Integumentary System PDF

Integumentary System Dr. Jacqueline Mobley AHS 2202 Introduction Integument = skin and associated structures Skin Claws Hooves Horns Hair Glands The integuments is one of the largest organs in the body Covers and protect un...

Integumentary System Dr. Jacqueline Mobley AHS 2202 Introduction Integument = skin and associated structures Skin Claws Hooves Horns Hair Glands The integuments is one of the largest organs in the body Covers and protect underlying structures within the body Keratinized  Integument Role of the integument Prevent desiccation Prevent infection Maintain body temperature Excretion of water, salt & organic wastes Receives sensory information Synthesis of vitamin D and storage of nutrients Skin thickness Thinnest – eyes & scrotum Thickest – center of the back, between shoulder blades, paw pads  Integument Histology 2 layers Epidermis Dermis (aka the corium) Separated by basement membrane Some species have a wavy basement mb forming “dermal papillae” Dermal papillae make skin stronger Epidermis Keratinized stratified squamous epithelium Waterproof shield Avascular Histology continued Dermis Fibroelastic connective tissue Makes up the majority of the integument Vascularized Hypodermis/Subcutaneous Primarily adipose tissue Shock absorber & insulation Epidermis Cells of the epidermis Keratinocytes – majority of epidermal cells, produce keratin Located along the basement mb Keratinization: Keratinocytes grow & divide, daughter cells push older cells up Older keratinocytes fill with keratohyalin granules and lose organelles Most superficial cells can exfoliate with no damage to the animal New epidermis forms every 7-8 weeks in humans  Cells of the epidermis Melanocytes – produce pigment melanin Long cellular projections (like an octopus) Melanin is stored in membrane bound granules called melanosomes Melanosomes are released into the keratinocyte Langerhans cells Macrophage in the epidermis Merkel cells Located at the epidermal-dermal junction Merkel disc: formed when Merkel cells touch a sensory nerve ending This Photo by Unkno wn Author is licensed under CC BY-SA-NC Aids in sensation of touch Layers of the epidermis - deep to superficial Stratum germinativum (Stratum basale) Formed by single layer of keratinocytes attached to basement membrane Also composed of Merkel cells & melanocytes Stratum spinosum Looks spikey histologically, but in live tissue is smooth Formed of several layers of keratinocyte cells held together by desmosomes Langerhans cells reside in this layer as well Stratum granulosum Formed of 2-4 layers of flattened, diamond-shaped keratinocytes Cells begin to fill with keratohyaline & lamellated granules (waterproofing) Layers of the epidermis continued Stratum lucidum (clear layer) Found in only VERY thick skin Forms a translucent layer of flattened dead cells Most skin does not have stratum lucidum Stratum corneum (horny layer) Outermost layer and dominates the epidermis (3/4 total thickness) Formed of 20-30 rows of keratinocytes Essentially these cells form “dandruff”  Dermis Majority of the integument Highly fibrous Dense, irregular connective tissue with collagen, elastic & reticular fibers Structures that live in the dermis Hair follicles Nerve endings Glands Smooth muscle Blood vessels Lymphatic channels Layers of the Dermis Papillary layer – thin, superficial Loose connective tissue Dermal papillae: Nipple-like projections, cement epidermis to dermis Looping blood vessels Meissner’s corpuscles – nerve endings (pain, touch) Temperature-sensing nerve endings Reticular layer – thick, deep layer, 80% of dermis Dense, irregular connective tissue Composed of parallel fibrous bundles “Tension lines” arise from separations in bundles Hypodermis or Subcutaneous Layer Thick layer, resides below the dermis Loose areolar tissue Adipose cells Blood & lymphatics Nerves Pacinian corpuscle: touch receptor sensitive to heavy pressure This Photo by Unkno wn Author is licensed under CC BY-SA-NC Special Features of the Integument Pigmentation Pigmentation arises from melanin granules produced by melanocytes More granules = more pigmentation/darker skin Melanocyte-stimulating hormone (MSH) controls dispersion of granules MSH is produced by the hypophysis in the brain Melanin protects the keratinocytes from exposure to UV rays Melanin is the sun hat for keratinocytes Paw Pads Thick padding Fat – insulating, shock absorbing, protective Outer layer of the pad is the toughest and thickest skin of the body Pigmented (usually) Contains all 5 epidermal layers Stratum corneum is thicker than all other 4 layers combined Microscopic conical papillae cover the pad Exocrine sweat glands & lamellar corpuscles present Planum Nasale Ergots & Chestnuts Dark, horny structures on the legs of equines Chestnuts Dark brown, inside of the leg at the carpus (knee) & tarsus (hock) Vestigial carpal & tarsal pads of 1st digit Ergots Small and less obvious than chestnuts, on the fetlocks Vestigial 2nd and 4th digits Cutaneous Pouches (Sheep) Cutaneous pouches = infoldings of the skin Fine hairs Sebaceous and oils glands Secrete fatty yellow substance that covers the skin Locations: Infraorbital pouches: In front of the eyes Interdigital pouches: Between the digits above the hooves Inguinal pouches: In the groin Related Structures of the Integument Hair Insulation Camouflage Most animals have fur (short, fine, falls out) as opposed to hair (long, keeps growing, needs to be cut) “Hair” Whales Pigs Humans Hair Strands and their follicles Shaft: the part above the skin Root: the part in the skin Hair follicle: anchors the hair in the dermis Hair bulb: deepest part of the follicle Papilla: mound of dermal cells at the base of the bulb Matrix: rapidly dividing epithelial cells covering the papilla Dividing cells are