Sweat gland
Encyclopedia
Sweat glands, or sudoriferous glands, are small tubular structures of the skin
that produce sweat
. There are two kinds of sweat glands:
Both apocrine and eccrine sweat glands contain myoepithelial cells (from Greek myo-, "muscle"), specialized epithelial cells located between the gland cells and the underlying basal lamina. Myoepithelial cell contractions squeeze the gland and discharge the accumulated secretions. The secretory activities of the gland cells and the contractions of myoepithelial cells are controlled by both the autonomic nervous system and by the circulating hormones.
Ceruminous glands
, which produce ear wax, and mammary glands, which produce milk, are frequently considered to be modified sweat glands, but they are not. Both ceruminous and mammary glands are true apocrine
glands.
method of secretion. Although it is now known that their secretory products are produced through merocrine
secretion, the name has not changed. Apocrine sweat glands are coiled tubular glands that produce a viscous, cloudy and potentially odorous secretion. Apocrine sweat glands discharge in the canals of hair follicles. They begin secreting at puberty; the sweat produced may be acted upon by bacteria, causing a noticeable odor. Apocrine gland secretions may also contain pheromones, chemicals that communicate information to other individuals by altering their hormonal balance. Some research has indicated that the apocrine secretions of mature women can alter the menstrual timing of other women (this is called the McClintock effect
), though the research methods used have been criticized. The significance of human pheromones, and the role of apocrine secretions in humans, remains not completely understood.
The clear secretion produced by eccrine sweat glands is termed sweat
or sensible perspiration. Sweat is mostly water, but it does contain some electrolytes, since it is derived from blood plasma
, although less concentrated. It therefore contains mainly sodium chloride
, but also other electrolytes. The presence of sodium chloride gives sweat a salty taste. The total volume of sweat produced depends on the number of functional glands and the size of the surface opening. The degree of secretory activity is regulated by neural and hormonal mechanisms (men produce greater volumes of sweat than women). When all of the eccrine sweat glands are working at maximum, the rate of perspiration for a human being may exceed three liters per hour, and dangerous fluid and electrolyte losses can occur. For this reason athletes in endurance sports must pause frequently to drink electrolyte-containing fluids.
Eccrine glands have three primary functions:
Skin
-Dermis:The dermis is the layer of skin beneath the epidermis that consists of connective tissue and cushions the body from stress and strain. The dermis is tightly connected to the epidermis by a basement membrane. It also harbors many Mechanoreceptors that provide the sense of touch and heat...
that produce sweat
SWEAT
SWEAT is an OLN/TSN show hosted by Julie Zwillich that aired in 2003-2004.Each of the 13 half-hour episodes of SWEAT features a different outdoor sport: kayaking, mountain biking, ice hockey, beach volleyball, soccer, windsurfing, rowing, Ultimate, triathlon, wakeboarding, snowboarding, telemark...
. There are two kinds of sweat glands:
- Eccrine sweat glandsEccrine sweat glandsEccrine glands are the major sweat glands of the human body, found in virtually all skin.. They produce a clear, odorless substance, consisting primarily of water and NaCl . NaCl is reabsorbed in the duct to reduce salt loss...
are found only in primatePrimateA primate is a mammal of the order Primates , which contains prosimians and simians. Primates arose from ancestors that lived in the trees of tropical forests; many primate characteristics represent adaptations to life in this challenging three-dimensional environment...
s and reach their greatest development in humanHumanHumans are the only living species in the Homo genus...
s. They are distributed all over the body (except for the lips, tip of penis and clitoris) although their density varies from region to region. Humans utilize eccrine sweat glands as primary form of coolingThermoregulationThermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different...
. The human thermal eccrine system has evolved in concert with bipedalism and development of smooth hairless skin. - Apocrine sweat glandsApocrine sweat glandsApocrine sweat glands are sweat glands composed of a coiled secretory portion located at the junction of the dermis and subcutaneous fat, from which a straight portion inserts and secretes into the infundibular portion of the hair follicle...
are larger, have different mechanism of secretion, and are limited to axilla (armpits) and perianal areas in humans. Although apocrine glands contribute little to cooling in humans, they are the only effective sweat glands in hoofed animals such as the donkey, cow, horse, and camel. Most other mammals, such as cats, dogs and pigs, rely on panting or other means for thermal regulation and have sweat glands only in foot pads and snout. The sweat produced on pads of paws and on palms and soles mostly serves to increase friction and enhance grip.
Both apocrine and eccrine sweat glands contain myoepithelial cells (from Greek myo-, "muscle"), specialized epithelial cells located between the gland cells and the underlying basal lamina. Myoepithelial cell contractions squeeze the gland and discharge the accumulated secretions. The secretory activities of the gland cells and the contractions of myoepithelial cells are controlled by both the autonomic nervous system and by the circulating hormones.
