In holocrine secretion, glandular cells themselves become a component of a secretion by perishing during secretion. Such a mechanism is present in the human organism in the secretion of sebum. Both overproduction and underproduction of sebum can be pathological.
What is holocrine secretion?
Holocrine secretion is found, for example, in human sebaceous glands. The secreting cells themselves become the secretion and completely disintegrate during secretion. Sebaceous glands here above the hair root, shown in yellow. Holocrine secretion is a secretion mode of exocrine secretory glands. In addition to holocrine secretion, the human organism has the modes of apocrine and eccrine secretion. Holocrine secretion is found, for example, in human sebaceous glands. Especially in the context of apoptosis, i.e. programmed cell death, the holocrine secretion mode of the sebaceous glands is readily associated. During holocrine secretion, the secreting cells themselves become secretions and completely disintegrate during secretion. They are replaced by regrowing glandular cells that advance toward the glandular lumen. This advancement of new cells removes the old glandular cells so far from the basement membrane that they can no longer be adequately nourished. As a consequence, they degenerate, lose contact with the surrounding cells and are rejected. Only the disintegrated membrane and the contents of the cells result in the greasy-looking and actual secretion.
Function and task
Using the example of the sebaceous glands, holocrine secretion can be understood in detail. Sebum is formed intracellularly by so-called sebaceous cells. Several sebaceous cells are located in the interior of each sebaceous gland. Only when the individual cells burst open does the sebum reach the surface of the skin. The sebaceous secretion thus contains triglycerides as well as wax esters and fatty acids. Each sebaceous gland wall resembles the epidermal basal cell layer. It is equipped with a germinal layer on which new sebum-producing cells are permanently formed. Thus, the epithelium is permanently regenerated from the basal cell layer. A part of the cells remains in the form of stem cells near the basal membrane. The other part is displaced by the descendant cells, loses contact with the membrane and migrates towards the lumen. The further the cells are displaced, the less diffusion-based nourishment can occur. The sebaceous cells move to the center of the gland as they migrate, producing lipids continuously. The lipids are collected and stored by the cell. Lipid droplets form on the surface and connect the migrating sebaceous cells. Once a sebaceous cell reaches the center of the gland, it gradually perishes due to the stored lipids and nutritional situation. Thus, a kind of sebaceous mush is formed from the fats together with the cellular components of the ruptured sebaceous cell. When this mush pushes out through the exit of the follicle onto the skin surface, the horny cells of the follicle wall are torn off and move out onto the skin together with the sebaceous mush. How much sebum is produced each day in this way is determined by predisposition and hormones. Age, nutritional status and various environmental influences can also affect sebum production. On average, daily production is one to two grams per day. Without the sebum or holocrine secretion, the skin surface would dry out. Holocrine secretion is formed in the human organism only by the sebaceous glands. The large branched alveolar sebaceous glands in humans are usually located on hair shafts. The small simple alveolar sebaceous glands are located on the skin. Meibohm’s glands are called the large branched and alveolar sebaceous glands on the eyelid and the small sebaceous glands on the eyelashes are also called Zeiss’s glands.
Diseases and disorders
The holocrine secretion of the sebaceous glands can be disturbed by various diseases. Usually, impaired sebaceous secretion is noticeable in the form of skin diseases or at least abnormalities on the skin. If there is excessive holocrine secretion, it is also called seborrhea. This phenomenon can be symptomatic in Parkinson’s disease, acromegaly or phenylketonuria and thyrotoxicosis. The skin becomes abnormally greasy. A special form of the phenomenon is the disturbed secretion due to a sebaceous gland closed by overproduction.In this phenomenon, a so-called sebum buildup occurs after a certain time. The pores of the skin widen and thus offer pathogens the best possible opportunities for entry. In addition, the sebaceous congestion promotes the formation of blackheads. This phenomenon occurs, for example, in the context of acne. A distinction must be made between this and reduced holocrine secretion, such as that suffered by sebostatic patients. Their skin becomes cracked and abnormally dry. Inflammation of the sebaceous glands can also have an effect on their ability to function and thus on holocrine secretion. Such inflammatory reactions are referred to as sebadenitis, which is rather rare in humans and can lead to irreversible damage to the holocrine glands. As an idiopathic disease, sebadenitis and its causes have not yet been conclusively investigated. A genetic cause is currently suspected. An equally rare phenomenon is sebaceous gland carcinoma. In this malignant cancer, the cells from which sebaceous glands should actually form degenerate. A common disease of the sebaceous glands on the eye is stye, also known as hordeolum. This condition is usually caused by bacteria and triggers a painful inflammation that manifests as redness and swelling of the eyelid.