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Vet130 A&P 1
Ch. 5 The integument and related structures
Veterinary Medicine
Undergraduate 1

Additional Veterinary Medicine Flashcards




Integumentary System
  • Skin and related structures:
    • Hair, hooves, horns, claws, skin-related glands
  • 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


Integumentary System Consists of what three layers?
  • Epidermis
  • Dermis
  • Hypodermis



Cell types:

Keratinocytesproduce keratin, the tough, fibrous, waterproof protein that gives skin its resiliency and strength 

Melanocytes produce melanin pigment

Merkel cellsphagocytize microinvaders; macrophage specific to epidermis 


Langerhans cellsfound in stratum spinosum; may be involved in allergic and cell-mediated immune response in skin 

Epidermal Layers
  • Stratum germinativum (basal layer): Deepest layer
  • Stratum spinosum (spiny layer)
  • Stratum granulosum (granular layer): Middle layer
  • Stratum lucidum (clear layer)
  • Stratum corneum (horny layer): Outermost layer


Stratum germinativum (basal layer)
  • Deepest layer
  • Consists of a single row of keratinocytes attached to epithelial basement membrane 
  • Merkel cells, melanocytes, keratinocytes, found in this layer


Stratum spinosum (spiny layer)
  • Contains several layers of cells held together by desmosomes 
  • Langerhans cells found in this layer


Stratum granulosum (granular layer)
  • Middle layer
  • Composed of two to four layers of flattened, diamond-shaped keratinocytes that contain lamellated granules of glycolipids 
  • Glycolipids play a role in helping waterproof the skin and slowing water loss across the epidermis


Stratum lucidum (clear 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


Stratum corneum (horny layer)
  • Composed of 20 to 30 rows of keratinocyte “remnants” 
  • Sometimes called horny or cornified cells
Epidermis of Hairy Skin
  • Hairy skin usually consists of three epidermal layers rather than five (stratum basale, stratum spinosum, and stratum corneum)
  • The surface of hairy skin is covered in scalelike folds
  • A knoblike elevation can be seen periodically
  • Tactile elevation or epidermal papillae
  • Usually associated with a tactile hair (tylotrich hairs)


  • Composed of dense irregular connective tissue 
    • Collagen, elastic, and reticular fibers 
  • Also includes hair follicles, nerve endings, glands, smooth muscle, blood vessels, and lymphatics 
  • Fibroblasts, adipocytes, and macrophages also present
  • Two layers: 
  1. Papillary layer 
  2. Reticular layer


Dermal Layers

Papillary layer 

  • Underneath the epithelial layer of the epidermis 
  • Composed of loose connective tissue with loosely woven fibers and ground substance 
  • Dermal papillae help cement the epidermis and the dermis together
  • Blood vessels, pain, temperature,  and touch receptors also present


Dermal Layers

Reticular layer 

  • Consists of dense irregular connective tissue
  • Bundles of collagen fibers from papillary layer blend into those of reticular layer 
  • Most fibrous bundles tend to run parallel to each another.
  • Separations between bundles represent tension lines in skin
  • In areas where a great deal of bending occurs, dermal folds or flexure lines are present.


  • Composed of areolar tissue containing adipose, blood and lymphatic vessels, and nerves 
  • Contains special touch receptor  – the pacinian corpuscle (sensitive to heavier pressure than Meissner's corpuscle) 
  • Fibers of hypodermis are continuous with those of dermis 
  • Hypodermal layer permits skin to move freely over underlying bone and muscle without putting tension on skin


Special Features of the Integument
  • Pigmentation
  • Paw Pads
  • Planum Nasale
  • Ergots and Chestnuts
  • Cutaneous Pouches in Sheep



  • Result of presence or absence of melanin granules in the extensions of melanocytes 
    • No pigmentation if granules are concentrated around nucleus of the melanocyte 
    • As granules move into the cellular extensions and into 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 greatest amount of sun exposure
  • Acts to protect keratinocytes from exposure to damaging ultraviolet rays


Paw Pads
  • Thick layers of fat and connective tissue with exocrine sweat glands and lamellar corpuscles
  • Outer surface is the toughest and thickest skin in the body 
  • Often pigmented; composed of all five epidermal layers
  • Stratum corneum is thicker than all other layers combined 


Conical papillae can be seen covering entire pad

Planum Nasale
  • Top of the nose in cats, pigs, sheep, and dogs
  • Planum nasolabiale: the muzzle of cows and horses
  • Usually pigmented; aglandular except in sheep, pigs, and cows
  • Composed of only three epidermal layers:
    • Stratum germinativum, stratum spinosum, stratum corneum  
    • Not present: stratum lucidum, stratum granulosum


Ergots and Chestnuts
  • Dark horny structures found on the legs of horses, ponies, and other members of the equine family 
  • Thought to be vestiges of carpal and tarsal pads of second and fourth digits ("splint bones")


Cutaneous Pouches in Sheep
  • Infoldings of skin 
  • Infraorbital, interdigital, and inguinal pouches 
  • Contain fine hairs and numerous sebaceous and oil glands 
  • Secrete a fatty yellow substance which covers and sticks to the skin when dry
Related Structures of the Integument
  • Hair
    • Hair strands and follicles
    • Types of hair
  • Glands of the skin
    • Sebaceous and sweat glands
    • Tail glands
    • Anal sacs
  • Claws and dewclaws
  • Hoof
  • Horns



  • Functions in maintaining body temperature; camouflage
  • Hair shaft: visible above the skin 
  • Hair root: 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 the papilla.


