Holokrina

Holokrina is a term used in histology to describe a specific mode of glandular secretion. In holocrine secretion, the entire cell accumulates secretory products and then undergoes programmed cell death, or apoptosis. The cell disintegrates, releasing its contents into the lumen of the gland. This mechanism of secretion is distinct from merocrine and apocrine secretion, which involve the release of products without cell death.

The sebaceous glands of the skin are a classic example of holocrine glands. These glands produce sebum, an oily substance that lubricates the skin and hair. The cells of the sebaceous gland mature, fill with lipids, and then rupture to release the sebum. Other examples of holocrine glands include the meibomian glands in the eyelids, which secrete an oily lipid layer to prevent tear evaporation.

The process of holocrine secretion involves several stages. Initially, basal cells of the gland divide and differentiate. As these cells migrate towards the lumen, they accumulate lipid droplets and other secretory materials within their cytoplasm. Eventually, the cell membrane breaks down, and the entire cell, along with its contents, is shed as the secretion. This continuous process ensures a steady supply of the gland's product. The complete destruction and regeneration of the secretory cells is a defining characteristic of holocrine glands.