5. The Integument and Related Structures


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  • 5. The Integument and Related Structures

    1. 1. The Integument and Related Structures
    2. 2. Learning Objectives <ul><li>List the cell types that make up the epidermis and describe the function of each cell type. </li></ul><ul><li>List the five layers of the epidermis. </li></ul><ul><li>Describe the process of keratinization. </li></ul><ul><li>List the structures that constitute the dermis and describe the function of each. </li></ul><ul><li>List the structures of the hypodermis. </li></ul><ul><li>Describe the unique features of the paw pads and planum nasale. </li></ul><ul><li>Describe the parts of the hair follicle and explain how hair grows. </li></ul><ul><li>List and describe the three types of hair. </li></ul><ul><li>Describe the structure and location of sebaceous glands. </li></ul><ul><li>Differentiate between eccrine and apocrine sweat glands. </li></ul>
    3. 3. Integumentary System <ul><li>Skin and related structures: </li></ul><ul><ul><li>Hair, hooves, horns, claws, skin-related glands </li></ul></ul><ul><li>Functions: prevents desiccation; reduces threat of injury; assists in maintaining normal body temperature; excretes water, salt, and organic wastes; receives and conveys sensory information; synthesizes vitamin D; stores nutrients </li></ul>
    4. 4. Integumentary System <ul><li>Consists of three layers: </li></ul><ul><ul><li>Epidermis </li></ul></ul><ul><ul><li>Dermis </li></ul></ul><ul><ul><li>Hypodermis </li></ul></ul>
    5. 5. Epidermis <ul><li>Cell types : </li></ul><ul><li>Keratinocytes – produce keratin, the tough, fibrous, waterproof protein that gives skin its resiliency and strength </li></ul><ul><li>Melanocytes – produce melanin pigment </li></ul><ul><li>Merkel cells – phagocytize microinvaders; macrophage specific to epidermis </li></ul><ul><li>Langerhans cells – found in stratum spinosum; may be involved in allergic and cell-mediated immune response in skin </li></ul>
    6. 6. Epidermal Layers <ul><li>Stratum germinativum (basal layer): </li></ul><ul><li>Deepest layer </li></ul><ul><ul><li>Consists of a single row of keratocytes attached to epithelial basement membrane </li></ul></ul><ul><ul><li>Merkel cells, melanocytes, keratocytes, found in this layer </li></ul></ul>
    7. 7. Epidermal Layers <ul><li>Stratum spinosum (spiny layer): </li></ul><ul><li>Contains several layers of cells held together by desmosomes </li></ul><ul><li>Langerhans cells found in this layer </li></ul>
    8. 8. Epidermal Layers <ul><li>Stratum granulosum (granular middle layer): </li></ul><ul><li>Composed of two to four layers of flattened, diamond-shaped keratocytes that contain lamellated granules of glycolipids </li></ul><ul><li>These glycolipids play a role in helping waterproof the skin and slowing water loss across the epidermis </li></ul>
    9. 9. Epidermal Layers <ul><li>Stratum lucidum </li></ul><ul><li>(clear layer): </li></ul><ul><li>Found in very thick skin </li></ul><ul><li>Composed of a few rows of flattened dead cells </li></ul><ul><li>Contents of the keratogranules combine with intracellular tonofilaments to form keratin fibrils </li></ul>
    10. 10. Epidermal Layers <ul><li>5. Stratum corneum </li></ul><ul><li>(horny outermost layer): </li></ul><ul><li>Composed of 20 to 30 rows of keratocyte “remnants” </li></ul><ul><ul><li>Sometimes called horny or cornified cells </li></ul></ul>
    11. 11. Epidermis of Hairy Skin <ul><li>Hairy skin usually consists of three epidermal layers rather than five (stratum basale, stratum spinosum, and stratum corneum) </li></ul><ul><li>The surface of hairy skin is covered in scalelike folds. </li></ul><ul><li>A knoblike elevation can be seen periodically </li></ul><ul><ul><li>Tactile elevation or epidermal papilla </li></ul></ul><ul><ul><li>Usually associated with a tactile hair (tylotrich hairs) </li></ul></ul>
    12. 12. Dermis <ul><li>Composed of dense irregular connective tissue </li></ul><ul><ul><li>Collagen, elastic, and reticular fibers </li></ul></ul><ul><li>Also includes hair follicles, nerve endings, glands, smooth muscle, blood vessels, and lymphatics </li></ul><ul><li>Fibroblasts, adipocytes, and macrophages also present </li></ul><ul><li>Two layers: </li></ul><ul><ul><li>Papillary layer </li></ul></ul><ul><ul><li>Reticular layer </li></ul></ul>
