the integument

skin and related structures such as hair, hooves, horns, claws, skin related glands

• epidermis
• dermis
• hypodermis

• cell types:
• keratinocytes - produce kerating, the tough fibrous, water proof protein that gives skin its resiliency and strength
• Melanocytes - produce the pigment melanin
• Merkel cells - phagocytize microinvaders; macrophage specific to epidermis
• Langerhans cells - found in the stratum spinosum; may be involved in allergic and cell mediated immune response to skin

• stratum germinatium or basale
• stratum spinosumer or spiny
• stratum granulosum or granular
• stratum lucidum or clear
• stratum corneum or horny

• basal layer
• deepest layer
• consists of a single row of keratinocytes attatched to the epithelial basement membrane
• Merkel cells, melanocytes and keratinocytes are found in this layer

• contains several layers of cells held together by desmosomes
• langerhans cells are found in this layer, where their slender projections form a weblike frame around the keratinocytes

• composed of 2-4 layers of flattened diamond shaped keratinocytes that contain lamallated granules of glycolipids
• these glycolipids play a role in helping to waterproof the skin and slowing water loss
• MIDDLE LAYER

• found in very thick skin
• composed of a few rows of flattened dead cells
• contents of the keratogranules combine with intracellular tonofilaments to form keratin fibrils

• composed of 20-30 rows of keratinocytes "remnants"
• sometimes called horny or cornified cells
• THE OUTER MOST LAYER
• DOMINATES THE EPIDERMIS

• hairy skin usually consists of 3 epidermal layers rather than 5
• stratum basale
• stratum spinosum
• stratum corneum
• the surface of hairy skin is covered in sale like folds
• a knoblike elevation can be seen periodically; tactile elevation or epidermal papilla, usually associated with a tactile hair

• composed of dense irregular conn tissue with collagen, elastic and reticular fibers
• also includes hair follicles, nerve endings, glands, smooth muscle, blood vessels and lymphatic channels
• fibroblasts, adipocytes and macrophages are also present

• Papillary Layer
• reticular layer

• underneath the epithelial layer of the epidermis
• composed of loose conn tissue with loosely woven fibers and ground substance
• dermal papillae help cement the epidermis and dermis together (little bumps that pop up)
• blood vessels, pain, temp, and touch receptors also present

• consists of dense irregular conn tissue
• bundles of collagen fibers from papillary layer blend into those of the reticular layer
• separations between bundles represent tension lines in the skin
• in areas where a great deal of bending occurs, dermal folds or flexure lines are present

• composed of areolar tissue containing adipose tissue, blood and lymphatic vessels and nerves
• contains special touch receptors called the pacinian corpuscle which is sensitive to heavier pressure than meissners corpuslce
• fibers of the hypodermis are continuous with those of the dermis
• hypodermal layer permits skin to move freely over underlying bone and muscle without putting tension on the skin

• pigmentation
• paw pads
• planum nasale
• ergots and chestnuts
• cutaneous pouches in sheep

• result of the presence or absence of melanin granules in the extensions of melanocytes
• no pigmentation if granules are concentrated around the nucleus of the melanocytes
• as granules move into the cellular extensions and into the surrounding tissue, pigmentation becomes macroscopically apparent
• the more granules present, the darker the pigmentation
• melanocyte - stimulating hormone controls dispersion of granules
• keratinocytes arrange melanin on the side of the cell with the greatest amount of sun exposure
• acts to protect keratinocytes from exposure to damaging ultraviolet rays

• thick layers of fat and connective tissue with exocrine sweat glands and lamallar corpuscles
• outer surface is the toughest and thickest skin in the body
• often pigmented; composed of all 5 epidermal layers
• conical papillae can be seen covering the entire pad

• top of the nose in cats, pigs, sheep and dogs
• planum nasolbiale - the muzzle of cows and horses
• usually pigmented
• aglandular except in sheep pigs and cows
• cpmposed of only 3 epidermal layers, germinativum, spinosum, corneum

• dark horny structures found on the legs of horses, ponies and other membranes of the equine family
• thought to be vestiges of carpal and tarsal pads of the 2nd and 4th digits (splint bones)

• infoldings in the skin
• infraorbital, interdigital and inguinal pouches
• contain fine hairs and numerous sebaceous and tail glands
• secrete a fatty yellow substance which covers and sticks to the skin when dry

• hair
• glands of the skin
• claws and dewclaws
• hoof
• horns

• hair strand and follicle
• types of hair
• functions of maintaining body temp; camouflage
• hair shaft is visible above the skin
• hair root is buried within the skin
• hair follicle anchors the hair
• deepest part of hair follicle expands to form a hair bulb
• at the base of the hair bulb is a mound of dermal cells called the papilla
• hair strands are formed as epithelial cells mature, fill with keratin and move away from papilla

