CHAPTER 5: THE INTEGUMENTARY SYSTEM



STRUCTURE OF THE SKIN: Know your diagrams, micrographs & modelsOVERVIEWCutaneous membrane (skin): The skin is the largest organ of the body based on weight and surface area. Epidermis:Thin layer located superficial to the dermisComposed of keratinized stratified squamous epithelium Has 4 - 5 sublayers: depending on locationDermis:thick layer located deep to the epidermiscomposed of areolar connective tissue (papillary region)reticular connective tissue & dense irregular connective tissue (reticular region).Contains capillary loops (very vascular) & nerve receptorsHypodermis (subcutaneous (subQ) layer; superficial fascia):located deep to the dermiscomposed of adipose and areolar connective tissuesProteins fibers from the dermis extend into the hypodermis, which anchor the dermis to this layer. The hypodermis stores fat, acts as an energy reserve, contains large blood vessels to provide the dermis with nutrients and remove waste products, and contains Pacinian corpuscles to detect deep pressure.EPIDERMIS:Four main cell types:Keratinocytes: Approximately 90% of all epidermal cellsform 4 or 5 distinct layers produce keratintough, fibrous protein that functions to :protect tissues from heat, chemicals, and microbesprovides a water-repellant barrier that decreases water loss/gain from the bodyInhibits the entry of microbes and foreign substances.Melanocytes:functions to produce melaninPigment that provides yellow-red to brown-black coloring of the skin. Phagocytized by keratinocytes – accumulates on superficial side of nucleus - absorbs ultraviolet (UV) radiation from the sun - protect DNA from mutation from UV radiationLangerhans cells (epidermal dendritic cells): specialized macrophages that originate in the red bone marrow and migrate to the epidermis function to initiate immune responses against microbes that invade the skinEasily damaged by UV radiation.Merkel cells: least numerous of the epidermal cellslocated in the stratum basaleMake contact with neurons to detect different aspects of touch.Sub-layers of epidermis: From deep to superficial: distinct layers of keratinocyte development.Stratum basale (basal layer): single layer of mostly columnar keratinocytes; many of which are stem cellsundergo constant somatic cell division (highly mitotic)site of Merkel’s cells & melanocytes (25% of cells are melanocytes)basement membrane connects to dermis with hemidesmosomesStratum spinosum (prickly layer): 8-10 layers of living keratinocytesAlso mitotic (although less so than basale)weblike networks of intermediate tonofilaments that function resist tension and provide strength and flexibility to the epidermis.Contain Langerhan’s cellsStratum granulosum (granular layer): 3-5 layers of keratinocytesContain Langerhan’s cellsundergo apoptosis via keratinizationproduction of keratohyalin granules - accumulates in the cytoplasm and kills the cells These dead keratinocytes provide a physical protective barrier and a water-repellant seal to the epidermisthis layer marks the transition between the living and dead cells of the epidermiscells begin to die due to avascularity of epithelium and keratinization (Be able to explain why this is so)Stratum lucidum (clear layer):only located in the thick skin of the fingertips, palms, and soles of the feet3-5 layers of flat, clear, dead keratinocytes - completely keratinized & deadKeratohyalin granules & tonofilaments form keratin fibrils provide addition protection to areas of the epidermis exposed to great frictionStratum corneum (horn layer): 25-30 layers of flat, dead keratinocytes – completely keratinized & deadKeratohyalin granules & tonofilaments form keratin fibrils Continuously shed from the body and constantly replaced by cells from the deeper layers. When an area of the stratum corneum is exposed to constant friction, a callus can form, which is abnormal thickening of this layer.Thin skin: Thin skin of the epidermis includes the stratum basale, stratum spinosum, stratum granulosum, and stratum corneum.Thick skin: Thick skin of the epidermis includes all of the epidermal layers (stratum basale, stratum spinosum, stratum granulosum, stratum lucidum, and stratum corneum), and it’s located in the skin of the fingertips, palms, and soles of the feet, where friction is the greatest.3683007683500DERMIS COMPOSITION:Hairsebaceous glandssudoriferous glandsarrector pili musclesblood vesselsnerve endings (receptors).SUB-LAYERS of dermis:Papillary regioncomposed of areolar connective tissue with many fine elastic fibersSA is increased due to the dermal papillae extension into the epidermis small, fingerlike projections of the papillary regionEach dermal papilla contains capillary loops (subpapillary plexuses), Meissner corpuscles, and free-nerve endings.Capillary loops (subpapillary plexuses): supply oxygen, nutrients & remove wastes – vital to body temperature homeostasisMeissner corpuscles: encapsulated nerve endings that function as tactile receptors to detect touch.Free-nerve endings: bare dendrites of neurons that function to detect temperature, pain, itch, and tickle.Friction ridges: skin ridges comprised of epidermal and dermal ridges (dermal papillae are located on top of the dermal ridges)located on the palms of the hands and soles of the feetpatterns are unique & genetically determinedfunction to increase friction and enhance the grasping ability Sweat pores are located on the crests of friction ridges, and fingerprints result when the anterior aspects of our fingers leave sweaty films on objects we touch.Reticular region: composed of reticular connective tissue & of dense irregular connective tissue with fibroblasts, collagen fibers, and elastic fibers. About 80% of the dermisdermal structures of the skin (i.e. hair bulbs, hair follicles, glands, arrector pili muscles, blood vessels, and nerve endings) are located here.Properties:Extensibility: skin’s ability to stretch due to the collagen and elastic fibers in the dermis.Elasticity: skin’s ability to recoil due to the collagen and elastic fibers in the dermis.Striae: stretch marks resulting from extreme stretching of the skin producing small tears in the collagen bundles of the dermis.STRUCTURAL BASIS OF SKIN COLORMelanin: Melanin is a pigment produced by melanocytes that colors the skin from pale yellow to red to tan to black. Skin color varies depending on the amount of melanin produced by the melanocytes. Freckles, which are congenital, and “sun spots”, which are acquired over time due to exposure to the sun, are an accumulation of melanin in a concentrated area(s) of the skin.Hemoglobin: Hemoglobin is the iron-containing, oxygen-carrying pigment of erythrocytes (red blood cells), and it provides a red color to the skin because of its iron content. The amount of red color depends on the amount of blood flowing through the capillaries in the dermis.Carotene: Carotene is a yellow-orange pigment that functions as a precursor to the anabolism of Vitamin A (molecule used to synthesize the retinal pigments for vision). Carotene accumulates in the stratum corneum and in the adipose tissue in the dermis and hypodermis when excessive dietary intake of this molecule occurs. If excessive amounts of carotene-rich foods are eaten in a short time period, light-skinned individuals can appear orange due to the accumulation of carotene in the skin.APPENDAGES OF THE SKINSkin glands: exocrine glands composed of glandular epithelium, which produce and secrete specific substances and release these substances onto the surface of cover and lining epithelium.Sebaceous (oil) glands: connected to hair folliclesproduce and secrete sebumcomposed of triglycerides, cholesterol, proteins, and saltscover the hair shaft and epidermal surface to prevent drying of these structures, to prevent water loss/gain from the body, to help keep the epidermal surface soft and pliable, and to inhibit the growth of bacteria on the epidermal surface.become active during puberty when androgen synthesis increases.Sudoriferous (sweat) glands:composed of specialized secretory cells called myoepithelial cells, which contract when stimulated by the autonomic nervous system, and function to produce and secrete sweat onto the epidermal surface.Merocrine (eccrine) sweat glands:most common and abundant sweat glands (about 3 million per person)numerous in the skin of the forehead, palms, and soles of the feet, and are not located in the skin of the nipples and external genitalsproduce and secrete a hypotonic filtrate (sweat) formed from blood plasma. This filtrate is composed of approximately 99% water and 1% salts, vitamin C, antibodies, dermcidin (microbe-killing peptide), metabolic waste products (urea, uric acid, ammonia, bilirubin, etc.), and some drug metabolites. It passes through the myoepithelial cells of the gland and is released from the cells via exocytosis. When the hypotonic filtrate is released from these glands, it cools the skin’s surface via evaporative cooling.Apocrine sweat glands:located in the skin of the axilla, groin, areolae of the breasts, and the bearded regions of adult male facesbegin to function at puberty when androgen synthesis begins, and the sweat released from these glands is the same as merocrine secretions with added fatty acids and proteins. This sweat is the source of body odor via bacteria wastesThe secretory cells, also, release this sweat via exocytosis. Although their specific