    13. 13. Dermal Layers <ul><li>Papillary layer </li></ul><ul><li>Underneath the epithelial layer of the epidermis </li></ul><ul><li>Composed of loose connective tissue with loosely woven fibers and ground substance </li></ul><ul><li>Dermal papillae help cement the epidermis and the dermis together </li></ul><ul><li>Blood vessels, pain, temperature, and touch receptors also present </li></ul>
    14. 14. Dermal Layers <ul><li>Reticular layer </li></ul><ul><li>Consists of dense irregular connective tissue </li></ul><ul><li>Bundles of collagen fibers from papillary layer blend into those of reticular layer </li></ul><ul><li>Most fibrous bundles tend to run parallel to each another. </li></ul><ul><li>Separations between bundles represent tension lines in skin </li></ul><ul><li>In areas where a great deal of bending occurs, dermal folds or flexure lines are present. </li></ul>
    15. 15. Hypodermis <ul><li>Composed of areolar tissue containing adipose, blood and lymphatic vessels, and nerves </li></ul><ul><li>Contains special touch receptor – the pacinian corpuscle ( sensitive to heavier pressure than Meissner's corpuscle) </li></ul><ul><li>Fibers of hypodermis are continuous with those of dermis </li></ul><ul><li>Hypodermal layer permits skin to move freely over underlying bone and muscle without putting tension on skin </li></ul>
    16. 16. Special Features of the Integument <ul><li>Pigmentation </li></ul><ul><li>Paw Pads </li></ul><ul><li>Planum Nasale </li></ul><ul><li>Ergots and Chestnuts </li></ul><ul><li>Cutaneous Pouches in Sheep </li></ul>
    17. 17. Pigmentation <ul><li>Result of presence or absence of melanin granules in the extensions of melanocytes </li></ul><ul><ul><li>No pigmentation if granules are concentrated around nucleus of the melanocyte </li></ul></ul><ul><ul><li>As granules move into the cellular extensions and into surrounding tissue, pigmentation becomes macroscopically apparent </li></ul></ul><ul><li>The more granules present, the darker the pigmentation </li></ul>
    18. 18. Pigmentation <ul><li>Melanocyte-stimulating hormone controls dispersion of granules </li></ul><ul><li>Keratocytes arrange melanin on the side of the cell with greatest amount of sun exposure </li></ul><ul><li>Acts to protect keratocytes from exposure to damaging ultraviolet rays </li></ul>
    19. 19. Paw Pads <ul><li>Thick layers of fat and connective tissue with exocrine sweat glands and lamellar corpuscles </li></ul><ul><li>Outer surface is the toughest and thickest skin in the body </li></ul><ul><li>Often pigmented; composed of all five epidermal layers </li></ul><ul><ul><li>Stratum corneum is thicker than all other layers combined </li></ul></ul><ul><li>Conical papillae can be seen covering entire pad </li></ul>
    20. 20. Planum Nasale <ul><li>Top of the nose in cats, pigs, sheep, and dogs </li></ul><ul><li>Planum nasolabiale: the muzzle of cows and horses </li></ul><ul><li>Usually pigmented; aglandular except in sheep, pigs, and cows </li></ul><ul><li>Composed of only three epidermal layers: </li></ul><ul><ul><li>Stratum germinativum, stratum spinosum, stratum corneum </li></ul></ul><ul><ul><li>Not present: stratum lucidum, stratum granulosum </li></ul></ul>
    21. 21. Ergots and Chestnuts <ul><li>Dark horny structures found on the legs of horses, ponies, and other members of the equine family </li></ul><ul><li>Thought to be vestiges of carpal and tarsal pads of second and fourth digits (&quot;splint bones&quot;) </li></ul>
    22. 22. Cutaneous Pouches in Sheep <ul><li>Infoldings of skin </li></ul><ul><li>Infraorbital, interdigital, </li></ul><ul><li>and inguinal pouches </li></ul><ul><li>Contain fine hairs and </li></ul><ul><li>numerous sebaceous </li></ul><ul><li>and oil glands </li></ul><ul><li>Secrete a fatty yellow </li></ul><ul><li>substance which covers </li></ul><ul><li>and sticks to the skin when dry </li></ul>
    23. 23. Related Structures of the Integument <ul><li>Hair </li></ul><ul><ul><li>Hair strands and follicles </li></ul></ul><ul><ul><li>Types of hair </li></ul></ul><ul><li>Glands of the skin </li></ul><ul><ul><li>Sebaceous and sweat glands </li></ul></ul><ul><ul><li>Tail glands </li></ul></ul><ul><ul><li>Anal sacs </li></ul></ul><ul><li>Claws and dewclaws </li></ul><ul><li>Hoof </li></ul><ul><li>Horns </li></ul>
