Other enzymes such as gelatinase (for gelatin) digest specific proteins.Amylase (the enzyme that breaks down starch) is inactivated, or destroyed, when stomach pH falls below 6.5. Before this happens however, up to 50% of starches may be partially broken down. Some fat is emulsified (broken up into smaller pieces) in the stomach by bile acids, and the enzyme lipase, to aid digestion in the small intestine. At the average stomach pH of 2.0, however, most fat is formed into large globules that pass unchanged into the small intestine. Small amounts of sucrose (table sugar) may be broken apart into glucose and fructose by acid hydrolysis from the bile acids in the stomach.The IntestinesVirtually all absorption of nutrients (macronutrients such as carbohydrates and fats and micronutrients such as vitamins and minerals) occurs in the intestines. Absorption of nutrients is, in fact, the primary function of the small intestine. Most carbohydrates, for instance, are absorbed in the small intestine. The pancreatic enzymes secreted into the small intestine also contain amylase which breaks down starches into a disaccharide (two sugars joined together) called maltose. In the intestines, enzymes such as maltase and lactase break disaccharides into single sugars (monosaccharides), such as glucose. When adults and older children do not have enough lactase to digest lactose (the sugar in milk) lactose intolerance results and milk cannot be completely digested.When food leaves the stomach, digestion is completed in the small intestine with the help of the enzymes secreted by the pancreas (lipase, amylase, protease, maltase, trypsin and chymotrypsin). The pH of food mass increases from about 2.0 to 6.5 (still slightly acidic), as it passes from the stomach through the small intestine to the colon. Very few nutrients, except water, is absorbed by the large intestine (colon)EnzymesAn enzyme is a protein that acts as a catalyst in a biological reaction. It binds itself to a substance and converts it into another substance. Enzymes are very specific in their functions, which is why there are different enzymes for different biological reactions. In the case of digestion, distinct forms of food require specific enzymes. Unless proteins, fats and carbohydrates (sugars) are reduced to smaller absorbable components they will remain in the digestive track. The following list gives a glance for what each enzyme breaks and where it is produced:Amylase?- starches into maltose (a disaccharide): saliva and pancreas - released into the small intestineLipase?- fats (lipids): in stomach and pancreas - released into the small intestinePepsin?- proteins into absorbable peptides and peptones: stomachGelatinase?- gelatin: stomachMaltase?- maltose? into monosaccharides: produced by the pancreas - released into the small intestineLactase?- lactose into monosaccharides: small intestineTrypson?- proteins into peptides and amino acids: pancreas - released into small intestineChymotrypson?- proteins into peptides and amino acids: pancreases - released into small intestineThe following chart explains where action and what action takes place in a fully functional digestive system:OrgansEnzymesActionmouthAmylase in salivamechanical digestion of all food (teeth chewing & grinding) chemical digestion of carbohydrates begins with amylaseoesophagusnonefood passes from mouth through the oesophagus to the stomachstomachpepsingastric juicehydrochloric acidlipase, gelatinasemechanical digestion of food (churning of stomach walls) and chemical digestion of proteins begins with pepsin while lipase breaks some of the fats and gelatinase breaks down gelatinssmall intestinepancreatic juiceintestinal juicebile, lipase, maltase, lactase?chemical digestion of carbohydrates, proteins, & lipids continues & is completedthe small, soluble nutrients (sugars, amino acids, fatty acids) are absorbedlarge intestinenonewater is absorbed from unusable, indigestible wastes (faeces) MouthThe?mouth?is the first part of the?gastrointestinal tract?and is equipped with several structures that begin the first processes of digestion.[3]?These include salivary glands, teeth and the tongue. The mouth consists of two regions; the vestibule and the oral cavity proper. The vestibule is the area between the teeth, lips and cheeks, HYPERLINK "" \l "cite_note-4" [4]?and the rest is the oral cavity proper. Most of the oral cavity is lined with?oral mucosa, a?mucous membrane?that produces a lubricating?mucus, of which only a small amount is needed. Mucous membranes vary in structure in the different regions of the body but they all produce a lubricating mucus, which is either secreted by surface cells or more usually by underlying glands. The mucous membrane in the mouth continues as the thin mucosa which lines the bases of the teeth. The main component of mucus is a?glycoprotein?called? HYPERLINK "" \o "Mucin" mucin?and the type secreted varies according to the region involved. Mucin is viscous, clear, and clinging. Underlying the mucous membrane in the mouth is a thin layer of?smooth muscle tissue?and the loose connection to the membrane gives it its great elasticity.[5]?It covers the cheeks, inner surfaces of the?lips, and floor of the mouth.[6]:1186The roof of the mouth is termed the?palate?and it separates the oral cavity from the nasal cavity. The palate is hard at the front of the mouth since the overlying mucosa is covering a plate of?bone; it is softer and more pliable at the back being made of muscle and connective tissue, and it can move to swallow food and liquids. The?soft palate?ends at the?uvula.[7]?The surface of the?hard palate?allows for the pressure needed in eating food, to leave the nasal passage clear.[8]?The lips are the mouth's front boundary and the? HYPERLINK "(anatomy)" \o "Fauces (anatomy)" fauces?(the passageway between the tonsils, also called the throat), HYPERLINK "" \l "cite_note-Dorland's-6" [6]:686?mark its posterior boundary.At either side of the soft palate are the? HYPERLINK "" \o "Palatoglossus muscle" palatoglossus muscles?which also reach into regions of the tongue. These muscles raise the back of the tongue and also close both sides of the fauces to enable food to be swallowed.[6]:1208?Mucus helps in the mastication of food in its ability to soften and collect the food in the formation of the bolus.Salivary glandsOral cavityThere are three pairs of main?salivary glands?and between 800 and 1,000 minor salivary glands, all of which mainly serve the digestive process, and also play an important role in the maintenance of dental health and general mouth lubrication, without which speech would be impossible.[9]?The main glands are all?exocrine glands, secreting via ducts. All of these glands terminate in the mouth. The largest of these are the?parotid glands—their secretion is mainly?serous. The next pair are underneath the jaw, the? HYPERLINK "" \o "Submandibular gland" submandibular glands, these produce both?serous fluid?and?mucus. The serous fluid is produced by?serous glands?in these salivary glands which also produce?lingual lipase. They produce about 70% of the oral cavity saliva. The third pair are the?sublingual glands?located underneath the tongue and their secretion is mainly mucous with a small percentage of saliva.Within the?oral mucosa?(a?mucous membrane) lining the mouth and also on the tongue and palates and mouth floor, are the minor salivary glands; their secretions are mainly mucous and are innervated by the?facial nerve?(the seventh?cranial nerve).[10]?The glands also secrete?amylase?a first stage in the breakdown of food acting on the carbohydrate in the food to transform the starch content into maltose. There are other glands on the surface of the tongue that encircle?taste buds?on the back part of the tongue and these also produce lingual lipase.?Lipase?is a?digestive enzyme?that catalyses the?hydrolysis?of?lipids?(fats). These glands are termed?Von Ebner's glands?which have also been shown to have another function in the secretion of? HYPERLINK "" \o "Histatin" histatins?which offer an early defense (outside of the immune system) against microbes in food, when it makes contact with these glands on the tongue tissue.[9][11]?Sensory information can stimulate the secretion of saliva providing the necessary fluid for the tongue to work with and also to ease swallowing of the food.SalivaMain article:?SalivaSaliva?moistens and softens food, and along with the chewing action of the teeth, transforms the food into a smooth?bolus. The bolus is further helped by the lubrication provided by the saliva in its passage from the mouth into the esophagus. Also of importance is the presence in saliva of the digestive enzymes?amylase?and?lipase. Amylase starts to work on the?starch?in?carbohydrates, breaking it down into the simple?sugars?of?maltose?and?dextrose?that can be further broken down in the small intestine. Saliva in the mouth can account for 30% of this initial starch digestion. Lipase starts to work on breaking down?fats. Lipase is further produced in the? HYPERLINK "" \o "Pancreas" pancreaswhere it is released to continue this digestion of fats. The presence of salivary lipase is of prime importance in young babies whose pancreatic lipase has yet to be developed.