The mechanism of action of sweat glands in the body

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Sweat glands, derived from the Latin word sudor meaning 'sweat', are small tubular structures of the skin that secrete sweat. The sweat gland is a type of exocrine gland, which produces and secretes sweat to the epithelial surface by means of a duct. Sweat in the body is produced with many different roles. The article will help answer the question of how sweat glands work.

1. Overview of sweat glands in the body

There are two main types of sweat glands that differ in structure, function, secretion products, excretory mechanisms, anatomy and distribution among species including:
Eccrine sweat glands are the more common type. present in many locations throughout the human body with different densities. Eccrine sweat glands appear most on the palms and soles, then on the scalp, and at least on the trunk and extremities. They excrete water-based sweat that plays a fundamental cooling role in the body.
Apocrine sweat glands are mainly limited to the armpit and perianal region in humans. They are not meant for cooling, but are the only effective sweat glands in hoofed animals, such as camels, donkeys, horses, and cattle.
Other types of ducts such as the sebaceous glands that produce earwax, the mammary glands that produce milk, and the glands in the eyelids are modified apocrine sweat glands.

2. Structure of a sweat gland

Each sweat gland consists of 2 basic parts, an excretory unit and a sweat duct. The excretory unit is located deep in the dermis and subdermis, and the entire gland is surrounded by adipose tissue. In both types of sweat glands, the secretory coils are surrounded by contractile epithelial cells that function to facilitate secretion of the secretory product. The sweat glands secrete and contract to expel sweat into the ducts which are regulated by the autonomic nervous system and by a number of hormones in the body.
Each sweat gland receives a number of nerve fibers that branch into bands of one or more axons and surround the individual ducts of the excretory core. In addition, the structure of sweat glands also includes small capillaries that are interwoven between sweat ducts.

3. Distribution of sweat glands on the body

The number of sweat glands varies widely from person to person, although comparisons between different regions (eg, armpits and groin) show similar distribution trends (some areas are always present). more sweat glands are active while others are always less). According to estimates by Henry Gray, the palm has about 370 sweat glands per square centimeter; the back of the hand has 200 glands/cm2; forehead has 175 glands/cm2; breast, abdomen and forearm have 155 glands per cm2; while the back and legs have 60–80 per cm2.
In the fingers, the pores of the sweat glands are unevenly spaced on the epidermal ridges. There are no pores between the ridges, although sweat tends to seep into them. The thick cuticles of the palms and soles cause the sweat glands to coil in a spiral.

4. Classification of sweat glands in the body

Types of eccrine glands
Eccrine sweat glands are located all over the body except for the ear canal, lips, glans penis, vulva and clitoris. The size of the eccrine glands is many times smaller than that of the apocrine sweat glands, does not extend deep into the dermis, and excretes sweat directly to the surface of the skin. The proportion of eccrine glands decreases with age.
The secretions produced by the sweat glands are called sweat. Sweat is composed mainly of water, but it does contain some electrolytes, as it is derived from plasma. The presence of sodium chloride gives sweat a salty taste.
The total amount of sweat secreted depends on the number of functional glands and the size of the surface. Secretory activity is regulated by neurological and hormonal mechanisms. When all the sweat glands in the body are working at full capacity, a person's sweat rate can exceed three liters per hour, so fluid and electrolyte loss can occur. danger to life. Men sweat more than women.
The eccrine sweat glands have three main functions:
Heat regulation: perspiration (through evaporation and heat loss by evaporation) can lead to cooling of the skin surface and a decrease in body temperature. Excretion: excretory eccrine sweat glands can also remove significant amounts of water and electrolytes. Protection: the sweat secreted by the sweat glands helps to preserve the acidic layer of the skin, which helps to protect the skin from colonization by bacteria and other disease-causing organisms. Apocrine sweat glands
Apocrine sweat glands are found in the armpits, areola, perineum, the area between the anus and genitals, in the ears, and in the eyelids. The excretory part of the apocrine glands is larger in size and makes them larger overall when compared to the eccrine glands. Instead of pouring directly on the surface of the skin, the apocrine glands secrete sweat into the ducts of the hair follicles.
Before puberty, the apocrine sweat glands are inactive; Hormonal changes during puberty cause the glands to increase in size and begin to function. The secretion is thicker than sweat from the eccrine glands and provides nutrients for the bacteria on the skin: the breakdown of bacteria in sweat is what creates the odor. The apocrine sweat glands are most active during times of stress and sexual arousal.

Apocrine sweat glands
Some sweat glands cannot be clearly distinguished as apocrine or eccrine, because they have characteristics of both. That's why such sweat glands are called apoeccrine. They are larger than the eccrine glands, but smaller than the apocrine glands. Their excretory ducts have a narrow part similar to the secretory coils in the eccrine glands and a wide part reminiscent of the apocrine glands.
The apoeccrine type of sweat gland, found in the armpits and perianal area, has ducts that open to the surface of the skin. The apoeccrine glands are thought to be the result of development from the eccrine glands during puberty, and may account for up to 50% of all axillary glands. The apoeccrine glands secrete the most sweat, especially in the skin under the arms. The apoeccrine glands are sensitive to cholinergic activity, although they can also be activated through adrenergic stimulation. Like the eccrine glands, they continuously secrete a thin, watery sweat.
Specialized sweat glands, including the cervical, mammary, lacrimal, and vestibular glands of the nose, are modified apocrine glands. The sweat glands have surface hairs near the ear canal and produce earwax by mixing with the oil secreted by the sebaceous glands. The mammary glands use apocrine secretion to produce milk.

5. How do sweat glands work?

The sweat glands regulate temperature and remove waste by secreting water, sodium salts, and nitrogenous wastes (such as urea) to the surface of the skin. The main electrolytes of sweat are sodium and chloride, although the amounts are small enough to render sweat hypotonic on the surface of the skin.
Sweat from the eccrine glands is clear, odorless and composed of 98–99% water. Some of the other ingredients include NaCl, fatty acids, lactic acid, citric acid, ascorbic acid, urea, and uric acid. Eccrine gland sweat has a pH that ranges from 4 to 6.8. Meanwhile, sweat from the apocrine glands has a pH between 6 and 7.5; Contains lots of water, protein, carbohydrates, lipids and steroids. Sweat is oily, cloudy, viscous and initially odorless; It has an odor when it is decomposed by bacteria. Because both the apocrine and sebaceous glands are open to the hair follicle, apocrine sweat mixes with sebum.
Both apocrine and eccrine sweat glands use merocrine secretion, where vesicles in the gland secrete sweat through exocytosis, leaving the entire cell intact. Initially, it was thought that the secretory activity of apocrine sweat glands was due to structures resembling "separators" on the cell surface, however, recent electron microscopy images only found that cells use secretion in a merocrine fashion. In most glands, sweat is initially produced in the gland's coil, which is isotonic with the plasma in place. When the rate of perspiration decreases, salt is conserved and reabsorbed by the ducts; On the other hand, a high perspiration rate results in less salt reabsorption and allows more water to evaporate from the skin (via osmosis) for increased evaporation and cooling.
Sweat secretion occurs when the epithelial cells surrounding the secretory glands contract. Exudative sweat accelerates bacterial growth and evaporates the odorous compounds of apocrine sweat, producing the characteristic body odor. Normally, only certain sweat glands in certain locations maintain sweat production. When profuse perspiration triggers are present, more sweat glands are activated, and each gland then secretes more sweat.
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Reference source: etiaxil.com.vn