Скачать или смотреть 3D Sweat Glands Embryology - Modes of Secretion of the Glands - Eccrine vs Apocrine Sweat Glands

Hello, I am Dr. Aizaz from MedicoVisual.com. In this highly visual 3D lecture, we explore the development of the sweat glands and the key concepts that make their differences easy to understand.

We begin with a concise, concept-oriented review of the modes of secretion in glands:

Merocrine secretion: secretory products are packaged by the Golgi into membrane-bound vesicles. These vesicles migrate to the cell membrane and release their contents by exocytosis. No part of the cell is lost.
Apocrine secretion: secretory products are interspersed in the apical cytoplasm. The apical “cap” buds off (decapitation), is lost, and later repaired; the cell does not die.
Holocrine secretion: secretory products fill the cell, the entire cell disintegrates, and its fragments act as the secretion. This involves sacrifice of the whole cell; the sebaceous gland is the classical example. Note that, according to some authors, secretory products may be membrane-bound even in apocrine/holocrine cells, though typically they are not.

Why this matters for sweat glands: we classically recognize two types—eccrine (the merocrine type) and apocrine sweat glands. Eccrine sweat glands do use merocrine secretion. Historically, apocrine sweat glands were thought to use apocrine secretion, but current understanding is that they also release their products via the merocrine mode. The nomenclature “apocrine sweat gland” persists as a historical misnomer, and the point remains slightly controversial among authors.

Embryology of eccrine (merocrine) sweat glands:

Origin: ectoderm. The epidermis is ectodermal; specifically, a solid ectodermal bud arises from the stratum basale.
A solid cord forms and coils into a gland. Centrally, cells undergo programmed cell death (apoptosis) to establish a lumen.
Peripheral cells differentiate into myoepithelial cells with long processes that help squeeze secretions outward. Importantly, these myoepithelial cells arise from the same ectodermal bud, not from surrounding mesenchyme.
The duct epithelium becomes a double-layered cuboidal epithelium.
To reach the surface, another bud from the stratum basale grows upward; some cells in its path die or relocate laterally, creating space for a spiraling duct that opens onto the skin surface as a pore. Eccrine glands thus pour their secretion directly onto the skin.

Embryology of apocrine sweat glands:

Origin: ectoderm-derived hair follicle epithelium (not directly from the stratum basale of the interfollicular epidermis).
A similar solid outgrowth forms, coils, undergoes central apoptosis to create a lumen, and develops myoepithelial cells.
Typically opens into the hair follicle within the pilosebaceous canal. Exceptionally, when no hair follicle is present, an apocrine gland may open directly onto the skin surface.

Structural organization and key differences:

Both are simple tubular coiled glands; mostly unbranched. Apocrine glands may sometimes be branched.
Lumen: eccrine have a narrow lumen; apocrine have a wider lumen.
Duct shape: eccrine ducts are highly coiled; apocrine ducts are relatively less coiled/less tortuous.
Opening: eccrine open directly onto the skin surface; apocrine usually open into the pilosebaceous canal.

Distribution:

Eccrine: almost everywhere, with high density on palms and soles.
Apocrine: localized—axilla, anogenital region, and areola of the breast (main sites highlighted).

Nature of secretions and odor:

Eccrine: thin, watery, hypotonic filtrate of blood with some salts; also carries small amounts of urea and ammonia. Typically lacks proteins and lipids.
Apocrine: hypotonic base but thick/viscous due to proteins and lipids. Initially odorless; bacterial breakdown of lipids later produces smell.

Functions and activation:

Eccrine: thermoregulation (cooling via sweating) and a minor excretory role (e.g., urea, ammonia, some salts).
Apocrine: release pheromones in animals; in humans, the exact function is not well understood, and the odor generally does not attract the opposite gender.
Onset: eccrine begin functioning immediately after birth; apocrine remain inactive until puberty, then become active under the influence of sex hormones in both genders.

Summary of origin:

Both eccrine and apocrine sweat glands (including their myoepithelial cells) are derived from ectoderm—eccrine from the stratum basale of the epidermis and apocrine from the epithelium of the hair follicle.

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