function is unknown, it’s believed that these glands may be the sexual scent glands in humans even though apocrine secretions are odorless (pheromones).Ceruminous glands:modified apocrine sweat glands located in the skin of the external auditory canalproduce and secrete cerumen, a waxy substance that impedes the entry of foreign material into the ear.Hair (pili): composed of dead, keratinized cells, and present on most skin surfaces, except the fingertips, palms, and soles of the feetfunctions to protect the skin’s surface from physical trauma, heat loss, and sunlight, and it prevents the entry of foreign matter into our eyes and nosedetects tactile sensations on the skin’s surface.Hair shaft:superficial portion of the hair that extends above the skin’s surfacecomposed of dead, keratinized cellsstructure of the hair shaft determines the hair type. Round hair shafts produce straight hair, oval hair shafts produce wavy hair, and ribbon-like hair shafts produce kinky hair.Hair root: deep portion of the hair located in the dermiscomposed of active keratinocytes that will, eventually, undergo apoptosis via keratinizationcomposed of a medulla (central area composed of large cells and air spaces), a cortex (layer composed of several flat cells surrounding the medulla), and a cuticle (outermost layer composed of a single layer of overlapping keratinized cells that function to provide strength to the hair and keep medulla and cortex tightly compacted).Hair follicle:an epithelial and connective tissue covering surrounding the hair rootcomposed of dermal and epithelial root sheaths.Dermal (connective tissue) root sheath: superficial covering of the hair follicle, and it’s derived from dermal connective tissue.Epithelial root sheath: located deep to the dermal root sheath, and it’s derived from an invagination of epithelial tissue from the epidermis. This thickness of this covering decreases as it approaches the hair bulb, and only a single layer of cells covers the hair papilla.Hair bulb: The hair bulb is an onion-shaped structure located at the base of each hair follicle, and it’s composed of areolar connective tissue and blood capillaries to nourish the growing hair and hair follicle.Hair papilla: The hair papilla is dermal tissue that projects into the hair bulb, and it contains blood capillaries that provide nutrients and remove wastes from the growing hair and signals hair growth.Hair matrix: The hair matrix is a single layer of stem cells located at the tip of the hair papilla, which functions to undergo somatic cell division to allow the hair to grow. These actively dividing cells receive chemical signals from the hair papilla, which trigger the cell division process.Arrector pili muscle: The arrector pili muscle is a bundle of smooth muscle fibers, located in the dermis that attaches to the dermal root sheath of hair follicles. When it contracts, it functions to force sebum out of sebaceous glands and pulls the hair shaft perpendicular to the skin’s surface.Hair root (root hair) plexuses: Hair root plexuses are nerve endings (bare neuronal dendrites) that surround the dermal root sheath of each hair follicle, and they function to detect tactile sensations.Nails: Nails are scale-like modifications of the epidermis composed of tightly-packed, hard, dead, keratinized epithelial cells. They form clear solid coverings over the dorsal surfaces of the digits, which functions to protect the digits, grasp objects, and scratch areas of the body.Nail body: The nail body is the visible portion of the nailFree edge: The free edge is the distal part of the nail that extends over the end of the digit.Nail root: The nail root is the proximal portion of the nail embedded in the epidermis and dermis.Nail bed: The nail bed is the epidermal area located deep to the nail, and the proximal thickened area of the nail bed, deep to the nail root, contains the nail matrix.Nail matrix: The nail matrix is composed of stem cells that undergo somatic cell division, which functions to produce new keratinized cells to allow the nail to grow.FUNCTIONS OF THE INTEGUMENTARY SYSTEMProtection: The ability of skin to protect underlying tissues from mechanical stress, pathogens, heat, chemicals, UV radiation, and decreases water loss/gain and inhibits bacterial growth from the skin’s surface.Chemical barriers: Protection is provided by the chemical barriers of the skin, which include “protective” secretions and melanin. The acid mantle refers to the acidic secretions of the skin, which inhibit bacterial growth on the skin’s surface. Bacterial growth is, also, inhibited and controlled by natural antibiotics called defensins produced by skin cells, dermcidin in sweat, and sebum produced by