Hair Follicle
  • Root sheath layers: connective tissue root sheath, external root sheath, and internal root sheath 
  • Each hair strand is organized into three layers: cuticle, cortex, and medulla
  • Root hair plexus: web of sensory nerve endings 
    • Touch receptor


Growth Cycles of Hair
  • Anagen phase: cells are added at the base of the root, hair lengthens
  • Catagen phase: period of transition 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
Hair Color
  • 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 only one type of melanin; dogs produce two.
  • As animals age, melanin production decreases and hair begins to turn gray. 
  • White hair is formed when the cortex loses its pigment entirely and the medulla becomes completely filled with air.
Types of Hair

1.Primary or guard hairs

  • Straight or arched; thicker and longer than secondary hairs

2.Secondary or wool-type hairs

  • Softer and shorter than primary hairs; wavy or bristled in the dog; predominant hair type in species with wool-type coats

3.Tactile (or “sinus”) hairs 

  • Contain numerous sensory endings 
  • Commonly known as whiskers; also mixed intermittently throughout the hair coat 
  • Also called sinus hair because of the large blood sinus located in the connective tissue portion of the follicle


Arrector Pili Muscle
  • Small, smooth muscle 
  • Attached to each hair follicle 
  • Innervated by sympathetic nervous system
  • Contraction of the muscle pulls the hair to an erect position
Glands of the Skin
  • Sebaceous Glands
  • Sweat glands (sudoriferous glands)
    • Eccrine sweat glands 
    • Apocrine sweat glands
  • Tail Glands
  • Anal Sacs


Sebaceous Glands
  • Located in the dermis; may be simple or complex alveolar structures
  • Most have a single duct that empties into hair follicle; others have ducts that empty directly onto surface of skin
  • Epithelial cells lining sebaceous gland manufacture and store sebum
  • Because the epithelial cell is lost in the process of secretion, the sebaceous gland is classified as a holocrine structure.


  • Composed primarily of glycerides and free fatty acids
  • Arrector pili muscle contracts and compresses sebaceous gland, forcing sebum through the duct into the hair follicle
  • Coats the base of the hair and surrounding skin 
    • Helps trap moisture, keeps hair soft, pliant, and somewhat waterproof 
    • Sebum also helps reduce the skin's risk of infection.


Sweat Glands
  • 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: 
    • Eccrine 
      • Excretory portion consists of a simple coiled tube located in the dermis or hypodermis 
      • Empty onto surface of skin through a long duct
    • Apocrine
      • Coiled excretory portion buried in the dermis or hypodermis; single excretory duct 
      • Empty into hair follicles
Tail Glands
  • 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


Anal Sacs
  • Cats and dogs have anal sacs similar to musk glands of skunks.
  • Located at the 5 and 7 o'clock positions relative to the anus
  • Connected to the lateral margin of the anus by a small single duct 
  • Lined with sebaceous and apocrine glands 
  • When an animal defecates or becomes frightened, some or all of the anal sac contents are expressed. 


Claws and Dewclaws


  • Hard outer coverings 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


  • 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 the corium. 
  • The corium is attached 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 form interdigitations called laminae. 
  • The equine hoof is generally divided into three parts: the wall, the sole, and the frog. 


5 types of corium in the hoof
  • Laminar: primary and secondary lamina. Located between hoof wall and third phalanx. Provides nutrients to stratum internum
  • Perioplic corium: located in the coronary sulcus and supplies nutrients to periople
  • Coronary corium: found in the coronary sulcus and provides nutrients to the sole
  • Sole corium: superior to the sole and provides nutrients to the sole
  • Frog corium: superior to the frog and provides nutrients to the frog




Lamellae – interlocking of dermal and epidermal lamellae 


The wall:

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

The sole:

  • Plantar, or palmar, surface of the hoof; outer layers are avascular and lack innervation

The frog:

  • 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: a thick pad of fat and fibrous tissue lies beneath the sensitive frog
  • Lateral cartilages extend proximally from the distal phalanx 


  • Epidermal in origin 
  • Structurally similar to hair 
  • Composed of keratin 
  • In adults the horn is hollow and communicates 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 at the apex.


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