Glandular apparatus of the skin. Sebaceous and sweat glands

The glandular apparatus of the skin consists of the sebaceous and sweat glands of different structure and a diverse principle of functional activity.

The sebaceous glands (glandulae sebaceae) are related to holocrine glands in the character of secretion, i.e. glands in which the formation of the secretions is associated with physiological degeneration and decomposition of the cells of the gland. The intensively dividing epithelial cells of the sebaceous gland are arranged in a single row on the periphery of the sac of the gland. They are gradually displaced from the wall of the gland to the centre and undergo physiological degeneration as a result of which many drops of a fat-like substance form in them while the nuclei of the cells shrink. The cells that had undergone fatty degeneration swell and rupture, and the secretion of the gland, sebum, together with the cell fragments enters the wide draining duct of the gland.

The sebaceous glands are found in all skin areas with the exception of the skin of the palms and soles. In most cases they are connected to the hair follicles, one or more (up to six or eight) sebaceous glands surrounding a follicle. Contraction of the mm. arrectores pilorum promotes the discharge of the secretions. In the skin of the vermilion border, glans penis, inner surface of the prepuce, small pudendal lips, nipples, and the eyelid margins the sebaceous glands open directly on its surface without any association with the hair follicles, of which these areas are devoid. Sebaceous glands of the inner surface of the prepuce are called Tyson's glands (they produce smegma), those on the margins of the eyelids are known as maibomian glands. The amount of sebaceous glands not connected with the hair follicles varies greatly in man. The size of these glands is also just as variable; they are largest on the skin of the nose, cheeks, in the region of the sternum, and above and between the shoulder-blades.

The composition of the sebum is complex. It includes free and bound lower and higher fatty acids, cholesterol and isocholesterol esters, lipoids, protein products, phosphates, chlorides and other extractive substances.

The sweat glands (glandulae sudoriberae) are simple tubular glands which secrete sweat by reflex and play an important role in thermoregulation. In the human skin their number exceeds 3 million.

According to the character of secretion, eccrine and apocrine sweat glands are distinguished. In the process of secretion, the cells of the eccrine glands are preserved while the apical part of the cells of the apocrine glands is destroyed and turns into the secretions.

The sweat glands secrete 300 to 800 ml of sweat daily; in unfavourable conditions its amount reaches 1500 ml and more.

The eccrine sweat glands are found in all skin areas with the exception of the vermilion border, the glans penis, the inner surface of the prepuce, and the outer surface of the lesser pudendal lips. They are present in particularly large numbers in the skin of the palms, and soles and there are many of them on the forehead, chest, abdomen and forearms. The eccrine gland is a long epithelial tube which has a coiled end (the body of the gland) located in the deep layers of the dermis, less frequently in the upper layers of the hypoderm, and a long draining duct. The wall of the body, or the secretory part, of the gland consists of glandular cuboidal or columnar epithelium, a basement membrane, and a connective-tissue capsule. There is a layer of longitudinally stretching muscle fibres between the epithelium and the basement membrane. They are called the myoepithelial cells and contract under the effect of nerve impulses and thus contribute to the secretion of sweat.

The draining duct of the eccrine sweat gland stretched upward from the body of the gland almost perpendicular to the epidermis. In the dermis, the wall of the duct is formed of epithelial cuboidal cells, in the epidermis the duct has a twisted corkscrew shape and preserves its own walls.

The apocrine sweat glands are located predominantly in the axillae (where they form a whole layer 0. 5 to 4 mm thick) and there are very many of them around the anus, in the region of the nipples, the external female genitals, in the groin, on the pubis, and around the umbilicus. It was mentioned above that when these glands discharge their secretions part of the secretory cells die. The apocrine glands are larger than the eccrine glands, their draining ducts open into the hair follicles, while their body lies deep in the subcutaneous fat. The activity of the apocrine glands is linked with the activity of the sex glands and they therefore remain underdeveloped until the period of sexual maturation. In the elderly their function weakens.

The body (coil) of the sweat glands is surrounded by many capillaries forming a thick network. Innervation is mainly accomplished by branches of the sympathetic nerve, which are located in the connective-tissue capsule.