[12]As well as its role in supplying?digestive enzymes, saliva has a cleansing action for the teeth and mouth.[13]?It also has an?immunological?role in supplying antibodies to the system, such as?immunoglobulin A.[14]?This is seen to be key in preventing?infections?of the salivary glands, importantly that of? HYPERLINK "" \o "Parotitis" parotitis.Saliva also contains a?glycoprotein?called? HYPERLINK "" \o "Haptocorrin" haptocorrin?which is a binding protein to vitamin B12.[15]?It binds with the vitamin in order to carry it safely through the acidic content of the stomach. When it reaches the duodenum, pancreatic enzymes break down the glycoprotein and free the vitamin which then binds with?intrinsic factor.TongueFood enters the mouth where the first stage in the digestive process takes place, with the action of the?tongue?and the secretion of saliva. The tongue is a fleshy and?muscular?sensory organ, and the very first sensory information is received via the taste buds in the?papillae?on its surface. If the taste is agreeable, the tongue will go into action, manipulating the food in the mouth which stimulates the secretion of saliva from the salivary glands. The liquid quality of the saliva will help in the softening of the food and its enzyme content will start to break down the food whilst it is still in the mouth. The first part of the food to be broken down is the starch of carbohydrates (by the?enzyme?amylase?in the saliva).The tongue is attached to the floor of the mouth by a ligamentous band called the? HYPERLINK "" \o "Frenum" frenum[5]?and this gives it great mobility for the manipulation of food (and?speech); the range of manipulation is optimally controlled by the action of several muscles and limited in its external range by the stretch of the frenum. The tongue's two sets of muscles, are four?intrinsic musclesthat originate in the tongue and are involved with its shaping, and four?extrinsic muscles?originating in?bone?that are involved with its movement.TasteMain article:?TasteCross section of? HYPERLINK "" \o "Circumvallate papilla" circumvallate papilla?showing arrangement of nerves and taste budsTaste?is a form of?chemoreception?that takes place in the specialised?taste receptors, contained in structures called?taste budsin the mouth. Taste buds are mainly on the upper surface (dorsum) of the tongue. The function of taste perception is vital to help prevent harmful or rotten foods from being consumed. There are also taste buds on the?epiglottis?and upper part of the?esophagus. The taste buds are innervated by a branch of the facial nerve the? HYPERLINK "" \o "Chorda tympani" chorda tympani, and the? HYPERLINK "" \o "Glossopharyngeal nerve" glossopharyngeal nerve. Taste messages are sent via these?cranial nerves?to the?brain. The brain can distinguish between the chemical qualities of the food. The five?basic tastes?are referred to as those of?saltiness,?sourness,?bitterness,?sweetness, and? HYPERLINK "" \o "Umami" umami. The detection of saltiness and sourness enables the control of salt and acid balance. The detection of bitterness warns of poisons—many of a plant's defences are of poisonous compounds that are bitter. Sweetness guides to those foods that will supply energy; the initial breakdown of the energy-giving carbohydrates by salivary amylase creates the taste of sweetness since simple sugars are the first result. The taste of umami is thought to signal protein-rich food. Sour tastes are acidic which is often found in bad food. The brain has to decide very quickly whether the food should be eaten or not. It was the findings in 1991, describing the first?olfactory?receptors that helped to prompt the research into taste. The olfactory receptors are located on cell surfaces in the?nose?which bind to chemicals enabling the detection of smells. It is assumed that signals from taste receptors work together with those from the nose, to form an idea of complex food flavours.[16]TeethMain article:?Human toothTeeth?are complex structures made of materials specific to them. They are made of a bone-like material called?dentin, which is covered by the hardest tissue in the body—enamel.[8]?Teeth have different shapes to deal with different aspects of?mastication?employed in tearing and chewing pieces of food into smaller and smaller pieces. This results in a much larger surface area for the action of digestive enzymes. The teeth are named after their particular roles in the process of mastication—incisors?are used for cutting or biting off pieces of food;?canines, are used for tearing,?premolars?and?molars?are used for chewing and grinding. Mastication of the food with the help of saliva and mucus results in the formation of a soft bolus which can then be?swallowed?to make its way down the?upper gastrointestinal tract?to the stomach.[citation needed]?The digestive enzymes in saliva also help in keeping the teeth clean by breaking down any lodged food particles.[citation needed]EpiglottisMain article:?EpiglottisThe?epiglottis?is a flap of?elastic cartilage?attached to the entrance of the?larynx. It is covered with a mucous membrane and there are taste buds on its lingual surface which faces into the mouth.[17]?Its laryngeal surface faces into the larynx. The epiglottis functions to guard the entrance of the?glottis, the opening between the?vocal folds. It is normally pointed upward during breathing with its underside functioning as part of the pharynx, but during swallowing, the epiglottis folds down to a more horizontal position, with its upper side functioning as part of the pharynx. In this manner it prevents food from going into the trachea and instead directs it to the esophagus, which is behind. During swallowing, the backward motion of the tongue forces the epiglottis over the glottis' opening to prevent any food that is being swallowed from entering the larynx which leads to the lungs; the larynx is also pulled upwards to assist this process. Stimulation of the larynx by ingested matter produces a strong?cough reflex?in order to protect the lungs.PharynxMain article:?PharynxThe?pharynx?is a part of the?conducting zone?of the?respiratory system?and also a part of the digestive system. It is the part of the throat immediately behind the?nasal cavity?at the back of the mouth and above the esophagus and?larynx. The pharynx is made up of three parts. The lower two parts—the? HYPERLINK "" \o "Oropharynx" oropharynx?and the? HYPERLINK "" \o "Laryngopharynx" laryngopharynx?are involved in the digestive system. The laryngopharynx connects to the esophagus and it serves as a passageway for both air and food. Air enters the larynx anteriorly but anything swallowed has priority and the passage of air is temporarily blocked. The pharynx is innervated by the?pharyngeal plexus of the vagus nerve.[18]?Muscles in the pharynx push the food into the esophagus. The pharynx joins the esophagus at the oesophageal inlet which is located behind the? HYPERLINK "" \o "Cricoid cartilage" cricoid cartilage.EsophagusMain article:?EsophagusThe?esophagus, commonly known as the gullet, is an organ which consists of a muscular tube through which food passes from the pharynx to the stomach. The esophagus is continuous with the laryngeal part of the pharynx. It passes through the posterior? HYPERLINK "" \o "Mediastinum" mediastinum?in the?thorax?and enters the?stomach?through a hole in the?thoracic diaphragm—the?esophageal hiatus, at the level of the tenth?thoracic vertebra?