    24. 24. Hair <ul><li>Functions in maintaining body temperature; camouflage </li></ul><ul><li>Hair shaft: visible above the skin </li></ul><ul><li>Hair root: buried within the skin </li></ul><ul><li>Hair follicle: anchors the hair </li></ul><ul><li>Deepest part of hair follicle expands to form a hair bulb </li></ul><ul><li>At the base of the hair bulb is a mound of dermal cells called the papilla. </li></ul><ul><li>Hair strands are formed as epithelial cells mature, fill with keratin, and move away from the papilla. </li></ul>
    25. 25. Hair Follicle <ul><li>Root sheath layers: connective tissue root sheath, external root sheath, and internal root sheath </li></ul><ul><li>Each hair strand is organized into three layers: cuticle, cortex, and medulla </li></ul><ul><li>Root hair plexus: web of sensory nerve endings </li></ul><ul><ul><li>Touch receptor </li></ul></ul>
    26. 26. Growth Cycles of Hair <ul><li>Anagen phase : cells are added at the base of the root, hair lengthens </li></ul><ul><li>Catagen phase : period of transition between anagen and telogen phases </li></ul><ul><li>Telogen phase : maximum length of hair is achieved, hair stops growing, hair follicle shortens, and hair is held in a resting phase </li></ul>
    27. 27. Hair Color <ul><li>Melanocytes transfer melanin to the cortical and medullary cells that form the hair strand. </li></ul><ul><li>Different colors result from the quantity and type of melanin incorporated into the hair. </li></ul><ul><ul><li>Horses produce only one type of melanin; dogs produce two. </li></ul></ul><ul><li>As animals age, melanin production decreases and hair begins to turn gray. </li></ul><ul><li>White hair is formed when the cortex loses its pigment entirely and the medulla becomes completely filled with air. </li></ul>
    28. 28. Types of Hair <ul><li>1. Primary or guard hairs </li></ul><ul><ul><li>Straight or arched; thicker and longer than secondary hairs </li></ul></ul><ul><li>2. Secondary or wool-type hairs </li></ul><ul><ul><li>Softer and shorter than primary hairs; wavy or bristled in the dog; predominant hair type in species with wool-type coats </li></ul></ul><ul><li>3. Tactile (or “sinus”) hairs </li></ul><ul><ul><li>Contain numerous sensory endings </li></ul></ul><ul><ul><li>Commonly known as whiskers; also mixed intermittently throughout the hair coat </li></ul></ul><ul><ul><li>Also called sinus hair because of the large blood sinus located in the connective tissue portion of the follicle </li></ul></ul>
    29. 29. Arrector Pili Muscle <ul><li>Small, smooth muscle </li></ul><ul><li>Attached to each hair follicle </li></ul><ul><li>Innervated by sympathetic nervous system </li></ul><ul><li>Contraction of the muscle pulls the hair to an erect position </li></ul>
    30. 30. Glands of the Skin <ul><li>Sebaceous Glands </li></ul><ul><li>Sweat glands (sudoriferous glands) </li></ul><ul><ul><li>Eccrine sweat glands </li></ul></ul><ul><ul><li>Apocrine sweat glands </li></ul></ul><ul><li>Tail Glands </li></ul><ul><li>Anal Sacs </li></ul>
    31. 31. Sebaceous Glands <ul><li>Located in the dermis; may be simple or complex alveolar structures </li></ul><ul><li>Most have a single duct that empties into hair follicle; others have ducts that empty directly onto surface of skin </li></ul><ul><li>Epithelial cells lining sebaceous gland manufacture and store sebum </li></ul><ul><li>Because the epithelial cell is lost in the process of secretion, the sebaceous gland is classified as a holocrine structure. </li></ul>
    32. 32. Sebaceous Glands <ul><li>Sebum </li></ul><ul><li>Composed primarily of glycerides and free fatty acids </li></ul><ul><li>Arrector pili muscle contracts and compresses sebaceous gland, forcing sebum through the duct into the hair follicle </li></ul><ul><li>Coats the base of the hair and surrounding skin </li></ul><ul><ul><li>Helps trap moisture, keeps hair soft, pliant, and somewhat waterproof </li></ul></ul><ul><ul><li>Sebum also helps reduce the skin's risk of infection. </li></ul></ul>
