Glands of skin and there function

GLANDS OF SKIN

Skin contains two types of glands, namely sebaceous glands and sweat glands.

SEBACEOUS GLANDS

Sebaceous glands are

simple or branched alveolar glands, situated in the dermis of skin.

Structure

Sebaceous glands are ovoid or spherical in shape and are situated at the side of the hair follicle. These glands develop from hair follicles. So, the sebaceous glands are absent over the thick skin, which is devoid of hair follicles. Each gland is covered by a connective tissue capsule. The alveoli of the gland are lined by stratified epithelial cells. Sebaceous glands open into the neck of the hair follicle through a duct. In some areas like face, lips, nipple, glans penis and labia minora, the sebaceous glands open directly into the exterior.

Secretion of Sebaceous Gland – Sebum

Sebaceous glands secrete an oily substance called sebum. Sebum is formed by the liquefaction of the alveolar cells and poured out through the ducts either via the hair follicle or directly into the exterior.

Composition of Sebum

Sebum contains:

1. Free fatty acids

2. Triglycerides

3. Squalene

4. Sterols

5. Waxes

6. Paraffin.

Functions of Sebum

1. Free fatty acid content of the sebum has antibacterial and antifungal actions. Thus, it prevents the infection of skin by bacteria or fungi

2. Lipid nature of sebum keeps the skin smooth and oily. It protects the skin from unnecessary desquamation and injury caused by dryness

3. Lipids of the sebum prevent heat loss from the body. It is particularly useful in cold climate.

Activation of Sebaceous Glands at Puberty

Sebaceous glands are inactive till puberty. At the time of puberty, these glands are activated by sex hormones in both males and females.

At the time of puberty, particularly in males, due to the increased secretion of sex hormones, especially dehydroepiandrosterone, the sebaceous glands are stimulated suddenly. It leads to the development of acne on the face.

Acne

Acne is the localized inflammatory condition of the skin, characterized by pimples on face, chest and back. It occurs because of overactivity of sebaceous glands. Acne vulgaris is the common type of acne that is developed during adolescence. Acne disappears within few years, when the sebaceous glands become adapted to the sex hormones.

SWEAT GLANDS

Sweat glands are of two types:

1. Eccrine glands

2. Apocrine glands.

ECCRINE GLANDS

Distribution

Eccrine glands are distributed throughout the body. There are many eccrine glands over thick skin.

Structure

Eccrine sweat gland is a tubular coiled gland.

It consists of two parts:

1. A coiled portion lying deeper in dermis, which secretes the sweat

2. A duct portion, which passes through dermis and epidermis.

Eccrine sweat gland opens out through the sweat pore. The coiled portion is formed by single layer of columnar or cuboidal epithelial cells, which are secretory in nature. Epithelial cells are interposed bythe myoepithelial cells. Myoepithelial cells support the secretory epithelial cells. The duct of eccrine gland is formed by two layers of cuboidal epithelial cells.

Secretory Activity of Eccrine Glands

Eccrine glands function throughout the life since birth. These glands secrete a clear watery sweat. The secretion increases during increase in temperature and emotional conditions.

Eccrine glands play an important role in regulating the body temperature by secreting sweat. Sweat contains water, sodium chloride, urea and lactic acid.

Control of Eccrine Glands

Eccrine glands are under nervous control and are supplied by sympathetic postganglionic cholinergic nerve fibers, which secrete acetylcholine. Stimulation of these nerves causes secretion of sweat.

APOCRINE GLANDS

Distribution

Apocrine glands are situated only in certain areas of the body like axilla, pubis, areola and umbilicus.

Structure

Apocrine glands are also tubular coiled glands. The coiled portion lies in deep dermis. But, the duct opens into the hair follicle above the opening of sebaceous gland Apocrine sweat glands are nonfunctional till puberty and start functioning only at the time of puberty. In old age, the function of these glands gradually declines. The secretion of the apocrine glands is thick and milky. At the time of secretion, it is odorless. When microorganisms grow in this secretion, a characteristic odor develops in the regions where apocrine glands are present. Secretion increases only in emotional conditions.