(T10). Its length averages 25?cm, varying with height. It is divided into cervical,?thoracic?and?abdominal?parts. The pharynx joins the esophagus at the esophageal inlet which is behind the? HYPERLINK "" \o "Cricoid cartilage" cricoid cartilage.At rest the esophagus is closed at both ends, by the upper and lower esophageal?sphincters. The opening of the upper sphincter is triggered by the?swallowing reflexso that food is allowed through. The sphincter also serves to prevent back flow from the esophagus into the pharynx. The esophagus has a mucous membrane and the epithelium which has a protective function is continuously replaced due to the volume of food that passes inside the esophagus. During swallowing, food passes from the mouth through the pharynx into the esophagus. The epiglottis folds down to a more horizontal position so as to prevent food from going into the?trachea, instead directing it to the esophagus.Once in the esophagus, the bolus travels down to the stomach via rhythmic contraction and relaxation of muscles known as?peristalsis. The lower esophageal sphincter is a muscular sphincter surrounding the lower part of the esophagus. The junction between the esophagus and the stomach (the gastroesophageal junction) is controlled by the lower esophageal sphincter, which remains constricted at all times other than during swallowing and vomiting to prevent the contents of the stomach from entering the esophagus. As the esophagus does not have the same protection from acid as the stomach, any failure of this sphincter can lead to heartburn. The esophagus has a mucous membrane of epithelium which has a protective function as well as providing a smooth surface for the passage of food. Due to the high volume of food that is passed over time, this membrane is continuously renewed.DiaphragmThe?diaphragm?is an important part of the body's digestive system. The muscular diaphragm separates the?thoracic cavity?from the?abdominal cavity?where most of the digestive organs are located. The? HYPERLINK "" \o "Suspensory muscle of the duodenum" suspensory muscle?attaches the ascending duodenum to the diaphragm. This muscle is thought to be of help in the digestive system in that its attachment offers a wider angle to the? HYPERLINK "" \o "Duodenojejunal flexure" duodenojejunal flexure?for the easier passage of digesting material. The diaphragm also attaches to, and anchors the liver at its?bare area. The esophagus enters the abdomen through a?hole in the diaphragm?at the level of?T10.StomachMain article:?StomachAreas of the stomachThe?stomach?is a major organ of the gastrointestinal tract and digestive system. It is a consistently J-shaped organ joined to the esophagus at its upper end and to the duodenum at its lower end.?Gastric acid?(informally?gastric juice), produced in the stomach plays a vital role in the digestive process, and mainly contains?hydrochloric acid?and?sodium chloride. A?peptide hormone,? HYPERLINK "" \o "Gastrin" gastrin, produced by?G cells?in the?gastric glands, stimulates the production of gastric juice which activates the?digestive enzymes.? HYPERLINK "" \o "Pepsinogen" Pepsinogen?is a precursor enzyme ( HYPERLINK "" \o "Zymogen" zymogen) produced by the?gastric chief cells, and gastric acid activates this to the enzyme?pepsin?which begins the digestion of?proteins. As these two chemicals would damage the stomach wall, mucus is secreted by innumerable gastric glands in the stomach, to provide a slimy protective layer against the damaging effects of the chemicals on the inner layers of the stomach.At the same time that protein is being digested, mechanical churning occurs through the action of?peristalsis, waves of muscular contractions that move along the stomach wall. This allows the mass of food to further mix with the?digestive enzymes.?Gastric lipase?secreted by the chief cells in the? HYPERLINK "" \o "Gastric glands" fundic glands?in the?gastric mucosa?of the stomach, is an acidic lipase, in contrast with the alkaline pancreatic lipase. This breaks down fats to some degree though is not as efficient as the pancreatic lipase.The?pylorus, the lowest section of the stomach which attaches to the?duodenum?via the?pyloric canal, contains countless glands which secrete digestive enzymes including gastrin. After an hour or two, a thick semi-liquid called? HYPERLINK "" \o "Chyme" chyme?is produced. When the?pyloric sphincter, or valve opens, chyme enters the duodenum where it mixes further with digestive enzymes from the pancreas, and then passes through the small intestine, where digestion continues. When the chyme is fully digested, it is absorbed into the blood. 95% of absorption of nutrients occurs in the small intestine. Water and minerals are reabsorbed back into the blood in the colon of the large intestine, where the environment is slightly acidic. Some vitamins, such as?biotin?and?vitamin K?produced by?bacteria?in the?gut flora?of the colon are also absorbed.The?parietal cells?in the fundus of the stomach, produce a?glycoprotein?called?intrinsic factor?which is essential for the absorption of?vitamin B12. Vitamin B12 (cobalamin), is carried to, and through the stomach, bound to a glycoprotein secreted by the salivary glands -? HYPERLINK "" \o "Transcobalamin" transcobalamin I?also called? HYPERLINK "" \o "Haptocorrin" haptocorrin, which protects the acid-sensitive vitamin from the acidic stomach contents. Once in the more neutral duodenum, pancreatic enzymes break down the protective glycoprotein. The freed vitamin B12 then binds to intrinsic factor which is then absorbed by the? HYPERLINK "" \o "Enterocyte" enterocytes?in the ileum.The stomach is a distensible organ and can normally expand to hold about one litre of food.[19]?This expansion is enabled by a series of?gastric folds?in the inner walls of the stomach. The stomach of a newborn baby will only be able to expand to retain about 30 ml.SpleenMain article:?SpleenThe?spleen?breaks down both red and white?blood cells?that are?spent. This is why it is sometimes known as the 'graveyard of red blood cells'. A product of this?digestion?is the pigment? HYPERLINK "" \o "Bilirubin" bilirubin, which is sent to the?liver?and secreted in the?bile. Another product is?iron, which is used in the formation of new blood cells in the?bone marrow.[5]?Medicine?treats the spleen solely as belonging to the?lymphatic system, though it is acknowledged that the full range of its important functions is not yet understood.[20]LiverThe?liver?is the second largest organ (after the?skin) and is an accessory digestive gland which plays a role in the body's?metabolism. The liver has many functions some of which are important to digestion. The liver can detoxify various?metabolites; synthesise?proteins?and produce? HYPERLINK "" \o "Biochemical" biochemicals?needed for digestion. It regulates the storage of?glycogen?which it can form from?glucose( HYPERLINK "" \o "Glycogenesis" glycogenesis). The liver can also synthesise glucose from certain?amino acids. Its digestive functions are largely involved with the breaking down of?carbohydrates. It also maintains protein metabolism in its synthesis and degradation. In?lipid?metabolism it synthesises?cholesterol.?Fats?are also produced in the process of? HYPERLINK "" \o "Lipogenesis" lipogenesis. The liver synthesises the bulk of lipoproteins. The liver is located in the upper right quadrant of the abdomen and below the diaphragm to which it is attached at one part, This is to the right of the stomach and it overlies the?gall bladder. The liver produces?bile, an important alkaline compound which aids digestion.BileBile?produced by the liver is made up of water (97%),?bile salts, mucus and?pigments, 1% fats and inorganic salts.[21]? HYPERLINK "" \o "Bilirubin" Bilirubin?is its major pigment. Bile acts partly as a?surfactant?which lowers the surface tension between either two liquids or a solid and a liquid and helps to?emulsify?the fats in the? HYPERLINK "" \o "Chyme" chyme. Food fat is dispersed by the action of bile into smaller units called?micelles. The breaking down into micelles creates a much larger surface area for the pancreatic enzyme,?lipase?to work on. Lipase digests the?triglycerides?which are broken down into two?fatty acids?and a? HYPERLINK "" \o "Monoglyceride" monoglyceride. These are then absorbed by? HYPERLINK "" \o "Intestinal villi" villi?on the intestinal wall. If fats are not absorbed in this way in the small intestine problems can arise later in the large intestine which is not equipped to absorb fats. Bile also helps in the absorption of?vitamin K?from the diet. Bile is collected and delivered through the?common hepatic duct. This duct joins with the?cystic duct?to connect in a?common bile duct?with the gallbladder. Bile is stored in the gallbladder for release when food is discharged into the duodenum and also after a few hours.[22]GallbladderThe?gallbladder?is a hollow part of the? HYPERLINK "" \o "Biliary tract" biliary tract?that sits just beneath the liver, with the gallbladder body resting in a small depression.[23]?It is a small organ where the?bile?produced by the liver is stored, before being released into the small intestine. Bile flows from the liver through the?bile ducts?and into the gall bladder for storage. The bile is released in response to? HYPERLINK "" \o "Cholecystokinin" cholecystokinin?(CCK) a?peptide hormone?released from the duodenum. The production of CCK (by endocrine cells of the duodenum) is stimulated by the presence of fat in the duodenum.