INTEGUMENTARY SYSTEM

Integumentary System

 “covering” Composed of:

•        Cutaneous membrane:

–       Epidermis - superficial epithelium

–       Dermis - underlying “cutaneous tissue” with blood supply

•         Accessory structures:

–       Hair

–       Nails

–       Exocrine glands

Functions:

•        Protect underlying tissues from infection, exposure and dehydration.

•         Excrete salts, water, and organic waste.

•         Maintain normal body temp (conserve and radiate heat).

•         Synthesize Vitamin D3 for calcium metabolism.

•         Store nutrients (fat).

•         Sensory detection: touch, pressure, pain, and temp.

Epidermis:

•        The corrugated border between dermis and epidermis helps bond epidermis to the dermis (increased surface area for attachment):

–       In thick skin, epidermal ridges show on the surface as fingerprints: function to enhance gripping.

•        Epidermis water resistant but not waterproof:

–       Insensible perspiration: water loss through epidermis: ~500ml (1 pint)/day (more if damaged, e.g. burn).

–        Callus: thickening of the epidermis, due to repeat friction

–       Blister: separation of epidermal layers of epidermis from dermis, space fills with interstitial fluid.

Skin color:

•        Pigment-based: epidermal pigments and blood pigments contribute to the color.

•        Epidermal Pigmentation:

–        Carotene: yellow-orange, from diet.

–        Melanin: brown, from melanocytes.

Sensory perception in integument:

•        Skin highly innervated for sensory perception, mostly in the dermis:

•         Tactile discs/Merkel cells:

–       deep layers of epidermis, superficial touch.

•         Free nerve endings:

–       the superficial dermis, pain, and temperature.

•         Tactile/Meissner’s corpuscles:

–       the superficial dermis, light touch.

•         Lamellated/Pacinian:

–       corpuscles -deep dermis, pressure and vibration.

Accessory Structures of the Integument:

•        Hair follicles and hair

•         Sebaceous glands

•         Sweat glands

•         Nails

v   All these structures are anchored in the dermis but are derived from epidermal tissue.

Hair Functions:

•        Head:

–        UV protection

–        Cushion from trauma

–        Insulation Nostrils, Ears canals, Eyelashes: -prevent the entry of foreign material.

•         Body hair:

–       Sensory detection

Integumentary Glands:

v  All are exocrine glands (secrete product onto skin surface via a duct).

•        Sebaceous glands:

–       Holocrine secretion

–        Secrete sebum into hair follicle 

Sebum: lipids +cholesterol + proteins + electrolytes.

•         Function:

–       lubricate and protect keratin.

–       Prevent evaporation.

–       Inhibit bacterial growth.

v   Sebaceous glands active in the fetus, then off until puberty, on whole adult life.

Sudoriferous glands / Sweat glands:

Merocrine/Eccrine sudoriferous glands:

•         Produce sensible perspiration: 99% water + electrolytes + organic nutrients + antibodies + antimicrobial agents + organic wastes.

–       Functions:

• Evaporative cooling of the surface of the skin to reduce body temp
• Excrete waste electrolytes and drugs
• Protection:

•  Prevent adherence of microbes (antibodies).
•  Physically wash off microbes.
•  Antimicrobial agents to kill microbes dermcidin (antibiotic).

•  Merocrine secretion.
•  Small coiled tubular glands.
•  Located in the superficial dermis.
•  Open directly on the surface of the skin.
• Secrete in response to high temp or stress.

•        Merocrine secretion

•         Armpits, nipples, groin

•         Secrete into the hair follicle

•         Secretion is sticky and cloudy:

–       sensible perspiration + proteins + lipids

•         Microbes eat it → wastes: body odor

•         Glands deep in the dermis

•         Surrounded by myoepithelial cells: a contract in response to sympathetic nervous system stimulation

•         Active only after puberty

•        Special apocrine sweat glands:

–        Mammary glands:

§  located in female breast -secrete milk during lactation.

–       Ceruminous glands:

§  located in external ear canal-secrete cerumen.

Nails:

•        Scale like projections on the dorsal surface of distal digits.

•         Functions:

–       Protect tips from mechanical stress, assist gripping.

–       Consists of dead cells containing hard keratin.

–       New nail formed at nail root -nail growth is continuous.

Injury and Repair:

•        Integument can function independently of nervous and endocrine systems to maintain own homeostasis.

•         Mesenchymal cells of the dermis can regenerate connective tissue.

•         Germinative cells (basal cells) of the epidermis can regenerate epithelial tissue.