Integument System: Skin, Feathers, and Reptile Skin Structures

Integument system

Largest and most extensive systems that covers and protects underlying structures, including skin and related skin structures.

Keratinization

Process by which keratin cells stratify and the top layer consists of dead skin cells.

Functions of the integument system

Covers and protects, prevents desiccation (dehydration), reduces threat of injury, maintenance of body temperature, excretes water, salt, organic wastes, receives and conveys sensory information, synthesizes vitamin D, and stores nutrients.

Epidermis

Outer waterproof shield of the skin, formed by stratified squamous epithelium.

Dermis

Majority of skin that provides structural strength, consisting of fibroelastic connective tissue.

Hypodermis

Subcutaneous layer made of adipose tissue that acts as a thermo-insulator and mechanical shock absorber.

Keratinocytes

Majority of cells in the epidermis that produce keratin protein, providing skin resiliency and strength.

Melanocytes

Cells responsible for melanin pigment production, found in deep epidermal layers.

Merkel cells

Cells found in small numbers at the epidermal-dermal junction, associated with sensory nerve endings to aid in the sensation of touch.

Langerhans cells

Macrophages specific to the epidermis that phagocytize micro-invaders and stimulate the immune system.

Papillary layer

Thin loose connective tissue in the dermis containing pain receptors and temperature regulation structures.

Reticular layer

Dense irregular connective tissue in the dermis that accounts for 80% of the dermis, providing strength, elasticity, and support.

Hair shaft

Part of hair visible above the skin.

Hair root

Part of the hair buried within the skin.

Hair bulb

Deepest part of the hair follicle.

Hair follicle

Pore that surrounds the root and shaft of the hair.

Medulla

Innermost layer of hair, made of soft keratin.

Cortex

Surrounds the medulla and is made of hard, rigid keratin; it is the thickest of the three hair layers.

Cuticle

Forms the hair surface, made of hard keratin with layered cells to prevent matting.

Primary hairs

Straight or arched, thick and long hairs that are dominant.

Secondary hairs

Softer and shorter than primary hairs, predominant in wool-type coats.

Tactile hairs

Sinus hairs that are sensitive to bending or touch, used as probes and feelers.

Pigmentation

Caused by the presence or absence of melanin, controlled by the hypophysis (pituitary gland) which secretes MSH (melanocyte stimulating hormone).

Paw pads

Thick layers of fat and connective tissue, toughest and thickest skin on the body, often pigmented and composed of all epidermal layers.

Planum nasale

The surface of the nose in certain animals, characterized by its unique structure.

Planum nasolabiale

Muzzle of cows and horses

Ergots

Smaller and often overlooked, buried in caudal hairs of fetlock, vestiges of second and fourth digits

Chestnuts

Dark brown rigid structure on medial side of leg at carpus and hock, vestiges of the first digits

Cutaneous pouches in sheep

Infoldings of skin found in sheep, in front of eyes, between digits, and groin, contain fine hairs, sebaceous, and oil glands, secrete a fatty yellow substance that coats skin

Arrector Pili Muscle

Small smooth muscle attached to the hair follicle, contractions pull hairs erect, controlled by sympathetic nervous system

Sweat glands

Sudoriferous glands that produce watery transparent liquid, cools body through evaporation

Accrine sweat glands

Empty onto skin surface

Apocrine sweat glands

Empty into hair follicles

Sebaceous glands

Located in dermis, most have a single duct that empties into hair follicle, others have ducts that empty directly onto skin, sebum is an oily lipid substance manufactured and stored by cells

Lanolin

Substance produced by sheep

Uropygial (Preen) Gland

Gland in birds that secretes oily fatty substance, waterproofs feathers, can vary in size with species, lacking in some species

Tail glands

Oval region at dorsal base of tail that assists with identification of individuals, recognizable by presence of coarse oily hairs

Anal sacs (Musk glands)

Glands with malodorous secretions, lined with sebaceous and apocrine glands, expressed via defecation or fright, located at 5 and 7 o'clock positions relative to the anus

Claws

Hard outer coverings of distal digits, tools for defense and catching prey

Dewclaws

Remnants of digits in dogs (1st digit), cows, pigs, and sheep (2nd and 5th digits)

Hooves

Found in ruminants (sheep, cattle, goats), four hooves per foot, only walk on two hooves (3rd and 4th), other two are dewclaws

Corium

Underlying sensitive tissue that claws and hooves rest on, outer layer is modified epithelial tissue, inner layer is modified dermis, well innervated and sensitive to pain, rich with blood vessels that provide nutrients to the hoof

Equine hoof

Grows from coronary band downward, growth is continuous, trimming maintenance required, consists of the wall, sole, and frog

Wall of hoof

External portion of the hoof, divided into toe, quarter, and heel

Sole of hoof

Planter or palmar surface of hoof, outer layers avascular and lack sensation, white line formed at sole and hoof wall

Frog of hoof

Insensitive triangular rigid structure with central sulcus (cleft), collateral sulci, base, and apex

Horns

Mass of horny keratin that grows continuously, not sex specific, structurally like hair, epidermal in origin, communicate with frontal sinus

Bird skin

Epidermis consists of thin flat epithelial cells that produce keratin, dermis is thick tough fibrous connective tissue, storage for fat, smooth muscle innervates feathers to regulate heat.

Hot temperature response in birds

Depressor muscles promote heat loss

Cold temperature response in birds

Erector muscles elevate feathers to trap warm air

Smooth muscle

Innervate feathers to regulate heat.

Hot

Depressor muscles promote heat loss.

Cold

Erector muscles elevate feathers to trap warm air.

Avian feathers

Necessary for flight, protects skin from trauma and environment, thermoregulation and camouflage, communication, courtship, defense, and recognition.

Feathers

Outgrowths of skin that are made of protein.

Feather tracts

Do not originate from entire body.

Pterylae

Feathers overlap each other; narrow tracts in the skin.

Apteria

Base areas of skin between tracts.

Vane

Flattened part of a feather on each side of the rachis.

Barbs

Numerous slender, closely spaced structures that give rise to barbules.

Barbules

Have rolled edges and hooklets known as hamuli.

Hamuli

Hooklets that interlock each barb, forming a tightly linked web.

Contour feathers

Typically cover the body; includes flight feathers of wing and tail.

Remiges

Flight feathers in the wing.

Rectrices

Tail feathers.

Semiplume feathers

Possess a main rachis with barbs, lacks barbules and hooklets, found under contour feathers, provides insulation and buoyancy in water birds.

Down feathers

Soft and fluffy, lack a shaft, barbules, and hooklets, primarily for insulation.

Filoplume feathers

Bare shaft with barbs only at the tip, contain nerve endings, aid in feather movement.

Bristles

Stiff rachis with few barbs at base, aid in sense of touch.

Powder down feathers

Grow continuously at the base, create a waxy powder, provides waterproofing of body.

Molting

Process of feather replacement that can occur several times a year.

Blood feathers

Growing feathers seen in the shaft during growth.

Beaks

Upper and lower mandible covered with tough keratin layers.

Epidermis (reptiles)

Scales varied in size and shape, form specialized structures like crests, tubercles, spines, dewlaps.

Dermis (reptiles)

Contains osteoderms providing protection and support, and chromophores responsible for color change.

Tortoise shell

Extension of rib cage, consists of plastron, carapace, and bridge, made up of numerous small bones covered by keratin scutes.

Ecdysis

Shedding of the skin, occurs in response to growth or injury, under the control of the thyroid gland.

Hypodermis "Subcutaneous"

Thick layer below the dermis, loose layer of areolar tissue, contains adipose and nerves.