Ceruminous glands
Ceruminous glands
Ceruminous glands are specialized sudoriferous glands located subcutaneously in the external auditory canal. They produce cerumen or earwax which lubricates and cleans the auditory canal, and serves as a barrier to trap foreign particles...
, which produce ear wax, and mammary glands, which produce milk, are frequently considered to be modified sweat glands, but they are not. Both ceruminous and mammary glands are true apocrine
Apocrine
Apocrine is a term used to classify exocrine glands in the study of histology. Cells which are classified as apocrine bud their secretions off through the plasma membrane producing membrane-bound vesicles in the lumen. This method is also called decapitation secretion...
glands.
Apocrine sweat glands
The name apocrine was originally chosen because it was believed that the gland cells used an apocrineApocrine
Apocrine is a term used to classify exocrine glands in the study of histology. Cells which are classified as apocrine bud their secretions off through the plasma membrane producing membrane-bound vesicles in the lumen. This method is also called decapitation secretion...
method of secretion. Although it is now known that their secretory products are produced through merocrine
Merocrine
Merocrine is a term used to classify exocrine glands and their secretions in the study of histology. A cell is classified as merocrine if the secretions of that cell are excreted via exocytosis from secretory cells into an epithelial-walled duct or ducts and thence onto a bodily surface or into the...
secretion, the name has not changed. Apocrine sweat glands are coiled tubular glands that produce a viscous, cloudy and potentially odorous secretion. Apocrine sweat glands discharge in the canals of hair follicles. They begin secreting at puberty; the sweat produced may be acted upon by bacteria, causing a noticeable odor. Apocrine gland secretions may also contain pheromones, chemicals that communicate information to other individuals by altering their hormonal balance. Some research has indicated that the apocrine secretions of mature women can alter the menstrual timing of other women (this is called the McClintock effect
McClintock effect
Menstrual synchrony is a phenomenon reported in 1971 wherein the menstrual cycles of women who lived together reportedly became synchronized over time...
), though the research methods used have been criticized. The significance of human pheromones, and the role of apocrine secretions in humans, remains not completely understood.
Eccrine sweat glands
Eccrine sweat glands are smaller than apocrine sweat glands, and they do not extend as deep into the dermis. Eccrine sweat glands are coiled tubular glands that discharge their secretions directly onto the surface of the skin. Their density varies greatly according to body regions, the highest density (>250 glands/cm2) being on soles, palms, and scalp.The clear secretion produced by eccrine sweat glands is termed sweat
SWEAT
SWEAT is an OLN/TSN show hosted by Julie Zwillich that aired in 2003-2004.Each of the 13 half-hour episodes of SWEAT features a different outdoor sport: kayaking, mountain biking, ice hockey, beach volleyball, soccer, windsurfing, rowing, Ultimate, triathlon, wakeboarding, snowboarding, telemark...
or sensible perspiration. Sweat is mostly water, but it does contain some electrolytes, since it is derived from blood plasma
Blood plasma
Blood plasma is the straw-colored liquid component of blood in which the blood cells in whole blood are normally suspended. It makes up about 55% of the total blood volume. It is the intravascular fluid part of extracellular fluid...
, although less concentrated. It therefore contains mainly sodium chloride
Sodium chloride
Sodium chloride, also known as salt, common salt, table salt or halite, is an inorganic compound with the formula NaCl. Sodium chloride is the salt most responsible for the salinity of the ocean and of the extracellular fluid of many multicellular organisms...
, but also other electrolytes. The presence of sodium chloride gives sweat a salty taste. The total volume of sweat produced depends on the number of functional glands and the size of the surface opening. The degree of secretory activity is regulated by neural and hormonal mechanisms (men produce greater volumes of sweat than women). When all of the eccrine sweat glands are working at maximum, the rate of perspiration for a human being may exceed three liters per hour, and dangerous fluid and electrolyte losses can occur. For this reason athletes in endurance sports must pause frequently to drink electrolyte-containing fluids.
Eccrine glands have three primary functions:
- Thermoregulation. Sweat cools the surface of the skin and reduces body temperature.
- Excretion. Eccrine sweat gland secretion can also provide a significant excretory route for water and electrolytes, as well as for a number of prescription and nonprescription drugs .
- Protection. Eccrine sweat gland secretion aids in preserving the skin's acid mantleAcid mantleThe acid mantle is a very fine, slightly acidic film on the surface of the skin acting as a barrier to bacteria, viruses and other potential contaminants that might penetrate the skin. The pH of the skin is between 4.5 and 6.2, so it is acidic...
, which helps protect the skin from colonisation from bacteria and other pathogenic organisms.