Small intestine: - Ms. Petrauskas' Class - Home



Digestion after the StomachSmall intestine:Most digestion and nutrient absorption occurs in the small intestine.The small intestine is a long tube that is only about 2.5cm in diameter and approximately 7 m long. Whereas the large intestine is around 7.6cm in diameter and 1.5m in length.Lipids, carbohydrates, and remaining proteins are digested in the small intestine.It is made up of 3 sections:Duodenum, jejunum, and the ileumDUODENUM: the first 25 to 30 cm. where most enzymes are added and where digestion in the small intestine begins.JEJUNUM: digestion continues and some nutrients are absorbed. ILEUM: where most nutrients are absorbed. Can be distinguished from the jejunum based on shape and size of epithelial cells.Surface Area: the inner surface of the small intestine is adapted to provide the maximum amount of surface area for efficient nutrient absorption.Inner layer is folded into ridges and has many finger like projections called villi (villus)Each villus has even smaller, microscopic projections called microvilliEach villus has a network of blood vessels called capillariesAll nutrients except digested fats, enter the blood stream through the capillariesDigested fats transfer through small vessels called lacteals and transported through the lymphatic systemChemical Digestion in the Small Intestine: Chyme is slowly released into the small intestine at a pH of 2.5.Cholecytokinin (CCK): a hormone secreted by cells in the mucosa of the duodenum and is released into the blood stream. Signals the pancreas to secrete substances to control pH and enzymes to digest carbohydrates, lipids and proteins. Stimulates the release of bileCCK signals the stomach to slow digestionPANCREAS: a long flat gland nestled between the stomach and the duodenum. It secretes enzymes that are critical to the digestive process.Amylase: excreted by the pancreas into the duodenum to break down carbohydratesInsulin: controls glucose levelsLipase: the pancreas also secretes these enzymes that break down fats. Breaks down lipids into shorter chains and into individual fatty acid chains at the surface of fat globules Trypsinogen-Trypsin: the pancreas releases trypsinogen, which is the inactive form of the protein digesting enzyme trypsin (further digests proteins broken down by pepsin). Once in the duodenum, the enzyme called enterokinase converts trypsinogen into active trypsin.Prosecretin-Secretin: Prosecretin is secreted by the lining of the small intestine and is converted to secretin when mixed with the acidic chyme.Secretin: active form, which stimulates pancreatic (bicarbonate ions; HCO3-) and bile secretions.The bicarbonate ions neutralize the hydrochloric acid to a pH of 9Pepsin is inactivated in the basic pHActs a digestive rate regulator and prevents more food from entering from the stomach until digested1133475494030Carboxypeptidase and Erepsin: other protein digesting enzymes that help break down of small protein chains into single amino acidsThe Liver and Gall bladder- secrete to the duodenumThe liver in its digestive functions is considered a gland because it produces and secretes bileBile emulsifies fats, breaking down large fat globules into micelles. This provides a larger surface area for lipases to digestBile is continuously made, but stored in the gall bladder. Fat entering the duodenum stimulates the gall bladder to contract, squeezing the bile through the bile duct and into the duodenumBlood passing through the capillaries of the intestines pass through the liver which also filters toxins such as alcohol. It also stores glycogen and fat soluble vitamins. Diseases of this organ include hepatitis, jaundice, sclerosis and cancer.AbsorptionPassive transport: the movement of materials across a cell membrane without any expenditure of the cell’s energyDiffusion: the movement of molecules from an area of higher concentration to a lower concentration ( move from the small intestines to capillaries, e.g. amino acids)Osmosis: the movement of water from an area of higher concentration to a lower concentration across a selectively permeable membrane (some water content in food is absorbed by osmosis in the stomach and small/large intestine)Facilitated diffusion: the diffusion of molecules across a cell membrane via a transport protein. Each protein has a unique size and shape and only let specific molecules through. (Many of the monosaccharide’s and disaccharide’s move to the capillaries via facilitated diffusion)Active transport: materials are moved across a cell membrane from a lower concentration to a higher concentration using energy provided by the cell. Special protein carriers are embedded in the membrane to carry large molecules and ions across314325240665Diffusion20764500393382576200 Large Intestine1.5m in length and 7.6cm diameterMost of our food has been digested and absorbed except for indigestible material like cellulose. They provide bulk and help us maintain a full feeling for longer. Helps retain water, which helps in elimination of wastes.Water from the leftover matter is absorbed via osmosis as it passes through the colon. When water is removed, feces, the undigested waste, is eliminated from the bodyThe removal of too much water= constipationThe removal of too little