[24]It is divided into three sections, a fundus, body and neck. The neck tapers and connects to the biliary tract via the?cystic duct, which then joins the?common hepatic ductto form the?common bile duct. At this junction is a mucosal fold called?Hartmann's pouch, where?gallstones?commonly get stuck. The?muscular layer?of the body is of smooth muscle tissue that helps the gallbladder contract, so that it can discharge its bile into the bile duct. The gallbladder needs to store bile in a natural, semi-liquid form at all times.?Hydrogen ions?secreted from the inner lining of the gallbladder keep the bile acidic enough to prevent hardening. To dilute the bile, water and?electrolytes?from the digestion system are added. Also, salts attach themselves to cholesterol molecules in the bile to keep them from? HYPERLINK "" \o "Crystallization" crystallising. If there is too much cholesterol or bilirubin in the bile, or if the gallbladder doesn't empty properly the systems can fail. This is how gallstones form when a small piece of calcium gets coated with either cholesterol or bilirubin and the bile crystallises and forms a gallstone. The main purpose of the gallbladder is to store and release bile, or?gall. Bile is released into the small intestine in order to help in the digestion of fats by breaking down larger molecules into smaller ones. After the fat is absorbed, the bile is also absorbed and transported back to the liver for reuse.PancreasMain article:?PancreasAction of digestive hormonesPancreas, duodenum and bile ductThe?pancreas?is a major organ functioning as an accessory digestive gland in the digestive system. It is both an?endocrine gland?and an?exocrine gland.[25]?The endocrine part secretes?insulin?when the?blood sugar?becomes high; insulin moves glucose from the blood into the muscles and other tissues for use as energy. The endocrine part releases?glucagon?when the blood sugar is low; glucagon allows stored sugar to be broken down into?glucose?by the liver in order to re-balance the sugar levels. The pancreas produces and releases important digestive enzymes in the?pancreatic juice?that it delivers to the duodenum. The pancreas lies below and at the back of the stomach. It connects to the duodenum via the?pancreatic duct?which it joins near to the bile duct's connection where both the bile and pancreatic juice can act on the? HYPERLINK "" \o "Chyme" chyme?that is released from the stomach into the duodenum. Aqueous pancreatic secretions from?pancreatic duct cells?contain?bicarbonate?ions which are alkaline and help with the bile to neutralise the acidic chyme that is churned out by the stomach.The pancreas is also the main source of enzymes for the digestion of?fats?and proteins. Some of these are released in response to the production of?CKK?in the duodenum. (The enzymes that digest polysaccharides, by contrast, are primarily produced by the walls of the intestines.) The cells are filled with secretory granules containing the precursor digestive enzymes. The major?proteases, the pancreatic enzymes which work on proteins, are? HYPERLINK "" \o "Trypsinogen" trypsinogen?and? HYPERLINK "" \o "Chymotrypsinogen" chymotrypsinogen.? HYPERLINK "" \o "Elastase" Elastase?is also produced. Smaller amounts of lipase and amylase are secreted. The pancreas also secretes? HYPERLINK "" \o "Phospholipase A2" phospholipase A2,? HYPERLINK "" \o "Lysophospholipase" lysophospholipase, and?cholesterol?esterase. The precursor?zymogens, are inactive variants of the enzymes; which avoids the onset of?pancreatitis?caused by autodegradation. Once released in the intestine, the enzyme? HYPERLINK "" \o "Enteropeptidase" enteropeptidase?present in the intestinal mucosa activates trypsinogen by cleaving it to form trypsin; further cleavage results in chymotripsin.Lower gastrointestinal tractMain article:?Gastrointestinal tractThe lower gastrointestinal tract (GI), includes the?small intestine?and all of the?large intestine.[26]?The intestine is also called the bowel or the gut. The lower GI starts at the pyloric sphincter of the stomach and finishes at the anus. The small intestine is subdivided into the?duodenum, the?jejunum?and the?ileum. The cecum marks the division between the small and large intestine. The large intestine includes the rectum and?anal canal.[1]Small intestineLower GI tract - 3) Small intestine; 5) Cecum; 6) Large intestineDuodenumFood starts to arrive in the?small intestine?one hour after it is eaten, and after two hours the stomach has emptied. Until this time the food is termed a bolus. It then becomes the partially digested semi-liquid termed? HYPERLINK "" \o "Chyme" chyme.In the small intestine, the?pH?becomes crucial; it needs to be finely balanced in order to activate digestive enzymes. The chyme is very acidic, with a low pH, having been released from the stomach and needs to be made much more alkaline. This is achieved in the?duodenum?by the addition of bile from the gall bladder combined with the?bicarbonate?secretions from the pancreatic duct and also from secretions of bicarbonate-rich mucus from duodenal glands known as?Brunner's glands. The chyme arrives in the intestines having been released from the stomach through the opening of the?pyloric sphincter. The resulting alkaline fluid mix neutralises the gastric acid which would damage the lining of the intestine. The mucus component lubricates the walls of the intestine.When the digested food particles are reduced enough in size and composition, they can be absorbed by the intestinal wall and carried to the bloodstream. The first receptacle for this chyme is the?duodenal bulb. From here it passes into the first of the three sections of the small intestine, the duodenum. (The next section is the?jejunum?and the third is the?ileum). The duodenum is the first and shortest section of the small intestine. It is a hollow, jointed C-shaped tube connecting the stomach to the jejunum. It starts at the duodenal bulb and ends at the? HYPERLINK "" \o "Suspensory muscle of duodenum" suspensory muscle of duodenum. The attachment of the suspensory muscle to the diaphragm is thought to help the passage of food by making a wider angle at its attachment.Most food digestion takes place in the small intestine.?Segmentation contractions?act to mix and move the chyme more slowly in the small intestine allowing more time for absorption (and these continue in the large intestine). In the duodenum, pancreatic lipase is secreted together with a?co-enzyme,? HYPERLINK "" \o "Colipase" colipase?to further digest the fat content of the chyme. From this breakdown, smaller particles of emulsified fats called? HYPERLINK "" \o "Chylomicron" chylomicrons?are produced. There are also digestive cells called? HYPERLINK "" \o "Enterocyte" enterocytes?lining the intestines (the majority being in the small intestine). They are unusual cells in that they have? HYPERLINK "" \o "Intestinal villus" villi?on their surface which in turn have innumerable? HYPERLINK "" \o "Microvilli" microvilli?on their surface. All these villi make for a greater surface area, not only for the absorption of chyme but also for its further digestion by large numbers of digestive enzymes present on the microvilli.The chylomicrons are small enough to pass through the enterocyte villi and into their?lymph?capillaries called?lacteals. A milky fluid called? HYPERLINK "" \o "Chyle" chyle, consisting mainly of the emulsified fats of the chylomicrons, results from the absorbed mix with the lymph in the lacteals.[HYPERLINK "" \o "Wikipedia:Please clarify"clarification needed]?Chyle is then transported through the?lymphatic system?to the rest of the body.The suspensory muscle marks the end of the duodenum and the division between the upper gastrointestinal tract and the lower GI tract. The digestive tract continues as the jejunum which continues as the ileum. The jejunum, the midsection of the small intestine contains?circular folds, flaps of doubled mucosal membrane which partially encircle and sometimes completely encircle the?lumen?of the intestine. These folds together with villi serve to increase the surface area of the jejunum enabling an increased absorption of digested sugars, amino acids and fatty acids into the bloodstream. The circular folds also slow the passage of food giving more time for nutrients to be absorbed.The last part of the small intestine is the ileum. This also contains villi and?vitamin B12; bile acids and any residue nutrients are absorbed here. When the chyme is exhausted of its nutrients the remaining waste material changes into the semi-solids called feces, which pass to the large intestine, where bacteria in the?gut florafurther break down residual proteins and starches.