Skin is the body’s largest organ, making up the body’s covering and about 15 percent of the total body weight The skin’s three layers-epidermis, dermis, and subcutaneous layer-help the body maintain its structure; protect against INFECTION; and regulate fluids, electrolytes, and temperature. Numerous health conditions, localized and systemic, can affect the skin and its functions.
The subcutaneous layer, innermost to the body, contains primarily adipose tissue more familiarly called body fat. The dermis, the middle layer, provides the structure of the skin. It contains connective tissue, the SEBACEOUS GLANDS, and an abundant supply of nerves and blood vessels. The dermis nourishes the epidermis above it and attaches to the subcutaneous layer beneath it, holding the skin in place. HAIR follicles and SWEAT GLANDS extend from the epidermis into the dermis and a bit into the subcutaneous layer.
The primary cells of the skin, melanocytes and keratinocytes, originate in the base, or basal, level of the epidermis. Keratinocytes migrate outward to form the upper epidermis, gradually flattening and hardening. The epidermis varies in thickness and other characteristics, accommodating the needs of different body surfaces. The epidermis of the palms of the hands and the soles of the feet is thick and tough, for example, while that of the eyelids is soft and only two or three cells in depth.
The skin is also the body’s organ of tactile sensory perception, or touch. Millions of NERVE endings in the skin continually sense environmental factors such as pressure, temperature, moisture. Other specialized nerve cells, called nociceptors, perceive itching and PAIN. Sweat evaporation on the skin’s surface is the body’s primary cooling mechanism, as well as a secondary mechanism for electrolyte regulation and balance.
|Health Conditions that may Affect the Skin|
|CRADLE CAP||DECUBITUS ULCER||DERMATITIS|
|DISCOID LUPUS ERYTHEMATOSUS (DLE)||EPIDERMOLYSIS BULLOSA||ERYSIPELAS|
|ERYTHEMA MULTIFORME||ERYTHEMA NODOSUM||FOLLICULITIS|
|KELOID||LICHEN PLANUS||LICHEN SIMPLEX CHRONICUS|
|TOXIC EPIDERMAL NECROLYSIS||URTICARIA||VITILIGO|
For further discussion of the skin within the context of integumentary structure and function, please see the overview section “The Integumentary System.”
See also KERATINOCYTE; MELANOCYTE; NAILS; SEBACEOUS GLAND.
Resource: Facts On File Encyclopedia Of Health And Medicine
Xanthoma is a fatty deposit that forms a benign (noncancerous) LESION beneath the SKIN, though also may occur in other tissues. Xanthomas develop in people who have chronic, untreated HYPERLIPIDEMIA (elevated BLOOD cholesterol and triglycerides levels). In their most common form, xanthomas appear as yellowish blebs beneath the skin, typically rounded or
Wrinkles are furrows or channels in the SKIN, typically resulting from repeated movements, such as facial expressions (for example, crow’s feet and laugh lines), or from long-term exposure to sun and wind. Aging is the single-most significant factor that causes wrinkles. Wrinkles increase with age as the skin loses collagen and subsequently
Whitlow is an INFECTION at the end of the finger, or less commonly the end of a toe, that contains pus and is very painful. The area is inflamed, enlarged, erythematous (reddened), and often oozing. A common cause of whitlow is infection with the HERPES SIMPLEX VIRUS (HSV), conveyed to the finger via contact with infectious secretions from oral herpes
Wheal is a raised, blisterlike LESION on the SKIN that usually results from an intradermal injection such as for ALLERGY skin testing or the tuberculin skin test. Wheals also may occur in response to insect stings and topical allergic reactions (URTICARIA or hives). Wheals associated with urticaria typically itch, sometimes intensely. Wheals usually do not
What are Warts and What Causes Warts Wart is a growth, typically rough and raised, that appears on the SKIN. The HUMAN PAPILLOMAVIRUS (HPV), which has numerous strains, causes common warts as well as variations including genital warts (a common sexually transmitted disease) and plantar warts which appear on the soles (plantar surfaces) of the feet. Because
Vitiligo - a condition of hypopigmentation in which melanocytes die in patches of SKIN, leaving macules that are pale and depigmented. Dermatologists believe vitiligo is an autoimmune disorder in which the IMMUNE SYSTEM produces antibodies that attack melanocytes, the skin cells responsible for producing pigment. Vitiligo affects people of all races and
Vesicle is a small, blisterlike LESION on the SKIN that contains serous fluid. Vesicles typically occur in clusters and indicate INFECTION, such as with HERPES SIMPLEX VIRUS (HSV), or irritation, such as results from contact with poison ivy. Skin vesicles often hurt or itch. Treatment may include topical medications to relieve discomfort, with oral
What is Urticaria and Definition Urticaria is the clinical term for hives, an outbreak of wheals on the SKIN’s surface. Acute urticaria, which comes on suddenly, typically signals a HYPERSENSITIVITY REACTION. The wheals contain fluid the IMMUNE RESPONSE draws from the cells of the skin. They itch, often intensely (PRURITUS), and may appear and recede
Toxic Epidermal Necrolysis is a life-threatening inflammatory condition affecting the SKIN and underlying connective tissues, also called Stevens-Johnson syndrome. Toxic epidermal necrolysis usually results as an adverse DRUG reaction though may occur as a complication of INFECTION or CANCER. Doctors believe toxic epidermal necrolysis develops when an
What is Tissue Expansion Tissue Expansion is a method for growing additional SKIN to use for autologous (self) skin grafts. Autologous grafts have the best rate of success when transplanted because they are native to the body and present no risk for graft rejection. Tissue expansion is a common method for many reconstructive surgery procedures, though