• root sheath layers include the connective tissue root sheath, external root sheath and internal root sheath
• each hair strand is organized into three layers : cuticle, cortex and medulla

• anagen phase: cells are added at the base of the root , hair lengthens
• catagen phase: period of transiton between anagen and telogen phases
• telogen phase: maximum length of hair is achieved, hair stops growing, hair follicle shortens and hair is held in a resting phase

• melanocytes transfer melanin to the cortical and medullary cells that form the hair strand
• different colors result from the quantity and type of melanin incorporated into the hair
• *horses produce one type of melain*
• *dogs produce 2 types of melanin*
• as animals age, melanin production decreases and hair begins to turn grey
• white hair is formed when the cortex loses its pigment entirely and the medulla becomes completely filled with air

• Primary/guard hairs: straight or arched; thicker and longer than secondary hairs
• Secondary/wool hair: softer and shorter than primary hairs; wavy or bristled in the dog; predominant hair type is species with wool type coats
• Tactile/sinus hairs: contain numerous sensory ending, commonly known as whiskers; also mixed with intermittenly throughtout the hair coat, also called sinus hair cause of the large blood sinus located in the conn tissue portion of the follicel

• small, smooth muslce
• attatched to each hair follicle
• innervated by the sympathetic nervous system
• contraction of the muscle pulls the hair into an erect position

• Sebaceous glands
• Sweat glands (sudoriferous glands)
• Eccrine and Apocrine
• Tail Glands
• Anal Sacs

• Located in the dermis; may be simple or complex alveolar structures
• Most have a single duct that empties into the hair follicle; others have ducts that empty directly onto the suface of the skin
• Epithelial cells lining sebaceous gland manufacture and store sebum
• Because the epithelial cells is lost in the process of secretion, the sebaceous gland is classified as a Holocrine gland
• Composed primarily of glyceroids and free fatty acids
• Arrector pili muscles contrat and compresses sebaceous glands, forcing sebum through the duct into the hair follicle
• Coats the base of the hair and surrounding skin; helps trap moisture, keep hair soft, pliant and somewhat waterproof; sebum also helps reduce the skins risk of infection

• also called sudoriferous glands
• found over the entire body of most domestic species
• sweat helps cool the body through evaporation
• two types of sweat glands are Eccrine and Apocrine
• Eccrine Glands: found in the pads of animals; excretory portion consists of a simple coiled tube located in the dermis or hypodermis; empty into the surface of the skin through a long duct
• Apocrine Glands: coiled excretory portion buried in the dermis or hypodermis; single excretory duct; empty into the hair follicle

• an oval region at the dorsal base of the tails of most dogs and cats
• contains coarse, oily hairs
• very large apocrine and sebaceous glands present
• thought to assist with recognition and identification of individual animals

• cats and dogs have anal sacs similar to musk glands of skunks
• located at the 5 and 7 O'clock positon relative to the anus
• connected to the lateral margin of the anus by a small duct
• lines with sebaceous and apocrine glands
• when an animal defecates or becomes frightened, some or all of the material is expressed

• Claws: hard outer covering of the distal digits; usually pigmented; function in maintaining traction and serve as tools for defense and catching prey; claws are nonretractable except in most cat species.
• Dewclaws: evolutionary remnants of digits; in the dog, the dewclaw is the first digit; in the cow, pig and sheep, the medial and lateral dewclaws are the second and fifth digits, respectively

• horny outer covering of digits of some animals
• another name for hoof is ungula *hoofed animals are called ungulates*
• hooves rest on tissue called corium
• the corium is attatched to the periosteum of the distal phalanx
• the outer hoof is a modified epithelial layer and the corium is modified dermis
• 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)
• the coffin bone has a layer of corium,which in turn is covered by the cornified hoof
• the hoof and the corium from intergigitaitons called laminae
• the equine hoof is generally divided into three parts = wall, sole and frog

the external portion of the hoof visible from the anterior, lateral and medial views; divided into the toe, the quarters and the heels

plantar or palmar surface of the hoof; outer layers are avascular and lack innervation(nerves)

• triangular horny structure located between the heels on the underside of the hoof
• divided by a central depression known as the central sulcus
• digital cushion is a thick pasd of fat and fibrous tissue that lies beneath the sensitive from
• lateral cartilage extends proximally form the distal phalanx

• epidermal in origin
• structually similar to hair
• composed of keratin
• in adults, the horn is hollow and communicated directly with the frontal sinus
• the corium lies at the root of the horn and is bound to the horn process by periosteum
• the body of the horn is composed of tightly packed tubules
• the wall of the horn is thinner at the base than the apex