[27]CecumCecum and beginning of ascending colonThe? HYPERLINK "" \o "Cecum" cecum?is a pouch marking the division between the small intestine and the large intestine.[28]?The cecum receives chyme from the last part of the small intestine, the?ileum, and connects to the?ascending colon?of the large intestine. At this junction there is a sphincter or valve, the? HYPERLINK "" \o "Ileocecal valve" ileocecal valve?which slows the passage of chyme from the ileum, allowing further digestion. It is also the site of the?appendix?attachment.Large intestineIn the?large intestine, HYPERLINK "" \l "cite_note-eb-1" [1]?the passage of the digesting food in the?colon?is a lot slower, taking from 12 to 50 hours until it is removed by?defecation. The colon mainly serves as a site for the fermentation of digestible matter by the?gut flora. The time taken varies considerably between individuals. The remaining semi-solid waste is termed?feces?and is removed by the coordinated contractions of the intestinal walls, termed?peristalsis, which propels the?excreta?forward to reach the? HYPERLINK "" \o "Rectum" rectumand exit via defecation from the anus. The wall has an outer layer of longitudinal muscles, the? HYPERLINK "" \o "Taeniae coli" taeniae coli, and an inner layer of circular muscles. The circular muscle keeps the material moving forward and also prevents any back flow of waste. Also of help in the action of peristalsis is the?basal electrical rhythm?that determines the frequency of contractions.[29]?The taeniae coli can be seen and are responsible for the bulges ( HYPERLINK "(anatomy)" \o "Haustrum (anatomy)" haustra) present in the colon. Most parts of the GI tract are covered with?serous membranes?and have a?mesentery. Other more muscular parts are lined with?adventitia.Blood supplyBlood supply to the digestive organs HYPERLINK "" \l "cite_note-Moore150-30" [30]Arteries and veins around the pancreas and spleenThe digestive system is supplied by the?celiac artery. The celiac artery is the first major branch from the?abdominal aorta, and is the only major artery that nourishes the digestive organs.There are three main divisions – the?left gastric artery, the?common hepatic artery?and the? HYPERLINK "" \o "Splenic artery" splenic artery.The celiac artery supplies the liver, stomach, spleen and the upper 1/3 of the duodenum (to the?sphincter of Oddi) and the pancreas with oxygenated blood. Most of the blood is returned to the liver via the?portal venous system?for further processing and detoxification before returning to the?systemic circulation?via the?hepatic portal vein.The next branch from the abdominal aorta is the?superior mesenteric artery, which supplies the regions of the digestive tract derived from the midgut, which includes the distal 2/3 of the duodenum, jejunum, ileum, cecum, appendix, ascending colon, and the proximal 2/3 of the transverse colon.The final branch which is important for the digestive system is the?inferior mesenteric artery, which supplies the regions of the digestive tract derived from the hindgut, which includes the distal 1/3 of the transverse colon, descending colon, sigmoid colon, rectum, and the anus above the? HYPERLINK "" \o "Pectinate line" pectinate line.Nerve supplyThe?enteric nervous system?consists of some one hundred million?neurons[31]?that are embedded in the?peritoneum, the lining of the?gastrointestinal tract?extending from the esophagus to the anus.[32]?These neurons are collected into two?plexuses?- the? HYPERLINK "" \o "Myenteric plexus" myenteric (or Auerbach's) plexus?that lies between the longitudinal and the smooth muscle layers, and the? HYPERLINK "" \o "Submucosal plexus" submucosal (or Meissner's) plexus?that lies between the circular smooth muscle layer and the mucosa.[33][34][35]Parasympathetic innervation?to the?ascending colon?is supplied by the? HYPERLINK "" \o "Vagus nerve" vagus nerve.?Sympathetic innervation?is supplied by the? HYPERLINK "" \o "Splanchnic nerves" splanchnic nerves?that join the?celiac ganglia. Most of the digestive tract is innervated by the two large celiac ganglia, with the upper part of each ganglion joined by the?greater splanchnic nerve?and the lower parts joined by the?lesser splanchnic nerve. It is from these ganglia that many of the?gastric plexuses?arise.Nervous systemThe nervous system is a complex network of nerves and cells that carry messages to and from the brain and spinal cord to various parts of the body.The nervous system includes both the Central nervous system and Peripheral nervous system. The Central nervous system is made up of the brain and spinal cord and The Peripheral nervous system is made up of the Somatic and the Autonomic nervous systems.The Central Nervous System (CNS)The central nervous system is divided into two major parts: the brain and the spinal cord.The BrainThe brain lies within the skull and is shaped like a mushroom.? The brain consists of four principal parts:the brain stemthe cerebrumthe cerebellumthe diencephalonThe brain weighs approximately 1.3 to 1.4 kg. It has nerve cells called the neurons and supporting cells called the glia.There are two types of matter in the brain:? grey matter and white matter.? Grey matter receives and stores impulses.? Cell bodies of neurons and neuroglia are in the grey matter.? White matter in the brain carries impulses to and from grey matter.? It consists of the nerve fibers (axons).The Brain StemThe brain stem is also known as the Medulla oblongata. It is located between the pons and the spinal cord and is only about one inch long.The CerebrumThe cerebrum forms the bulk of the brain and is supported on the brain stem.? The cerebrum is divided into two hemispheres.? Each hemisphere controls the activities of the side of the body opposite that hemisphere.The hemispheres are further divided into four lobes:Frontal lobeTemporal lobesParietal lobeOccipital lobeThe CerebellumThis is located behind and below the cerebrum.The DiencephalonThe diencephalon is also known as the fore brain stem. It includes the thalamus and hypothalamus. The thalamus is where sensory and other impulses go and coalesce.The hypothalamus is a smaller part of the diencephalonOther Parts of the BrainOther parts of the brain include the midbrain and the pons:the midbrain provides conduction pathways to and from higher and lower centersthe pons acts as a pathway to higher structures;? it contains conduction pathways between the medulla and higher brain centersThe Spinal CordThe spinal cord is along tube like structure which extends from the brain. The spinal cord is composed of a series of 31 segments.? A pair of spinal nerves comes out of each segment.? The region of the spinal cord from which a pair of spinal nerves originates is called the spinal segment.? Both motor and sensory nerves are located in the spinal cord.The spinal cord is about 43 cm long in adult women and 45 cm long in adult men and weighs about 35-40 grams. It lies within the vertebral column, the collection of bones (back bone).Other Parts of the Central Nervous SystemThe meninges are three layers or membranes that cover the brain and the spinal cord.? The outermost layer is the dura mater.? The middle layer is the arachnoid, and the innermost layer is the pia mater. The meninges offer protection to the brain and the spinal cord by acting as a barrier against bacteria and other microorganisms.The Cerebrospinal Fluid (CSF) circulates around the brain and spinal cord. It protects and nourishes the brain and spinal cord.NeuronsThe neuron is the basic unit in the nervous system. It is a specialized conductor cell that receives and transmits electrochemical nerve impulses. A typical neuron has a cell body and long arms that conduct impulses from one body part to another body part.Related StoriesResearchers identify B immune cells that promote axon myelination in developing neuronsNew method to rapidly assess severity of head injuries could improve patient careStudy shows structural variations in the brain of transgender individualsThere are three different parts of the neuron:the cell bodydendritesaxonCell Body of a NeuronThe cell body is like any other cell with a nucleus or control center.DendritesThe cell body has several highly branched, thick extensions that appear like cables and are called dendrites.? The exception is a sensory neuron that has a single, long dendrite instead of many dendrites.? Motor neurons have multiple thick dendrites. The dendrite's function is to carry a nerve impulse into the cell body.AxonAn axon is a long, thin process that carries impulses away from the cell body to another neuron or tissue.? There is usually only one axon per neuron.Myelin SheathThe neuron is covered with the Myelin Sheath or Schwann Cells. These are white