An apocrine sweat gland (; from Greek ''apo'' 'away' and ''krinein'' 'to separate') is composed of a coiled secretory portion located at the junction of the

dermis The dermis or corium is a layer of skin between the epidermis (skin), epidermis (with which it makes up the cutis (anatomy), cutis) and subcutaneous tissues, that primarily consists of dense irregular connective tissue and cushions the body from s ...

and subcutaneous fat, from which a straight portion inserts and secretes into the infundibular portion of the

hair follicle The hair follicle is an organ found in mammalian skin. It resides in the dermal layer of the skin and is made up of 20 different cell types, each with distinct functions. The hair follicle regulates hair growth via a complex interaction betwee ...

. In humans, apocrine sweat glands are found only in certain locations of the body: the axillae (armpits),

areola The human areola (''areola mammae'', or ) is the pigmented area on the breast around the nipple. More generally, an areola is a small circular area on the Human body, body with a different histology from the surrounding Tissue (biology), tissue ...

and

nipple The nipple is a raised region of tissue on the surface of the breast from which, in lactating females, breast milk, milk from the mammary gland leaves the body through the lactiferous ducts to Breastfeeding, nurse an infant. The milk can flow th ...

s of the breast,

ear canal The ear canal (external acoustic meatus, external auditory meatus, EAM) is a pathway running from the outer ear to the middle ear. The adult human ear canal extends from the auricle to the eardrum and is about in length and in diameter. S ...

, eyelids, wings of the

nostril A nostril (or naris , : nares ) is either of the two orifices of the nose. They enable the entry and exit of air and other gasses through the nasal cavities. In birds and mammals, they contain branched bones or cartilages called turbinates ...

, perineal region, and some parts of the external genitalia. Modified apocrine glands include the ciliary glands (glands of Moll) in the eyelids; the ceruminous glands, which produce ear wax; and the mammary glands, which produce

milk Milk is a white liquid food produced by the mammary glands of lactating mammals. It is the primary source of nutrition for young mammals (including breastfeeding, breastfed human infants) before they are able to digestion, digest solid food. ...

. They are distinct from eccrine sweat glands, which cover the whole body. Most non-primate mammals, however, have apocrine sweat glands over the greater part of their body. Domestic animals such as dogs and cats have apocrine glands at each hair follicle and even in their urinary system, but eccrine glands only in foot pads and snout. Their apocrine glands, like those in humans, produce an odorless, oily, opaque secretion that gains its characteristic odor upon bacterial decomposition. Eccrine glands on their paws increase friction and prevent them from slipping when fleeing from danger.

Structure

The apocrine gland is made up of a glomerulus of secretory tubules and an excretory duct that opens into a hair follicle; on occasion, an excretory duct opens to the skin surface next to the hair. The gland is large and spongy, located in the subcutaneous fat deep in the dermis, and has a larger overall structure and lumen diameter than the eccrine sweat gland. The secretory tubules of apocrine glands are single layered, but unlike the eccrine secretory tubules, contain only a single type of ductal epithelial cell, varying in diameter according to their location, and sometimes branching off into multiple ducts. The tubules are wrapped in

myoepithelial cell Myoepithelial cells (sometimes referred to as myoepithelium) are cells usually found in glandular epithelium as a thin layer above the basement membrane but generally beneath the lumen (anatomy), luminal cells. These may be positive for ACTA2, alph ...

s, which are more developed than in their eccrine gland counterparts.

Sweating

In hoofed animals and marsupials, apocrine glands act as the main thermoregulator, secreting watery sweat. For most mammals, however, apocrine sweat glands secrete an oily (and eventually smelly) compound that acts as a

pheromone A pheromone () is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting like hormones outside the body of the secreting individual, to affect the behavio ...

, territorial marker, and warning signal. Being sensitive to

adrenaline Adrenaline, also known as epinephrine, is a hormone and medication which is involved in regulating visceral functions (e.g., respiration). It appears as a white microcrystalline granule. Adrenaline is normally produced by the adrenal glands a ...

