Integumentary System

Anal sac

Paired sacs at 5 and 7 o'clock positions beside the anus that store scent secretions. These specialized glands produce distinctive odors used for territorial marking and individual identification in many mammals.

Anagen phase

The active growth phase of hair where cells rapidly divide and hair actively grows. During this phase, the hair follicle is fully developed and producing new hair shaft material continuously.

Apocrine sweat gland

Sweat glands that empty into hair follicles rather than directly onto the skin surface. These glands produce a thicker, more odorous secretion containing proteins and lipids.

Arrector pili muscle

Smooth muscle attached to hair follicles that contracts to make hair stand upright. These tiny muscles are controlled by the sympathetic nervous system and respond to cold, fear, or excitement.

Catagen phase

The transition phase when hair growth stops and the follicle begins to shrink. This brief phase occurs between active growth and the resting phase of the hair cycle.

Coffin bone

The distal phalanx inside the hoof, also called the third phalanx. This triangular bone provides structural support within the hoof capsule and bears the animal's weight.

Compound follicle

A follicle group where multiple hairs emerge from one opening in the skin. This arrangement is normal in many mammals and allows for dense hair coverage.

Corium

Sensitive tissue beneath the hoof or claw that's essentially modified dermis. This vascular tissue contains blood vessels and nerve endings that nourish the overlying horn structures.

Coronary band

The junction where the hoof wall meets the skin at the top of the hoof. This area contains the germinal tissue responsible for hoof wall growth.

Cortex

The thick middle layer of the hair shaft made of hard keratin. This layer provides the hair's strength, elasticity, and contains the pigment that gives hair its color.

Cuticle

The outermost single layer of hair cells arranged like overlapping roof shingles. This protective layer helps prevent moisture loss and protects the inner hair shaft.

Dermal papillae

Upward projections of dermis that interlock with the epidermis like puzzle pieces. These finger-like projections increase the surface area between skin layers and contain blood vessels.

Dermis

The thick, leathery layer of dense connective tissue beneath the epidermis. This layer contains blood vessels, nerve endings, hair follicles, and glands that support skin function.

Dewclaw

Rudimentary digit on the side of the leg that's essentially a vestigial toe. These claws don't typically bear weight and may be present on front legs, back legs, or both depending on the breed.

Eccrine gland

Sweat glands that open directly onto the skin surface and produce watery sweat for cooling. These glands are similar to human sweat glands but have limited distribution in most animals.

Epidermis

The outermost layer of skin made of keratinized stratified squamous epithelium. This avascular layer provides the primary barrier against water loss, infection, and environmental damage.

Frog

Triangular, rubbery structure on the bottom of a horse's hoof. This elastic tissue acts as a shock absorber and helps pump blood back up the leg with each step.

Hair bulb

The deepest, expanded part of the hair follicle where active hair growth occurs. This structure contains rapidly dividing cells that produce the hair shaft.

Hair follicle

The invagination of epidermis that anchors and produces hair. This complex structure includes the hair shaft, sebaceous glands, and arrector pili muscle.

Hoof wall

The visible outer covering of the hoof made of keratinized tissue. This hard structure protects the internal hoof structures and bears the animal's weight.

Horn

Permanent, keratinized growth from the skull in some ungulates. Unlike antlers, horns grow continuously throughout life and are never shed naturally.

Hypodermis

The fatty layer beneath the dermis that provides insulation and cushioning. This layer consists mainly of adipose tissue in loose connective tissue and allows skin mobility.

Integument

The skin and all its related structures including hair, glands, hooves, claws, and horns. This system forms the body's outer covering and first line of defense.

Keratinocyte

The main cell type in the epidermis that produces keratin protein. These cells start in the deepest layer and gradually move upward, filling with keratin as they mature.

Keratinization

The process where living skin cells fill with keratin protein, die, and become protective dead cells. This process creates the waterproof, protective outer layer of skin.

Laminae

Interdigitating layers that attach the hoof wall to the coffin bone like velcro. These sensitive tissues distribute weight and allow slight movement within the hoof.

Laminitis

Inflammation of the sensitive laminae in the hoof, commonly called "founder." This painful condition can cause rotation or sinking of the coffin bone within the hoof capsule.

Langerhans cell

Immune cells in the epidermis that detect and fight invading microorganisms. These specialized cells act as sentinels, capturing antigens and initiating immune responses.

Lanolin

Waxy substance from sheep sebaceous glands that waterproofs wool. This natural grease is secreted onto the wool fibers and has commercial uses in cosmetics and medications.

Matrix

Rapidly dividing cells in the hair bulb that form new hair. This germinal tissue is responsible for producing all the cells that make up the hair shaft.