sebaceous glands. In addition, melanin is a pigment that absorbs UV radiation to protect skin cells from damage caused by this type of electromagnetic radiation.Physical/Mechanical barriers: Protection is provided by the physical/mechanical barriers of the keratinized epithelial cells that compose the epidermis. In addition, the epidermal surface is covered with sebum and glycolipids, which inhibits osmosis and the diffusion of water-soluble substances across its surface. However, lipid-soluble substances, like oxygen, carbon dioxide, lipid-soluble vitamins (i.e. vitamin A, D, E, and K), plant chemicals (i.e. oleoresins), and organic solvents (i.e. acetone and paint thinners) can penetrate the skin.Biological barriers: Protection is provided by biological barriers, which include Langerhans cells in the epidermis, macrophages in the dermis, and DNA. Langerhans cells respond to antigens (i.e. pathogens) that present themselves in the epidermis, and macrophages phagocytize pathogens (i.e. bacteria and viruses) that penetrate the epidermis and dermis. Like melanin, DNA protects the skin against UV radiation as the electrons in DNA absorb the radiation and transfer it to the atomic nuclei, which release it as heat.Thermoregulation: The ability of skin to regulate body temperature via evaporative cooling by releasing sweat onto the skin’s surface and via vasodilation in the dermis to adjust blood flow in the skin.Cutaneous sensation: The ability of skin to detect tactile sensations (touch, pressure, vibration, itch, and tickle) and thermal sensations due to the sensory receptors and nerve endings located in the dermal layer of the skin.Metabolic functions: The skin is capable of synthesizing various molecules for biochemical processes.Vitamin D synthesis: The ability of skin to synthesize vitamin D precursors from modified cholesterol molecules by absorbing UV radiation from sunlight. These molecules enter the blood supply and circulate to all areas of the body, where they will be converted into vitamin D.Epidermal metabolism: Epidermal cells are, also, capable of performing various metabolic functions. For example, keratinocyte enzymes can inhibit some cancer-causing chemicals that penetrate the skin and can metabolize steroid hormones, like transforming cortisone into hydrocortisone. Some skin cells can synthesize important proteins, like collagenase, which is an enzyme involved in the catabolism of collagen and helps deter the production of wrinkles.Blood reservoir: The dermis contains an extensive blood supply (5-10% of the total blood volume in the body) due to an abundance of blood vessels located in this layer.Excretion: The ability of skin to eliminate substances from the body, such as metabolic wastes (i.e. urea, uric acid, ammonia, and bilirubin) and drug metabolites.To improve your knowledge & understanding of the concepts (which will improve your exam scores): You must be very systematic & purposeful & intentional about your study habits.Set the amount of time that you are choosing to study – during that time:TURN YOUR PHONE OFF, TURN THE TV OFF, LISTEN TO MUSIC WITH NO WORDSDO NOT DISCUSS ANYTHING BUT WHAT YOU ARE STUDYING – your brain’s attention will be fragmented if you give it too many things to focus on.Read through each section of notes prior to and after discussion. Use the PPTs to aid your understanding.Know what you are confused about before you get to class.Ask questions during the discussion.Make notes & sketches on your lecture outline as you go over the material.Read through the accompanying section of the book chapter.To learn & practice:Work through the Dynamic Study Modules for the accompanying section.Go to the Study Area, choose the chapter & click GOComplete Steps 1-3 of Chapter GuideListen to the MP3 Tutor SessionsDo the Interactive PhysiologyUse the PAL 3.1 Anatomical Models & Histology sections & flashcards – select the topic you are anize & use flashcards, partner study, concept maps, outlines, etc. to help you memorize & understand the material. Assess yourself so you will know what you know well & what you still need to study – don’t wait till the last minute.There are lots of great video clips on Khan Academy & other sites: you will need to evaluate if they are an appropriate level for you.After you have studied some: Begin your Mastering A&P assignments & complete them before the due plete & Study your Lab Portfolio & have it ready before the due date.Schedule out enough time to study your materials each night – concentrated, consistent repetition is required for memorization – Memorization is required for understanding.Ask for help if you need it. ................
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