    33. 33. Sweat Glands <ul><li>Also called sudoriferous glands </li></ul><ul><li>Found over the entire body of most domestic species </li></ul><ul><li>Sweat helps cool the body through evaporation. </li></ul><ul><li>Two types of sweat glands: </li></ul><ul><ul><li>Eccrine </li></ul></ul><ul><ul><li>Apocrine </li></ul></ul>
    34. 34. Sweat Glands <ul><li>Eccrine Sweat Glands : </li></ul><ul><li>Excretory portion consists of a simple coiled tube located in the dermis or hypodermis </li></ul><ul><li>Empty onto surface of skin through a long duct </li></ul><ul><li>Apocrine Sweat Glands : </li></ul><ul><li>Coiled excretory portion buried in the dermis or hypodermis; single excretory duct </li></ul><ul><li>Empty into hair follicles </li></ul>
    35. 35. Tail Glands <ul><li>Oval region at the dorsal </li></ul><ul><li>base of the tails of most </li></ul><ul><li>dogs and cats </li></ul><ul><li>Contains coarse, oily hairs </li></ul><ul><li>Very large apocrine and </li></ul><ul><li>sebaceous glands present </li></ul><ul><li>Thought to assist with </li></ul><ul><li>recognition and identification </li></ul><ul><li>of individual animals </li></ul>
    36. 36. Anal Sacs <ul><li>Cats and dogs have anal sacs similar to musk glands of skunks. </li></ul><ul><li>Located at the 5 and 7 o'clock positions relative to the anus </li></ul><ul><li>Connected to the lateral margin of the anus by a small single duct </li></ul><ul><li>Lined with sebaceous and apocrine glands </li></ul><ul><li>When an animal defecates or becomes frightened, some or all of the anal sac contents are expressed. </li></ul>
    37. 37. Claws and Dewclaws <ul><li>Claws </li></ul><ul><li>Hard outer coverings of the distal digits </li></ul><ul><li>Usually pigmented </li></ul><ul><li>Function in maintaining traction and serve as tools for defense and catching prey </li></ul><ul><li>Claws are nonretractable except in most cat species </li></ul><ul><li>Dewclaws </li></ul><ul><li>Evolutionary remnants of digits </li></ul><ul><li>In the dog, the dewclaw is the first digit. </li></ul><ul><li>In the cow, pig, and sheep, the medial and lateral dewclaws are the second and fifth digits, respectively. </li></ul>
    38. 38. Hoof <ul><li>Horny outer covering of digits of some animals </li></ul><ul><li>Another name for “hoof” is ungula. </li></ul><ul><ul><li>Hoofed animals are called ungulates. </li></ul></ul><ul><li>Hooves rest on tissue called the corium. </li></ul><ul><li>The corium is attached to the periosteum of the distal phalanx. </li></ul><ul><li>The outer hoof is a modified epithelial layer, and the corium is modified dermis. </li></ul>
    39. 39. Hoof <ul><li>The skeletal foot of the horse includes the distal part of the second phalanx, the distal sesamoid bone (navicular bone), and the entire third phalanx (coffin bone). </li></ul><ul><li>The coffin bone has a layer of corium, which in turn is covered by the cornified hoof. </li></ul><ul><li>The hoof and the corium form interdigitations called laminae . </li></ul><ul><li>The equine hoof is generally divided into three parts: the wall, the sole, and the frog. </li></ul>
    40. 40. Hoof <ul><li>The wall : </li></ul><ul><li>External portion of the hoof visible from the anterior, lateral, and medial views; divided into the toe, the quarters, and the heels </li></ul><ul><li>The sole : </li></ul><ul><li>Plantar, or palmar, surface of the hoof; outer layers are avascular and lack innervation </li></ul><ul><li>The frog : </li></ul><ul><li>Triangular horny structure located between the heels on the underside of the hoof </li></ul><ul><li>Divided by a central depression known as the central sulcus </li></ul><ul><li>Digital cushion: a thick pad of fat and fibrous tissue lies beneath the sensitive frog </li></ul><ul><li>Lateral cartilages extend proximally from the distal phalanx </li></ul>
    41. 41. Horns <ul><li>Epidermal in origin </li></ul><ul><li>Structurally similar to hair </li></ul><ul><li>Composed of keratin </li></ul><ul><li>In adults the horn is hollow and communicates directly with the frontal sinus. </li></ul><ul><li>The corium lies at the root of the horn and is bound to the horn process by periosteum. </li></ul><ul><li>The body of the horn is composed of tightly packed tubules. </li></ul><ul><li>The wall of the horn is thinner at the base than at the apex. </li></ul>