The sebaceous gland (lat. Glandula sebacea ) is a holocrine gland , in the upper part of the dermis located (dermis) lipids produced which, as tallow , sebum or sebum referred to reach the skin surface.
Most of the sebum glands are located in the skin of the field, distributed over the body surface, in the epithelium associated with a hair system and are therefore also called hair follicle glands . The remaining, so-called free sebum glands are located in certain skin regions such as lips, nostrils, ear openings, eyelids, nipples, genitals and anus.
The secreted sebum (lat. Sebum ) makes the hair and the top layer of the skin , the horny layer ( stratum corneum ), water-repellent, supple and shiny. It protects the skin, creates the physiologically acidic skin milieu, thus conditions the skin flora and thus enables the skin to be protected against pathogens. Hair and sebum are also combined into a functional unit, the hair sebum unit .
Special names are common for some free sebum glands: Zeis glands (after Eduard Zeis ) are small, individually standing sebum glands of the eyelid , Meibomian glands (after Heinrich Meibom ) are branched alveolar sebum glands (Glandulae sebaceae tarsales) in the edge area of the eyelids . Fordyce glands are free sebum glands in the oral mucosa and in the genital area, further free sebum glands in the area of the glans and clitoris are the Tyson glands .
The sebum is a holocrine gland and is located in the dermis . It belongs to the hair and sebum gland follicles and forms a lateral sac there. There are up to five glands per follicle. They have no exit of their own, but their secretion is directed along the hair to the skin. The exit is called the follicle exit. The sebum glands are not evenly distributed over the body:
- Regions with many sebum glands are the scalp , the genital area, the T-zone (on the face ) and the front and rear sweat troughs on the torso.
- Regions without sebum glands are the soles of the feet and palms.
Origin and function of sebum
Sebum is formed by sebocytes (sebum cells) within the cell (intracellularly) and released to the surface of the skin when the cells burst ( holocrine secretion ). It consists of triglycerides , fatty acids and wax esters .
The sebum wall has a similar structure to the stratum basale (basal cell layer ) of the epidermis . It also has a germ layer that keeps producing new sebocytes (cells that produce sebum). The newly created cells migrate to the center of the gland and begin to produce lipids (fats). These accumulate in the cells. By the time they get to the center of the gland, they have accumulated so much lipids that they will burst. The cells themselves become part of the sebum. If this sebum then tries to push its way through the follicle exit onto the skin, it tears off keratinized cells from the follicle wall when it is pushed up and takes them up to the skin. The horn leaflets come from the stratum corneum disconjunctum (→ epidermis ).
The amount of sebum produced depends on several factors:
- Hormones like dihydrotestosterone
- Nutritional status (when hungry, sebum production is reduced)
- Environmental influences
1–2 g of sebum form on the surface of the skin every day. The sebum prevents the skin from drying out. With age, sebum production decreases, making the skin drier and more vulnerable.
Composition of sebum
The composition of sebum varies from person to person. Guide values are:
- Triglycerides approx. 43%
- free fatty acids approx. 15%
- Wax approx. 23%
- Squalene approx. 15%
- Cholesterol approx. 4%
To this fat blend come proteins .
If the production is disturbed, skin diseases can develop. A distinction is made between seborrhoeic people with excessive sebum production and sebostatic people with low sebum production. A blockage of a sebum gland can lead to secretion congestion. A pore can develop into which pathogens can increasingly penetrate. This is how a blackhead can form. See also: acne
In veterinary medicine , idiopathic inflammations of the sebum glands occur occasionally in dogs and cats , which can lead to the irreversible loss of the sebum function. In these cases, one speaks of sebadenitis . It is probably a hereditary disease .
- Klaus Mörike among other things: Human biology . Quelle & Meyer, Wiebelsheim 2001, ISBN 3-494-01297-0 , p. 501.
- Sebaceous glands Dr Jastrow's EM Atlas
- Doctoral thesis on clinical and histological aspects of sebum nevus