Integumentary System PDF

Integumentary System  General Functions of Integument Covers and protects underlying structures. Prevents desiccation (drying out). Assists in maintaining normal body temperature. Excretes water, salt, and organic wastes. Acts as a sensory organ, relaying tactile a...

Integumentary System  General Functions of Integument Covers and protects underlying structures. Prevents desiccation (drying out). Assists in maintaining normal body temperature. Excretes water, salt, and organic wastes. Acts as a sensory organ, relaying tactile and pressure information to the CNS. Involved in Vitamin D synthesis and nutrient storage. Structure of the Integument Composed of all four tissue types. Includes hair, horns, hooves, claws, and skin-related glands. Outer layer is composed of dead cells. Keratinization occurs as cells die, providing protective and regulatory functions.  Layers of the Skin 1. Epidermis ◦ Made of keratinized stratified squamous epithelium. 2. Dermis (Corium) ◦ Composed of dense fibroelastic connective tissue. 3. Hypodermis (Subcutaneous Layer/Subcutis) ◦ Primarily adipose tissue for thermal insulation and mechanical shock absorption. ◦ Contains pressure receptors known as Pacinian corpuscles, allowing skin to move freely over underlying muscle and bone ◦ Contains larger blood vessels and nerves.  Epidermis: Cells & Their Functions Keratinocytes ◦ Majority of epidermal cells. ◦ Produce keratin, a tough, fibrous, waterproof protein. ◦ Provides skin with resiliency and strength. Melanocytes Produce melanin, a dark brown-black pigment. Melanin is stored in membrane-bound granules called melanosomes. Melanin is absorbed by keratinocytes, providing protection from UV exposure. Langerhans Cells Macrophages found only in the epidermis. Originate in bone marrow and migrate to the skin. Function to phagocytize microbes and stimulate other immune cells.  Merkel Cells Form Merkel disks with sensory nerve endings at the epidermal-dermal junction. Thought to aid in touch sensation. Epidermal Layers (Deepest to Most Superficial) 1. Stratum Germinativum (Stratum Basale) ◦ Attached to the epithelial basement membrane. ◦ New cells are produced here and move up 2. Stratum Spinosum (Spiny Layer) ◦ Contains Langerhans cells. ◦ Cell death and keratinization begin here. 3. Stratum Granulosum (Granular Layer) ◦ Keratohyaline granules are synthesized here. 4. Stratum Lucidum (Clear Layer) ◦ Contains keratinized clear cells, found only in very thick skin. areas. 5. Stratum Corneum (Horny Layer) ◦ Outermost and thickest layer. ◦ Composed of cornified remnants of keratinocytes (dandruff).  ▪ Keratinization The process where keratinocytes produce keratin as they move up through the layers of the epidermis, eventually dying and forming a protective outer layer. As older cells move up from the basal layer, they fill with keratohyaline and glycolipid granules. Cells lose their nuclei, cytosol, and organelles, becoming dead sheets of keratin. Dead cells and keratin slough off as dander/dandruff. Dermis Makes up the largest part of the skin. Provides structural strength. Composed of two layers: ◦ Papillary Layer Loose connective tissue with fibers and ground substance. Located just beneath the epidermis; forms dermal papillae. ◦ Reticular Layer Dense irregular connective tissue containing collagen, elastic, and reticular fibers.  ▪ Comprises 80% of the dermis; most fiber bundles run parallel to one another. Orientation depends on the direction of stress placed on them. Special Features of Integument Foot/Paw Pads Characteristics: ◦ Thick layers of fat and connective tissue ◦ Tough, thick outer epidermal surface ◦ Often pigmented ◦ Composed of all 5 epidermal layers Functions: ◦ Bear the weight of the animal ◦ Protection against abrasion ◦ Protection against thermal extremes  ◦ Functional sweat glands that secrete onto the surface of the pad Planum Nasale Description: ◦ Top of the nose in dogs, cats, pigs, sheep, and goats ◦ Known as planum nasolabiale in horses and cattle ◦ Composed of only 3 epidermal layers in dogs ◦ Usually