SWEAT GLANDS: FUNCTION, TYPES AND DISEASES - ANATOMY AND PHYSIOLOGY - 2025

The sweat glands are external secretion glands, that is, they are exocrine glands. They are found in the skin of all mammals and their secretion product is shed towards the external surface of the same, directly or through the hair follicles.

A gland is a structure formed from epithelial cells that leave the surface where they form and penetrate the underlying connective tissue, forming a basal lamina. The glands are responsible for synthesizing and secreting various types of substances through secretory granules that accumulate in the cytosol of their cells.

Anatomy of the skin and location of the sweat glands (Source: Sheldahl via Wikimedia Commons)

According to the site to which these substances are secreted, the glands can be classified as exocrine and endocrine. The former release their secretions to the outside of the body (the skin, the intestine, the respiratory tract, etc.), while the endocrine ones do the same to the circulatory stream.

Since the sweat glands secrete their products towards the surface of the skin, they are classified in the group of exocrine glands. Two types of these glands are known: eccrine sweat glands and apocrine sweat glands, and they play important roles in thermoregulatory mechanisms.

Sweat gland function

The eccrine sweat gland function is subject to thermoregulation. The human being, as well as all mammals, from the point of view of body temperature, is a homeothermic organism, that is, it maintains its internal temperature constant despite fluctuating changes in environmental temperature.

The body uses the sweat glands as one of the main mechanisms of heat loss when increases in regulated temperature tend to occur (37 plus or minus 5 ° C).

These mechanisms of heat loss occur when the secretions of the sweat glands evaporate on the surface of the skin, a process that allows energy to be transformed and heat lost through evaporation.

Under extreme exercise conditions in hot environments, the secretions of the eccrine sweat glands can be so profuse that a human being can lose up to 10 liters of fluid this way.

The function of the apocrine sweat glands is related to sexual behavior, as these glands are related to olfactory sexual signals.

Types

Sweat glands can be of two types: eccrine and apocrine sweat glands. The main difference between both groups has to do with the secretion mode of their products.

Structure of the sweat gland ducts (Source: Kurata R., Futaki S., Nakano I., Fujita F., Tanemura A., Murota H., Sekiguchi K., Katayama I., Okada F. via Wikimedia Commons)

Eccrine sweat glands

These are the most abundant sweat glands on most of the skin's surface. They have a diameter of 0.4 mm and, in human skin, there are more than 3 million of these; Its secretion product consists of an aqueous solution (sweat).

In some mammals such as dogs, cats, cattle and sheep, the eccrine glands are restricted to the pads of the hind and front legs, and their function is to prevent the animal from slipping during flight and escape.

Their main function has to do with thermoregulation, since they are responsible for secreting a watery substance that allows heat to dissipate by evaporation from the body surface.

The eccrine glands are simple spiral tubular glands, located deep in the dermis or in the lower layer, the hypodermis. Inside, each eccrine gland has a thin spiral-shaped duct that runs through the dermis and epidermis and opens to the surface through a sweat pore.

This type of glands is characterized by its merocrine secretion mechanism, which means that its excretion product is expelled by exocytosis, so that neither the plasma membrane nor the cytosol of the cells that compose them are part of the secretion.

The eccrine glands are innervated by postganglionic nerve fibers of the sympathetic nervous system, which regulate their function.

Apocrine sweat glands

The distribution of the apocrine sweat glands is much more restricted than that of the eccrine glands.

In humans these glands are found mainly in areas where there is abundant hair, such as the armpits, the pubic and anal region, the scalp and the areoles of the nipples. In other mammals these glands are slightly more abundant.

Apocrine sweat glands are larger than eccrine glands; they measure approximately 3 mm in diameter and their secretory cells are simple cuboid cells. They are controlled by the autonomous system.

Unlike the eccrine glands, these glands discharge their secretion products into the hair follicles and it is through these that these secretions reach the surface of the skin. Its ducts open into the hair follicles in a more superficial position than the mouth of the sebaceous glands in those same follicles.

They are called apocrines because they release a small portion of the apical cytosol of your cells along with the product they secrete.

The secretory product of these glands consists of an odorless fatty solution, when it is secreted, but when it reaches the surface of the skin, local bacteria are able to metabolize it, producing odorous fatty acids that give it a characteristic aroma.

These glands, in humans, are "inactive" until puberty, when they are stimulated by hormonal action. Emotional stress causes the wall of the apocrine glands to contract, expelling their secretion.

The ceruminous glands of the external auditory canal and the Moll's glands of the eyelids are modified apocrine glands, as well as other specialized glands: the mammary and odoriferous glands of some animals.

Diseases

Pathologies related to the eccrine sweat glands can be:

Hyperhidrosis

It is an excess of sweating that is a reflection, in turn, of alterations of the autonomic nervous system.

Hypohidrosis

In hypohidrosis, the sweat glands reduce their secretory function. In these cases, there may be a risk of heat shock, which is a critical increase in body temperature due to a decrease in heat loss processes. This condition can lead to seizures and even death.

Miliaria or heat rashes

It is produced by the obstruction of the openings of the secretory ducts of the eccrine sweat glands, trapping the secreted product under the skin, causing the appearance of rashes in infants and adults under warm conditions.

Bromhidrosis

One of the most common conditions of the apocrine sweat glands is bromhidrosis, which is related to an exaggerated or abnormal body odor, a product of bacterial breakdown of the fats present in apocrine secretions.

This condition is not only due to some systemic defect, but it can also be due to poor body hygiene, physical activity and food consumed.

References

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2. Hall, JE (2015). Guyton and Hall textbook of medical physiology e-Book. Elsevier Health Sciences.
3. Hibbs, RG (1958). The fine structure of human eccrine sweat glands. American Journal of Anatomy, 103 (2), 201-217.
4. Quay, WB (1977). Structure and function of skin glands. In Chemical signals in vertebrates (pp. 1-16). Springer, Boston, MA.
5. Way, SC, & Memmesheimer, A. (1940). The Sudoriparous Glands: III. Sweat. Archives of Dermatology and Syphilology, 41 (6), 1086-1107.