In apocytosis, the membrane of a glandular cell is sequestered along with the secretion in containers. This is a secretory mode of apocrine glands that is a special form of exocytosis and primarily affects the mammary gland. Disorders of hormonal balance may alter apocytosis behavior.
What is apocytosis?
It is a secretion mode of apocrine glands and mainly affects the mammary gland. Glandular cells secrete their secretions in different ways in the human body. In addition to merocrine and holocrine secretion, apocrine secretion is also one of the human secretion modes. In apocrine secretion, exocytosis takes place where vesicles inside a cell fuse with the cell membrane to release their secretion. Apocytosis refers to a special form of these exocytotic processes in apocrine gland cells. The secretion is thereby strangulated off together with a part of the gland cell membrane in containers. Regeneration allows this process to occur several times per cell despite membrane loss. Thus, both exocytosis and apocytosis are secretion modes of glands and gland cells. Exocytosis occurs rarely especially in human organism. The most characteristic example is the apozytotic fat droplet secretion of the mammary gland. Apart from the mammary gland, the secretion mode in humans is attributed exclusively to the scent glands and the ciliary glands. Medicine distinguishes specific from non-specific apocytosis. The nonspecific form is present when matrix vesicles are secreted with cytosol.
Function and role
Exocytosis is an important secretory mode of endocrine and exocrine gland cells. It gives rise to secretory vesicles with an average diameter of 50 nm, each enclosed by a double membrane. The gland cell releases the cellular contents of the vesicles into the lumen of its excretory duct. The secretory vesicles are usually formed in the Golgi apparatus of the cells. However, they may also detach from the endoplasmic reticulum or arise from endocytotic vesicles. In either case, the glandular cell transports the vesicles to its cell membrane, with which the vesicle membrane eventually fuses. Upon fusion, the cell membrane of the vesicles gives way and the contents of the vesicles are released. This process corresponds to exocytosis as it is present in numerous endocrine and exocrine gland cells and thus plays a role in hormone balance up to and including thermoregulation by sweating. Apocytosis is a special form of the described processes, which occurs much less frequently and mainly fulfills tasks in the nutrition of the offspring. This refers specifically to the specific apocytosis of the mammary gland. The secretory vesicles of the mammary gland cells correspond to fat droplets. Their production is stimulated by the sex hormones and the lactation hormone prolactin. The hormones bind to the receptors of the mammary gland cells and thus initiate apozytosis. Proteins attach to the outer surfaces of the fat droplets, binding to the integral proteins of the apical cell membrane. In this way, the fat droplet migrates to the lumen and its attached cell membrane bulges outward. On its way to the lumen, the membrane adapts to the shape of the vesicle, rounding and fusing underneath. In this way, the cell membrane constricts together with cytoplasm and the lipid droplets. The secretion is released from cytoplasm only by rupture of the surrounding membrane and vesicle. The cell thus loses volume during secretion as it releases its own cytoplasm and membrane components with the secretion. Thanks to their regenerative capacity, mammary gland cells are then in turn able to perform apocytosis several times despite the loss of volume.
Diseases and disorders
Scent glands and the mammary gland secrete a greasy secretion during apocytosis. Disturbances in the local acid mantle can make areas of these glandular cells vulnerable to bacterial infection and lead to abscess formation. Abscesses of the scent glands are often accompanied by fistula formation or inflammatory reactions. The condition is known as acne inversa and mainly affects adolescents during puberty. In the connective tissue of the affected area, sometimes extensive phlegmon form under the skin, which appear by a bluish discoloration and, depending on their extent, can cause sepsis. A common disease of the mammary gland is pathological milk discharge.This phenomenon may occur on one or both sides. Independently of pregnancy, the glands undergo apocytosis and release a milky secretion through the milk ducts. The secretory gland disorder is also called galactorrhea. Usually, an abnormal hormonal balance is responsible for milk production, which stimulates the glands to produce apozytosis. In most cases, prolactin is specifically produced. This so-called hyperprolactinemia can be caused, for example, by medication or stress. More rarely, benign brain tumors are responsible for the production, which themselves release hormones. Tumor diseases can also affect the mammary gland itself. This phenomenon also manifests itself under certain circumstances in altered apocytosis behavior, especially in absent apocytosis after pregnancy. However, this phenomenon should not be confused with absence of milk flow after pregnancy. If one or both mammary glands are not producing milk, apocytosis may still occur in the glandular tissue. In most cases, the cause of the lack of flow is simply a so-called milk stasis. In this case, skin overgrows the opening of the milk ducts and the secreted drops accumulate in the excretory ducts. In addition to hormonal balance, nutrition and psyche also play a role in milk production. Therefore, decreased milk flow after pregnancy should not automatically be interpreted as a worrisome scenario.