pigmented ◦ No glands in the epidermis or dermis in dogs ◦ Tubular glands present in ruminants and pigs Ergots and Chestnuts Ergots: ◦ Dark brown, horny patches on the legs of horses and other equids ◦ Vestiges of the 2nd and 4th digits Chestnuts: ◦ Vestiges of carpal and tarsal pads of the 1st digit  Cutaneous Pouches of Sheep Types: 1. Infraorbital 2. Interdigital 3. Inguinal Function: ◦ Infolding of skin forming pouches containing sebaceous (oil) glands ◦ Secretions used in marking territory, courtship, etc. Functions of Hair/Fur Thermoregulation: ◦ Insulates by trapping layers of air ◦ Hairs erect when cold Camouflage: ◦ Coat color determined by melanin and pheomelanin Communication: ◦ Intra- and interspecies communication ◦ Erection of hair when aroused or frightened ◦ Degree of erection indicates implantation angle  Arrector Pili Muscle Smooth muscle attached to hair follicle Innervated by the sympathetic nervous system Mixed intermittently throughout the coat Tactile hairs sensitive to touch and pressure, and help organisms sense their environment. They are found in many mammals, especially as whiskers Very sensitive to the slightest bending or touch  Hair Growth Cycles Anagen Phase Active growth phase Hair shaft lengthens Telogen Phase Quiescent, resting phase Occurs when maximum length is achieved Hair stops growing and follicle shortens Telogen Effluvium Loss of a large percentage of hair volume at one time Caused by metabolic stress or illness Catagen Phase Transitional period between anagen and telogen phases  Skin Glands Sebaceous Glands Located in the dermis (not in foot pads or nasal planum) Types: Simple or compound acinar gland Holocrine secretion Ducts: Empty into hair follicle Arrector pili muscle squeezes secretion out or empties directly onto the skin surface Secretion: Sebum (lanolin in sheep) Thick and oily Composed of glycerides and free fatty acids Coats hair and traps moisture Keeps skin moist and supple Has some antibacterial and antifungal properties Issues: Can clog follicles, causing whiteheads that turn black (comedones or blackheads) which can become infected  Sweat (Sudoriferous) Glands Present in most domestic species but only functional in equids and to a lesser extent in ruminants Types (both merocrine secretion): Eccrine Glands Empty onto skin surface Simple, coiled tube in dermis connected to skin surface by a long duct Found in foot pads and deep layers of fat in dogs Apocrine Glands Empty into hair follicles Single, coiled secretory/ excretory duct Located in the external ear canal Tail Glands Oily patch at the dorsal base of the tail in dogs and cats Contains sebaceous and apocrine glands Assists in communication and identification of individuals Sensitive to sex hormone levels  Anal Sacs Lined with sebaceous and apocrine glands Stores secretions produced Expressed during defecation or when the animal is frightened or excited Used in marking territory and attracting mates Claws, Hooves, Horns & Antlers Claws & Hooves Composition: Hard outer layer made of keratin. Inner layer called corium, which is a modified dermis. Functions: Provide traction for running, walking, and climbing. Assist in catching prey. Serve as a defense mechanism.  Horns & Antlers Horns: Origin: Epidermal (skin) origin, similar to hair. Structure: Generally hollow in adults and connect to the frontal sinus. Growth: Grow continuously and are not shed (except in pronghorn). Function: Used for defense, offense, and courtship. Breeding: Some domesticated animals are bred to be horn- free (polled), while others may be dehorned for easier handling. Antlers: Origin: Dermal bone that arises from the skull. Growth: Primarily found in males and are shed annually. Function: Also used for defense, offense, and courtship.  Ossicones Description: Conical or columnar structures made of skin-covered bone. Attached to the skull with vascularized, innervated connective tissue. Development: Start as cartilage, harden into bone, and fuse to the skull at sexual maturity. Presence: Found in both sexes of giraffes, but only in males of okapis.