pushed upward, become keratinized, form hair Blood vessels supply the papilla Hair follicles continued Root hair plexus Sensory endings surround the root Provides important touch sensation when the hair is bent 3 layers to the hair follicle Internal epithelial root sheath Outer epithelial root sheath Dermal or connective tissue root sheath Hair follicles continued Compound follicles Multiple hair strands emerge from a single epidermal orifice (pore) Each strand of hair still has its own follicle and bulb Up to 15 strands of hair per pore Guard hair = long primary hair Satellite hairs = small secondary hairs surrounding guard hair Dogs typically have 3 compound follicles from one pore Hair Formation The hair structure: Formed of 3 concentric layers Core: medulla Cortex surrounds the medulla, hard keratin Cuticle: forms the hair surface Growth Cycles of Hair Shedding and growth occur constantly Environmental, hormonal and seasonal factors affect shedding Phases of hair cycle Anagen – hair growth Telogen - hair has reached maximal growth and is resting Catagen phase- period of transition between anagen and telogen Hair Color Horses have only one type of melanin Coat colors are based on the quantity of melanin Dogs have 2 types of melanin Pheomelanin – yellowish reddish colors Tyrosine melanin – brown black colors Agouti coloration – pigmentation accumulates at the tips  Types of Hair 3 types of hair Primary/guard hairs Straight, arched thick Secondary/wool-type hairs Softer, and shorter than primary hairs Tactile/sinus hairs Probers or feelers AKA whiskers This Photo by Unkno wn Author is licensed under CC BY-SA Arrector Pili Muscles Keep the hair erect Hair will stand up when frightened or cold Innervated by the sympathetic nervous system (fight or flight) Results in goosebumps in humans Forces sebum from the sebaceous gland to keep the skin moist & supple Glands of the Skin Sebaceous Glands Sebaceous glands 1) Single duct that empties into follicle 2) Ducts that empty straight onto the skin surface Sheep cutaneous pouches→ lanolin Holocrine gland (cell ruptures) Sebum – mixture of glycerides & FFAs Keeps skin lubricated, traps moisture Antibacterial & antifungal Arrector pili contracts and compresses gland to secrete sebum Sweat Glands “Sudoriferous glands” Present in most domestic species Only the horse makes profuse sweat This Photo by Unkno wn Author is licensed under CC BY Eccrine Sweat Glands Excretory portion: Simple coiled tube located in the dermis or hypodermis Empties onto the skin surface via a long duct Dogs: deep layer of fat and in foot pad connective tissue Apocrine Sweat Glands Excretory portion: coiled tube in dermis or hypodermis Empties into hair follicles Dogs: located in the external ear canal Tail Glands The tail gland Found in most cats and dogs Oval region at the dorsal base of the tail Can be seen visually as region of coarse, oily hairs Apocrine & sebaceous glands located here Believed to assist animals in recognizing each other Anal Sacs Located at 5 and 7 o’clock relative to the anus in cats & dogs Produces foul smelling glandular fluid Anal sacs are expressed when animal is afraid or defecates Assists in marking territory Claws and Dewclaws Claws: the hard pigmented covering of the distal digits Function: Traction and protection Cats are the only animals that retract their claws Except cheetahs Dewclaws: vestigial digits Sometimes contain bones The Hoof Hoof = “ungula” Hoof covers the coffin bone The wall, sole and frog make up the hoof Equivalent to the epidermis Hoof grows from the coronary band The Corium = sensitive tissue attached to the periosteum of the coffin bone Equivalent to the dermis Laminae: Interdigitations between the corium layer and the hoof, provides stability to keep hoof attached to bone The wall of the hoof The wall: the convex external portion of the hoof The toe (front) The quarters (lateral aspects) The heel (the back) https://www.epauk.org/about-equine-podiatry/articles/hoof-anatomy-a-beginners- guide/ The sole of the hoof The sole = the plantar surface of the hoof The corium connects the sole to the underside of the coffin bone The “white line” is the formed at the junction of the sole and the hoof wall https://www.epauk.org/about-equine-podiatry/articles/hoof-anatomy-a-beginners-guide/ The frog of the hoof The frog: triangular horny structure located between the heels on the underside of the hoof This Photo by Unknown Author is licensed under CC BY-NC-ND The leather-like frog provides shock absorption and supports the structures of the foot Apex of the frog faces the toe Central sulcus or cleft is the depression The 5 types of the corium Laminar corium: primary and secondary lamina, located between the hoof wall and the 3rd phalynx Laminitis in horses involves this section Perioplic corium: located in the perioplic sulcus Coronary corium: located in the coronary sulcus Sole corium: located superior to the sole Frog corium: located superior to the frog Horns Horns emerge from horn processes of the frontal bones Mass of horny keratin Usually hollow Corium is at the root and is bound to the horn process periosteum The wall at the base is thinner than the wall at the apex of the horn Most animals do not shed their horns Polled breeds are breeds bred to be horn free Antlers Usually on males Dermal in origin Arise as bone protuberances from the skull Shed annually Lack a central core and internal blood supply Nourished externally by soft, velvetlike tissue After completing growth, a dense ring of connective tissue forms at the base of the antler, strangling the velvet skin blood supply, resulting in hardening of the antlers Eventually the bony connection between the antler and skull breaks down, and the antler falls off The End This Photo by Unkno wn Author is licensed under CC BY-SA