water= diarrheaVitamins B and K, sodium Na+, Cl-, are absorbedTakes from 4hrs to 72hrs for undigested material to move through the large intestineThere are more than 500 species of bacteria that inhabit the large intestineE.coli: produce vitamins K and BBi-product of the bacteria is the Production of gas (carbon dioxide, methane and hydrogen sulphideComposed of the CECUM, COLON, RECTUM, ANUSCECUM: the end the large intestine below the opening to the small intestine. A “dead end” that receives processed material from the small intestine. Also contains an opening to the APPENDIXCOLON: longest part of the large intestine and has four segments; the ASCENDING, TRANSVERSE, DESCENDING and SIGMOID colonRECTUM: the last 20cm of the large intestine. Holds waste products of digestion until they are eliminated through the external opening, the anus.Nerves in the wall of the large intestine detect the movement of feces in the rectum and this stimulates the defecation reflex. We are in control of this reflex to a certain degree.1590675396240The internal( smooth muscle and involuntary) and external(skeletal and voluntary) anal sphincters control the process of defecationNausea, Vomiting and DiarrheaNausea: unpleasant feeling associated with the urge to vomit. Your mouth may water, you may break into a cold sweat, look pale and your stomach may feel upset.Emesis (vomiting): a protective mechanism for removing toxins or foreign substances from the body. The expulsion of stomach contents through the esophagus and mouthStrong muscular contractions of the diaphragm and abdominal muscles, force the contents (vomitus) of the stomach upThe gastroesophageal sphincter relaxesBreathing ceases as the larynx and epiglottis close the entrance to the tracheaCauses of vomiting:Symptom of an underlying conditionOccurs in response to a signal from the stomach, intestines, bloodstream, inner ear, or sensory organsExamples:Inner ear: motion sicknessDrugs: chemotherapy, antibiotics, nicotine, alcoholInfections: bacterial (E. coli), viral (stomach flu)Brain: meningitis, migraines, tumorsInjury: concussion, hemorrhageDiseases: gall bladder disease, cancer, ulcersRisks: dehydration, vomitus in respiratory tract causing asphyxiation or infection, tears in the lining of the esophagus and/or strains in abdominal musclesDiarrhea: loose or watery feces as a result of inadequate absorptionAccompanied by upset stomach, stomach pains/cramps and intestinal gasCauses: bacteria (salmonella,E.coli), viruses and parasitesE. coli infections can lead to internal bleeding, severe dehydration, and in severe cases kidney failure (Walkerton water)Colitis: is swelling (inflammation) of the large intestine (colon).Causes: food poisoning, inflammatory disorders (ulcerative colitis, Crohn's colitis) irritable bowel syndrome, lack of blood flow (ischemic colitis) or past radiation to the large intestineSymptoms can include: bloating, gas, bleeding, chills, constant urge to defecate, diarrhea, dehydration, fever and abdominal painFeedback LoopsHormones operate on positive or negative feedback loops:Homeostasis – state of constancy / maintaining an internal steady stateNegative feedback – a change in a physiological variable triggers a response that counteracts the initial changePositive feedback – a change in a physiological variable triggers a response that amplifies the changeExamples of Positive FeedbackChildbirthPressure of baby’s head against sensors near opening of the uterus stimulates uterine contractionsContractions cause greater pressure against the uterine opening which causes stronger contractionsStronger contractions cause even greater pressureEventually allows child to be bornGastrinImpulses from brain (sight, smell, taste of food) stimulate stomach wall to produce gastric juice which begins digestion of food in stomachThen the products of digestions (substances in the food) stimulate the stomach wall to release the hormone gastrin into the circulatory systemAs gastrin recirculates in the bloodstream back to the stomach wall, the hormone stimulates further release of gastric juiceTherefore initial burst of gastric juice is followed by a sustained secretion that continues to add gastric juiceExamples of Negative FeedbackThermostatSet thermostat to 20 ?C (set point)If temperature falls below 20 ?C, the thermostat switches on the heaterWhen thermometer detects that temperature is now above 20 ?C, the thermostat switches the heater offTherefore, change in variable (temperature) triggers mechanism that counteracts the change (cold) to prevent further change in the same direction (more cold)Body Temperature (sweating)Brain detects rise in body temperatureSends nerve impulses to sweat glands to increase the production of sweatSweating lowers body temperature by evaporative cooling(H2O(l) H2O(g) is an endothermic reaction)When body temperature drops below set point then brain stops sending signalsGastrinGastric juice is very acidic (HCl)If the pH of the stomach becomes too acidic (too much gastric juice) the acid will inhibit the release of gastrinThis decreases the production of gastric juice helping the pH to return to normal levels **Therefore Gastrin is an example of both a positive AND a negative feedback loop! ................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download