segmented covering around axons and dendrites of many peripheral neurons. The covering is continuous along the axons or dendrites except at the point of termination and at the nodes of Ranvier.The neurilemma is the layer of Schwann cells with a nucleus. Its function is to allow damaged nerves to regenerate.? Nerves in the brain and spinal cord do not have a neurilemma and, therefore cannot recover when damaged.Types of NeuronNeurons in the body can be classified according to structure and function. According to structure neurons may be multipolar neurons, bipolar neurons, and unipolar neurons:Multipolar neurons have one axon and several dendrites. These are common in the brain and spinal cordBipolar neurons have one axon and one dendrite.? These are seen in the retina of the eye, the inner ear, and the olfactory (smell) area.Unipolar neurons have one process extending from the cell body. The one process divides with one part acting as an axon and the other part functioning as dendrite. These are seen in the spinal cord.The Peripheral Nervous SystemThe Peripheral nervous system is made up of two parts:Somatic nervous systemAutonomic nervous systemSomatic Nervous SystemThe somatic nervous system consists of peripheral nerve fibers that pick up sensory information or sensations from the peripheral or distant organs (those away from the brain like limbs) and carry them to the central nervous system.These also consist of motor nerve fibers that come out of the brain and take the messages for movement and necessary action to the skeletal muscles. For example, on touching a hot object the sensory nerves carry information about the heat to the brain, which in turn, via the motor nerves, tells the muscles of the hand to withdraw it immediately.The whole process takes less than a second to happen. The cell body of the neuron that carries the information often lies within the brain or spinal cord and projects directly to a skeletal muscle.Autonomic Nervous SystemAnother part of the nervous system is the Autonomic Nervous System. It has three parts:the sympathetic nervous systemthe parasympathetic nervous systemthe enteric nervous systemThis nervous system controls the nerves of the inner organs of the body on which humans have no conscious control. This includes the heartbeat, digestion, breathing (except conscious breathing) etc.The nerves of the autonomic nervous system enervate the smooth involuntary muscles of the (internal organs) and glands and cause them to function and secrete their enzymes etc.The Enteric nervous system is the third part of the autonomic nervous system. The enteric nervous system is a complex network of nerve fibers that innervate the organs within the abdomen like the gastrointestinal tract, pancreas, gall bladder etc. It contains nearly 100 million nerves.Neurons in the Peripheral Nervous SystemThe smallest worker in the nervous system is the neuron. For each of the chain of impulses there is one preganglionic neuron, or one before the cell body or ganglion, that is like a central controlling body for numerous neurons going out peripherally.The preganglionic neuron is located in either the brain or the spinal cord. In the autonomic nervous system this preganglionic neuron projects to an autonomic ganglion. The postganglionic neuron then projects to the target organ.In the somatic nervous system there is only one neuron between the central nervous system and the target organ while the autonomic nervous system uses two neuronsReproductive systemThe?reproductive system?or?genital system?is a system of?sex organs?within an? HYPERLINK "" \o "Organism" organismwhich work together for the purpose of?sexual reproduction. Many non-living substances such as fluids,?hormones, and?pheromones?are also important accessories to the reproductive system.[1]?Unlike most?organ systems, the?sexes?of?differentiated?species?often have significant differencesHumans]The?human reproductive system?usually involves?internal fertilization?by?sexual intercourse. During this process, the male inserts his?erect penis?into the?female's?vagina?and?ejaculates?semen, which contains?sperm. The sperm then travels through the vagina and cervix into the?uterus?or?fallopian tubes?for fertilization of the?ovum. Upon successful?fertilization?and implantation,?gestation?of the?fetus?then occurs within the female's uterus for approximately nine months, this process is known as?pregnancy?in humans. Gestation ends with?birth, the process of birth is known as labor. Labor consists of the?muscles?of the uterus contracting, the?cervix dilating, and the baby passing out the vagina (the female genital organ). Human's babies and children are nearly helpless and require high levels of?parental care?for many years. One important type of parental care is the use of the?mammary glands?in the female?breasts?to?nurse?the baby.[4]The female reproductive system has two functions: The first is to produce egg cells, and the second is to protect and nourish the offspring until birth. The male reproductive system has one function, and it is to produce and deposit sperm. Humans have a high level of?sexual differentiation. In addition to differences in nearly every reproductive organ, numerous differences typically occur in?secondary sexual characteristics.MaleThe male reproductive system is a series of organs located outside of the body and around the pelvic region of a?male?that contribute towards the reproduction process. The primary direct function of the male reproductive system is to provide the male sperm for fertilization of the ovum.The major reproductive organs of the male can be grouped into three categories. The first category is sperm production and storage. Production takes place in the?testes?which are housed in the temperature regulating?scrotum, immature sperm then travel to the? HYPERLINK "" \o "Epididymis" epididymisfor development and storage. The second category are the ejaculatory fluid producing glands which include the?seminal vesicles,?prostate, and the?vas deferens. The final category are those used for copulation, and deposition of the?spermatozoa?(sperm) within the female, these include the?penis,?urethra,?vas deferens, and?Cowper's gland.Major secondary sexual characteristics includes: larger, more muscular stature, deepened voice,?facial?and?body hair, broad shoulders, and development of an? HYPERLINK "" \o "Adam's apple" adam's apple. An important sexual hormone of males is?androgen, and particularly?testosterone.The testes release a hormone that controls the development of sperm. This hormone is also responsible for the development of physical characteristics in men such as facial hair and a deep voice.The human female reproductive system is a series of organs primarily located inside of the body and around the?pelvic?region of a? HYPERLINK "" \o "Female" femalethat contribute towards the?reproductive?process. The human female reproductive system contains three main parts: the?vulva, which leads to the vagina, the vaginal opening, to the uterus; the?uterus, which holds the developing fetus; and the?ovaries, which produce the female's ova. The?breasts?are involved during the parenting stage of reproduction, but in most classifications they are not considered to be part of the female reproductive system.Vagina]The?vagina?is a fibromuscular (made up of fibrous and muscular tissue)?canal?leading from the outside of the body to the? HYPERLINK "" \o "Cervix" cervixof the?uterus?or womb. It is also referred to as the birth canal in the context of?pregnancy. The vagina accommodates the male?penis?during?sexual intercourse.?Semen?containing?spermatozoa?is?ejaculated?from the male at?orgasm, into the vagina potentially enabling?fertilization?of the?egg cell?