Medulla

The innermost core of the hair shaft that may contain air spaces. This layer is not present in all hair types and provides additional insulation properties.

Melanin

Dark pigment that gives color to skin and hair while protecting against UV damage. This pigment is produced by melanocytes and transferred to surrounding cells.

Melanocyte

Cell that produces melanin pigment in the deepest epidermal layer. These star-shaped cells transfer pigment to surrounding keratinocytes to provide color and UV protection.

Merkel cell

Sensory cells at the epidermis-dermis junction that detect light touch and pressure. These specialized cells work with nerve endings to provide tactile sensation.

Papillary layer

The thin, superficial layer of dermis with loose connective tissue. This layer contains the blood vessels that nourish the overlying epidermis.

Phalanx bone

The small bone that forms one segment of a digit (toe or finger). In animals, each digit contains multiple phalanges arranged in a series.

Pigmentation

Coloration of skin, hair, or tissues caused by melanin deposits. The amount and distribution of pigment determines the animal's color patterns.

Planum nasale

The top of the nose in dogs, cats, pigs, and sheep. This specialized area of skin has unique texture and pigmentation patterns.

Polled breed

Breeds genetically lacking horns due to selective breeding. These animals never develop horns naturally and don't require dehorning procedures.

Primary hair

Long, thick guard hairs that are dominant in compound follicles. These coarser hairs form the outer coat layer and provide primary protection.

Pruritus

Medical term for itchiness or the sensation that provokes scratching. This symptom can indicate allergies, parasites, infections, or other skin conditions.

Reticular layer

The thick, deep layer of dermis with dense connective tissue arranged in a net-like pattern. This layer provides most of the skin's strength and elasticity.

Root

The part of hair buried within the skin below the surface. This portion includes the hair bulb and extends from the surface to the deepest part of the follicle.

Root hair plexus

Network of sensory nerves around the hair root that detects hair movement. These nerve endings make hair follicles extremely sensitive to touch.

Sebaceous gland

Oil glands in the dermis that produce sebum to lubricate skin and hair. These glands are usually associated with hair follicles and secrete their oily product into the follicle.

Sebum

Oily secretion that waterproofs and protects skin and hair. This lipid-rich substance prevents water loss and keeps skin supple.

Secondary hair

Soft, short, fine hairs that make up the undercoat. These wool-type hairs provide insulation and are more numerous than primary hairs.

Shaft

The visible part of hair above the skin surface. This portion extends from the skin surface to the hair tip and is composed of dead, keratinized cells.

Sinus hair

Tactile whiskers with large blood sinuses in the follicle that make them extremely sensitive. These specialized hairs are crucial for spatial awareness and navigation.

Sole

The bottom concave surface of the hoof that should not bear full weight. This area is softer than the hoof wall and provides some shock absorption.

Squamous cell carcinoma

Cancer arising from squamous epithelial cells in the skin. This malignant tumor often appears as irregular, ulcerated lesions that don't heal.

Stratum basale

The deepest epidermal layer where cells actively divide to replace the upper layers. This germinal layer sits on the basement membrane.

Stratum corneum

The outermost layer of dead, flattened keratin cells that provides the main protective barrier. This layer is constantly being shed and replaced.

Stratum germinativum

Alternative name for stratum basale, emphasizing its role in generating new cells. This layer contains stem cells that continuously divide.

Stratum granulosum

The middle layer where cells fill with granules and begin to die as part of the keratinization process. This layer helps create the skin's waterproof barrier.

Stratum lucidum

The clear layer found only in very thick skin like paw pads. This additional layer provides extra protection in high-wear areas.

Stratum spinosum

The "spiny layer" with multiple cell layers held together by strong connections. This layer provides strength and helps skin resist mechanical damage.

Subcutaneous layer

Alternative name for hypodermis, the fatty layer beneath the dermis. This layer provides insulation, cushioning, and energy storage.

Tail gland

Area rich in sebaceous and apocrine glands at the base of the tail in dogs and cats. This region produces distinctive scents for marking and communication.

Telogen effluvium

Massive hair loss when many hairs enter the resting phase together, commonly called "blowing the coat." This dramatic shedding is usually temporary.

Telogen phase

The resting phase when hair stops growing but stays in the follicle until it's pushed out by new growth. This phase can last weeks to months.

Ungula

Technical term for hoof, derived from Latin. This refers to the entire hoof structure including the wall, sole, and internal components.

Ungulate

Hoofed animal, referring to any mammal with hooves instead of claws or nails. This group includes horses, cattle, sheep, goats, and pigs.

White line

Junction between the hoof wall and sole that appears as a light-colored line. This area represents the connection between different types of horn tissue.