, apocrine sweat glands are involved in emotional sweating in humans (induced by anxiety, stress, fear, sexual stimulation, and pain). In a five-month-old human in utero, apocrine glands are distributed all over the body; after a few weeks, they exist in only restricted areas, including the armpits and external genitalia. They are inactive until stimulated by hormonal changes in

puberty Puberty is the process of physical changes through which a child's body matures into an adult body capable of sexual reproduction. It is initiated by hormonal signals from the brain to the gonads: the ovaries in a female, the testicles i ...

Mechanism

The apocrine gland secretes an oily fluid with

proteins Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, re ...

and

lipids Lipids are a broad group of organic compounds which include fats, waxes, sterols, fat-soluble vitamins (such as vitamins Vitamin A, A, Vitamin D, D, Vitamin E, E and Vitamin K, K), monoglycerides, diglycerides, phospholipids, and others. The fu ...

that is odorless before microbial activity. It appears on the skin surface mixed with

sebum A sebaceous gland or oil gland is a microscopic exocrine gland in the skin that opens into a hair follicle to secrete an oily or waxy matter, called sebum, which lubricates the hair and skin of mammals. In humans, sebaceous glands occur ...

, as sebaceous glands open into the same hair follicle. Unlike eccrine sweat glands, which secrete continuously, the apocrine glands secrete in periodic spurts. Apocrine sweat glands were originally thought to use only apocrine secretion: vesicles pinch off from the secretory cells, then degrade in the secretory lumen, releasing their product. More recent research has shown that merocrine secretion also takes place. Myoepithelial cells form a smooth muscle lining around the secretory cells; when the muscles contract, they squeeze the secretory ducts and push out the accumulated fluid into the hair follicle. Sweat and

are mixed in the hair follicle and arrive mixed at the epidermal surface. The apocrine sweat is cloudy, viscous, initially odorless, and at a pH of 6–7.5. It contains water, protein,

carbohydrate A carbohydrate () is a biomolecule composed of carbon (C), hydrogen (H), and oxygen (O) atoms. The typical hydrogen-to-oxygen atomic ratio is 2:1, analogous to that of water, and is represented by the empirical formula (where ''m'' and ''n'' ...

waste material, and NaCl. The sweat only attains its characteristic odor upon being degraded by bacteria, which releases volatile odor molecules. More bacteria (especially corynebacteria) leads to stronger odor. The presence of axillary hair also makes the odor even more pungent, as secretions, debris, keratin, and bacteria accumulate on the hairs.

Prevalence

Non-primate mammals usually have apocrine sweat glands over most of their bodies. Horses use them as a thermoregulatory device, as they are regulated by adrenaline and more widely distributed on equines than in other groups. Skunks, on the other hand, use the glands to release a secretion that acts as a powerful defense mechanism. The "axillary organs", limited regions with equal numbers of apocrine and eccrine sweat glands, only exist in

human Humans (''Homo sapiens'') or modern humans are the most common and widespread species of primate, and the last surviving species of the genus ''Homo''. They are Hominidae, great apes characterized by their Prehistory of nakedness and clothing ...

s, gorillas, and

chimpanzee The chimpanzee (; ''Pan troglodytes''), also simply known as the chimp, is a species of Hominidae, great ape native to the forests and savannahs of tropical Africa. It has four confirmed subspecies and a fifth proposed one. When its close rel ...

s. In humans, the apocrine glands in this region are the most developed (with the most complex glomeruli). Men have more apocrine sweat glands than women in all axillary regions. There is currently no evidence that any sweat glands vary substantially by racial group, with most studies claiming to find variation being subject to methodological flaws.

References

Citations

Sources

* * * * * * *

External links

Diagram of eccrine and apocrine sweat glands
from Mayo Clinic {{DEFAULTSORT:Apocrine Sweat Gland Skin anatomy Glands Apocrine