(ovum) to take place.CervixThe cervix is the?neck?of the uterus, the lower, narrow portion where it joins with the upper part of the vagina. It is?cylindrical?or?conical?in shape and protrudes through the upper anterior vaginal wall. Approximately half its length is visible, the remainder lies above the vagina beyond view. The vagina has a thick layer outside and it is the opening where the fetus emerges during delivery.UterusThe?uterus?or womb is the major female reproductive?organ. The uterus provides mechanical protection, nutritional support, and waste removal for the developing embryo (weeks 1 to 8) and fetus (from week 9 until the delivery). In addition, contractions in the muscular wall of the uterus are important in pushing out the fetus at the time of birth.The uterus contains three suspensory ligaments that help stabilize the position of the uterus and limits its range of movement. The uterosacral ligaments keep the body from moving inferiorly and anteriorly. The round ligaments restrict posterior movement of the uterus. The cardinal ligaments also prevent the inferior movement of the uterus.The uterus is a pear-shaped?muscular?organ. Its major function is to accept a fertilized ovum which becomes implanted into the? HYPERLINK "" \o "Endometrium" endometrium, and derives nourishment from blood vessels which develop exclusively for this purpose. The fertilized ovum becomes an?embryo, develops into a?fetus?and gestates until?childbirth. If the egg does not embed in the wall of the uterus, a female begins?menstruation.Fallopian tubeThe Fallopian tubes are two tubes leading from the ovaries into the uterus. On maturity of an ovum, the follicle and the ovary's wall rupture, allowing the ovum to escape and enter the Fallopian tube. There it travels toward the uterus, pushed along by movements of?cilia?on the inner lining of the tubes. This trip takes hours or days. If the ovum is fertilized while in the Fallopian tube, then it normally implants in the? HYPERLINK "" \o "Endometrium" endometrium?when it reaches the uterus, which signals the beginning of?pregnancy.OvariesThe ovaries are small, paired organs located near the lateral walls of the pelvic cavity. These organs are responsible for the production of the?egg cells?(ova) and the secretion of hormones. The process by which the egg cell (ovum) is released is called?ovulation. The speed of ovulation is?periodic?and impacts directly to the length of a?menstrual cycle.After ovulation, the egg cell is captured by the Fallopian tube, after traveling down the Fallopian tube to the uterus, occasionally being fertilized on its way by an incoming sperm. During fertilization the egg cell plays a role; it releases certain molecules that are essential to guiding the sperm and allows the surface of the egg to attach to the sperm's surface. The egg can then absorb the sperm and fertilization can then begin.[ HYPERLINK "" \o "Wikipedia:Citation needed" citation needed]?The Fallopian tubes are lined with small hairs (cilia) to help the egg cell travel.DevelopmentChromosome characteristics determine the genetic sex of a fetus at?conception. This is specifically based on the 23rd pair of chromosomes that is inherited. Since the mother's egg contains an X chromosome and the father's sperm contains either an X or Y?chromosome, it is the male who determines the fetus's sex. If the fetus inherits the X chromosome from the father, the fetus will be a female. In this case,?testosterone?is not made and the? HYPERLINK "" \o "Wolffian duct" Wolffian duct?will degrade thus, the? HYPERLINK "" \o "Müllerian duct" Müllerian ductwill develop into female sex organs. The?clitoris?is the remnants of the Wolffian duct. On the other hand, if the fetus inherits the Y chromosome from the father, the fetus will be a male. The presence of testosterone will stimulate the Wolffian duct which will bring about the development of the male sex organs and the Müllerian duct will degrade.[2]PhysiologyThe reproductive tract (or genital tract) is the?lumen?that starts as a single pathway through the vagina, splitting up into two lumens in the uterus, both of which continue through the Fallopian tubes, and ending at the?distal ostia?that open into the?abdominal cavity.In the absence of fertilization, the ovum will eventually traverse the entire reproductive tract from the fallopian tube until exiting the vagina through?menstruation.The reproductive tract can be used for various? HYPERLINK "" \o "Transluminal procedure" transluminal procedures?such as? HYPERLINK "" \o "Fertiloscopy" fertiloscopy,?intrauterine insemination?and transluminal?sterilization.Clinical significanceVaginitis[Vaginitis?is inflammation of the vagina and largely caused by an infection. It is the most common gynaecological condition presented. It is difficult to determine any one organism most responsible for vaginitis because it varies from range of age, sexual activity, and method of microbial identification. Vaginitis is not necessarily caused by a?sexually transmitted infection?as there are many infectious agents that make use of the close proximity to mucous membranes and secretions. Vaginitis is usually diagnosed based on the presence of vaginal discharge, which can have a certain color, odor, or quality.[3]Bacterial vaginosis]This is a vaginal infection in women. It is differs from vaginitis in that there is no inflammation. Bacterial vaginosis is polymicrobial, consisting of many?bacteria?species. The diagnosis for bacterial vaginosis is made if three of the following four criteria are present: (1) Homogenous, thin discharge, (2) a?pH?of 4.5 in the vagina, (3)?epithelial cells?in the vagina with bacteria attached to them, or (4) a fishy odor. It has been associated with an increased risk of other genital tract infections such as? HYPERLINK "" \o "Endometritis" endometritis.[3]Yeast infectionThis is a common cause of vaginal irritation and according to the?Centers for Disease Control and Prevention?at least 75% of adult women have experienced one at least once in their lifetime. Yeast infections are caused by an overgrowth of fungus in the vagina known as?Candida. Yeast infections are usually caused by an imbalance of the pH in the vagina, which is usually acidic. Other factors such as pregnancy, diabetes, weakened immune systems, tight fitting clothing, or?douching?can also be a cause. Symptoms of yeast infections include itching, burning, irritation, and a white cottage-cheese-like discharge from the vagina. Women have also reported that they experience painful intercourse and urination as well. Taking a sample of the vaginal secretions and placing them under a microscope for evidence of yeast can diagnose a yeast infection. Treatment varies from creams that can be applied in or around the vaginal area to oral tablets that stop the growth of fungus.[3]Genital mutilationThere are many practices of mutilating female genitalia in different cultures. The most common two types of genital mutilation practiced are? HYPERLINK "" \o "Clitoridectomy" clitoridectomy, the circumcision of the clitoris and the excision of the?prepuce?the skin around the clitoris. They can all involve a range of adverse health consequences such as?bleeding, irreparable tissue damage, and?sepsis?which can sometimes prove fatal.Genital surgeryGenitoplasty?refers to surgery that is carried out to repair damaged sex organs particularly following cancer and its treatment. There are also?elective surgicalprocedures which change the appearance of the external genitals.Reproductive rightsThe?International Federation of Gynaecology and Obstetrics?was founded in 1954 to promote the well-being of women particularly in raising the standards of gynaecological practice and care. As of 2010 there were 124 countries involved.Reproductive rights?are legal rights related to reproduction and?reproductive health. Women have the right to control matters involving their sexuality including their sexual and reproductive health. Violation of these rights include forced pregnancy, forced sterilization, forced abortion and?genital mutilation. Female genital mutilation is the complete or partial removal of a female's external?genitals.Male Reproductive System OrgansThe male reproductive system consists of sexual organs, accessory glands, and a series of duct systems that provide a pathway for fertile sperm cells to exit the body.Penis?- Main organ involved in sexual intercourse. This organ is composed of erectile tissue,?connective tissue, and?skin. The urethra extends through the length of the penis, allowing urine and sperm to pass.Testes?- Male primary reproductive structures that produce male gametes (sperm) and sex?hormones.Scrotum?- External pouch of skin that contains the testes. Because the scrotum is located outside of the abdomen, it can reach temperatures that are lower than that of internal body structures. Lower temperatures are necessary for proper sperm development.Epididymis?- System of ducts that receive immature sperm from the testes. Its function is to develop immature sperm and to house mature sperm.Ductus Deferens or Vas Deferens?- Fibrous, muscular tubes that are continuous with the epididymis and provide a pathway for sperm to travel from the epididymis to the urethraEjaculatory Duct?- Duct formed from the union of the ductus deferens and seminal vesicles. Each ejaculatory duct empties into the urethra.Urethra?- Tube that extends from the urinary bladder through the penis. This canal allows for the excretion of reproductive fluids (semen) and urine from the body. Sphincters prevent urine from entering the urethra while semen is passing through.Seminal Vesicles?