Histophysiology of the secretory region
Cell renewal occurs continuously within the alveoli of sebaceous glands. It is highly dynamic: cells originate at the periphery of the secretory region and then gradually migrate. This vector of movement is directed from the basement membrane toward the central part of the alveolus and further directly to the opening of the excretory duct.
It is precisely due to this continuous displacement that uninterrupted secretion production is ensured, as destroyed structures are constantly replaced by newly differentiating cellular elements.
Stages of sebocyte differentiation
As they progress from the peripheral regions to the center, cells go through several successive stages of development. In histology, three main cell types are distinguished, reflecting their life cycle stages:
- Cambial (stem) sebocytes. These are relatively small cells located at the very periphery of the alveolus, lying directly on the basement membrane. Their main function is continuous division and providing a pool for differentiation into the next cell type.
- Secretory sebocytes. These cells have already shifted away from the basement membrane and are located closer to the center of the alveolus. They are characterized by large sizes. A distinct feature of these cells is a honeycomb (or foamy) appearance of the cytoplasm, caused by the active accumulation of sebum droplets consisting of lipids.
- Degenerating sebocytes. Located in the very center of the alveolus, directly near the opening of the excretory duct. It is at this stage that the holocrine type of secretion is implemented, in which the cells undergo complete destruction.
Mechanism of holocrine secretion
The essence of the holocrine process is that the release of secretion is impossible without the total destruction of the secreting cell itself.
In the part of the alveolus adjacent to the excretory duct, degenerating sebocytes accumulate. They are characterized by dense, hyperchromatic nuclei, indicating terminal changes in the cell. As a result of these processes, a complex mixture enters the excretory duct. It consists of the remnants of completely destroyed cells and the lipid droplets they accumulated—this mass constitutes sebum.
Briefly: answers to topical questions
From which embryonic germ layer do sebaceous glands develop?
Sebaceous glands develop from the surface ectoderm. During embryogenesis, a bilayered epithelium forms from the ectoderm and differentiates in the follicular direction.
The process includes the following stages:
- Formation of hair follicles.
- Formation of two types of buds on the follicle.
- Development of sebaceous and apocrine sweat glands from these buds.
Thus, the source of sebaceous glands is the ectodermal epithelium associated with hair morphogenesis.
What hormones regulate the activity and secretion of sebaceous glands?
The activity and secretion of sebaceous glands are regulated by sex hormones.
By sources:
- Testosterone stimulates terminal differentiation of sebocytes and sebum production.
- Progesterone stimulates terminal differentiation of sebocytes and sebum production.
- Androgen excess is associated with oily skin, acne, folliculitis, enlarged pores, and hirsutism.
The skin and its appendages, including sebaceous glands, are target tissues for sex hormones.
The term "holocrine" is easy to remember via the Greek root "holos" (whole, entire). The cell gives itself "entirely," completely destroying itself to form the secretion.
Class and exam questions
What is the main feature of holocrine secretion?
The main feature is the complete destruction of glandular cells. Their remnants, together with accumulated intracellular substances, form the secretion itself.
Where are cambial cells located in the sebaceous gland?
Cambial (stem) sebocytes are located at the periphery of the alveolus, directly on the basement membrane.
Why does the cytoplasm of secretory sebocytes appear honeycomb-like?
The honeycomb or foamy appearance of the cytoplasm arises due to intense intracellular accumulation of lipid droplets (sebum).
What do cell nuclei look like at the final stage of secretion?
In degenerating sebocytes located near the excretory duct opening, nuclei become very dense and hyperchromatic.
What else to study on this topic
- Morphology and functions of cambial cells
- The process of lipid accumulation in the cytoplasm of sebocytes
- Structure of the alveolar basement membrane
- Changes in the nuclear apparatus (formation of hyperchromatic nuclei)
- Histological structure of excretory ducts
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