sebaceous gland(redirected from Pilosebaceous unit)
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sebaceous gland(səbā`shəs), gland in the skinskin,
the flexible tissue (integument) enclosing the body of vertebrate animals. In humans and other mammals, the skin operates a complex organ of numerous structures (sometimes called the integumentary system) serving vital protective and metabolic functions.
..... Click the link for more information. of mammals that secretes an oily substance called sebum. In humans, sebaceous glands are primarily found in association with hairhair,
slender threadlike outgrowth from the skin of mammals. In some animals hair grows in dense profusion and is called fur or wool. Although all mammals show some indication of hair formation, dense hair is more common among species located in colder climates and has the
..... Click the link for more information. follicles but also occur in hairless areas of the skin, except for the palms of the hand and soles of the feet. Sebum is a mixture of fat and the debris of dead fat-producing cells. These cells are constantly replaced by new growth at the base of the glands. Generally the sebum is deposited on the hairs inside the follicles and is brought up to the surface of the skin along the hair shaft. In hairless areas, the sebum surfaces through ducts. Sebum lubricates and protects the hair and skin and prevents drying and irritation of membranes. Sebum may collect excessively as a result of poor hygiene, a diet rich in fats, or accelerated glandular activity, especially during adolescence. Excessive secretions of sebum may be related to acneacne,
common inflammatory disease of the hair follicles and sebaceous glands characterized by blackheads, whiteheads, pustules, nodules and, in the more severe forms, by cysts and scarring. The lesions appear on the face, neck, back, chest, and arms.
..... Click the link for more information. , certain forms of baldnessbaldness,
thinning or loss of hair as a result of illness, functional disorder, or hereditary disposition; also known as alopecia. Male pattern baldness, a genetic trait, is the most common cause of baldness among white males.
..... Click the link for more information. , and other skin disorders.
in humans and other mammals, a simple acinous gland with a short excretory duct and a branched end section that is located in the skin between the papillary and reticular layers of the dermis and that secretes cutaneus sebum. Sebaceous glands are distributed over the entire skin, except over the palmar and plantar surfaces.
Generally, sebaceous glands are connected to hairs: the excretory duct opens into the narrow fissure between the root and epithelial sheath of a hair. However, some glands, for example those on the lips, labia minora pudendi, nipples and nipple areas, and head and foreskin of the penis, open directly onto the body surface. The excretory duct is lined with stratified squamous epithelium, which on one side directly becomes the malpighian layer of the hair’s external root sheath and on the other becomes the wall of the alveolus. The latter consists of cells that are only slightly differentiated and capable of mitosis. These cells are rich in RNA and various enzymes and are especially concentrated near the excretory duct. The alveolus is filled with cells that contain fat droplets. Deep in the alveolus, cells undergo fatty degeneration, and as a result, their fat content increases and their nucleus wrinkles and decomposes.
Cutaneus sebum is formed from the remains of destroyed cells and fat. It serves as a fatty lubricant for the hair and skin surface and makes the skin elastic and impermeable to water, chemical substances, and certain microorganisms. The secretion of cutaneous sebum is promoted by the contraction of the skin musculature. The musk glands of certain reptiles and mammals and the uropygial glands of birds are sebaceous glands. In humans, the most common diseases of the sebaceous glands are atheroma, acne, and seborrhea.
E. S. KIRPICHNIKOVA