- Glands that produce fluid to nurture and provide energy for sperm cells. Tubes leading from the seminal vesicles join the ductus deferens to form the ejaculatory duct.Prostate Gland?- Gland that produces a milky, alkaline fluid which increases sperm motility. The contents of the prostate empty into the urethra.Bulbourethral or Cowper's Glands?- Small glands located at the base of the penis. In response to sexual stimulation, these glands secrete an alkaline fluid which helps to neutralize acidity from urine in the urethra and acidity in the vagina.Similarly, the female reproductive system contains organs and structures that promote the production, support, growth, and development of female gametes (egg cells) and a growing fetus.Reproductive System: Gamete ProductionGametes are produced by a two-part cell division process called?meiosis. Through a sequence of steps, the?replicated DNA?in a parent cell is distributed among four?daughter cells. Meiosis produces gametes with one half the number of? HYPERLINK "" chromosomesas the parent cell. Because these cells have one half the number of chromosomes as the parent cell, they are called?haploid?cells. Human sex cells contain one complete set of 23 chromosomes. When sex cells unite at?fertilization, the two haploid cells become one?diploid?cell that contains 46 chromosomes.The production of sperm cells is known as?spermatogenesis. This process occurs continuously and takes place within the male testes. Hundreds of millions of sperm must be released in order for fertilization to take place.?Oogenesis?(ovum development) occurs in the female ovaries. In?meiosis I?of oogenesis, daughter cells are divided asymmetrically. This asymmetrical cytokinesis results in one large egg cell (oocyte) and smaller cells called polar bodies. The polar bodies degrade and are not fertilized. After meiosis I is complete, the egg cell is called a secondary oocyte. The haploid secondary oocyte will only complete the second meiotic stage if it encounters a sperm cell and fertilization begins. Once fertilization is initiated, the secondary oocyte completes?meiosis II?and is then called an ovum. The ovum fuses with the sperm cell, and fertilization is complete. The fertilized ovum is called a zygote.Extraocular Muscles:There are six muscles that are present in the orbit (eye socket) that attach to the eye to move it. These muscles work to move the eye up, down, side to side, and rotate the eye.The superior rectus is an extraocular muscle that attaches to the top of the eye. It moves the eye upward. The inferior rectus is an extraocular muscle that attaches to the bottom of the eye. It moves the eye downward. The medial rectus is an extraocular muscle that attaches to the side of the eye near the nose. It moves the eye inward toward the nose. The lateral rectus is an extraocular muscle that attaches to the side of the eye near the temple. It moves the eye outward.The superior oblique is an extraocular muscle that comes from the back of the orbit. It travels through a small pulley (the trochlea) in the orbit near the nose and then attaches to the top of the eye. The superior oblique rotates the eye inward around the long axis of the eye (front to back). The superior oblique also moves the eye downward.The inferior oblique is an extraocular muscle that arises in the front of the orbit near the nose. It then travels outward and backward in the orbit before attaching to the bottom part of the eyeball. It rotates the eye outward along the long axis of the eye (front to back). The inferior oblique also moves the eye upward.Conjunctiva:The conjunctiva is a transparent mucous membrane that covers the inner surface of the eyelids and the surface of the eye.? When it is inflamed or infected it becomes red or pink.? This is called conjunctivitis or “pinkeye”.Lacrimal Gland:The lacrimal gland produces tears that lubricate the eye. It is located under the lateral edge of the eyebrow in the orbit.Tenon’s Capsule:Tenon’s capsule is a layer of tissue that lies between the conjunctiva and the surface of the eye.Sclera:The sclera is the white outer wall of the eye. It covers nearly the entire surface of the eyeball. It is a strong layer made of collagen fibers. The tendons of the six extraocular muscles attach to the sclera.Cornea:The cornea occupies the front center part of the outer wall of the eye. It is made of collagen fibers in a very special arrangement so that the cornea is clear. One looks through the cornea to see the iris and pupil. The cornea bends light coming into the eye so that it is focused on the retina.? The cornea is the part of the eye on which contact lenses are placed.Internal (Intraocular)Anatomy?Anterior chamber:The anterior chamber is a fluid (aqueous humor) filled space inside the eye. The cornea lies in front of the anterior chamber, and the iris and the pupil are behind it.Iris/Pupil:The iris is the colored part of the eye. It is disc shaped with a hole in the middle (the pupil). Muscles in the iris cause the pupil to constrict in bright light and to dilate in dim light. The change in pupil size regulates the amount of light that reaches the posterior (back) part of the eye.Lens:The lens of the eye is located directly behind the pupil. The lens bends light coming into the eye to help focus it on the retina. It changes shape to help the eye focus to see objects clearly at near. The lens is suspended from the wall of the eye by many small fibers (zonules) that attach to its capsule.Ciliary Body:The ciliary body is attached to the outer edge of the iris near the wall of the eye. The ciliary body produces the fluid (aqueous humor) that fills the eye and nourishes its structures. It also helps to change the shape of the lens when focusing occurs.Vitreous:The vitreous cavity lies between the lens and the retina and fills 4/5 of the space inside the back part of the eye. A gelatinous substance known as the vitreous humor fills the cavity.? This plays an important role in nourishing the inner structures of the eye. Light comes into the eye through the pupil and passes through the vitreous to be projected on the retina.Retina:The retina is a thin, transparent structure that covers the inner wall of the eye. The eye works like a camera, and the retina is similar to the film in the camera. It is where images are first projected before they are transmitted through the optic nerve to the brain. It is a very complex structure with 10 layers of specialized cells including the photoreceptor cells (rods and cones).Photoreceptors:Photoreceptors are highly specialized cells of the retina that receive light impulses and change them into chemical energy that can be transmitted by nerve cells to the brain. The two types of photoreceptors are rods and cones. Rods perceive black and white and serve night vision primarily. Cones are responsible for color perception and central vision.Macula:The macula is a small, specialized area of the retina that has very high sensitivity and is responsible for central vision.Retinal Pigment Epithelium (RPE):The retinal pigment epithelium is a layer of cells deep in the retina. This single layer of cells helps maintain the function of the photoreceptor cells in the retina by processing vitamin A products, turning over used photoreceptor segments, absorbing light, and transporting nutrients in and out of the photoreceptor cells.Choroid:The choroid is a tissue layer that lies between the retina and the sclera. The choroid has a rich supply of blood vessels that nourish the retina.Uveal Tract:The uveal tract is a pigmented component of the eye that is comprised of 1) the iris, 2) the ciliary body, and 3) the choroid.Optic Nerve:The optic nerve connects each eye to the brain. It is a structure that sends the picture seen by the eye to the brain so that they can be processed. The optic nerves end in a structure called the optic chiasm. In an adult, the optic nerve is about the diameter of a pencil. There are over 1 million individual nerve cells in the optic nerveOptic Chiasm:The optic chiasm is the place in the brain where the two optic nerves meet. The individual nerve fibers from each nerve are sorted in the chiasm. The sorting occurs in such a way that the right side of the brain controls the view of objects in left visual space and the left side of the brain controls the view of objects in right visual space [See figure 3].Visual Cortex:This is an area of the brain in the posterior occipital lobe to which the neurons in the retina ultimately give visual information. The visual cortex helps to process information regarding the image such as its color, composition, and relation in space to other objects. This information is then sent to other parts of the brain that serve higher visual functions. ................
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