Definition:
Sweat glands, or sudoriferous glands, are exocrine glands found under the skin in all mammal species which are used for body temperature regulation (thermoregulation).
Classification:
In humans, there are two kinds of sudoriferous or sweat glands which differ in both the composition of the sweat and its purpose:
Anatomy and Location:
Exocrine glands contain a glandular portion and a duct portion, the structures of which can be used to classify the gland:
- The duct portion may be branched (called compound) or unbranched (called simple).
- The glandular portion may be tubular, acinar, or may be a mix of the two (called tubuloacinar). If the glandular portion branches, then the gland is called a branched gland.
"Eccrine glands:":
- They are distributed over almost the entire surface of the body (99%) in humans and many other species, but are lacking in some marine and fur-bearing species.
- They concentrate more on plant, palm, forehead and chest. They lack at level of the lip pseudomucosa, of glans and internal leaflet of the prepuce, of the little lips and the face interns of auricular pavilion. Their number is included between 2 and 5 millions, the number is different according to the individual corporeal area and perspiration rate.
- Anatomy:
- they are coiled tubular glands
- The structure of the eccrine sweat gland consists of a bulbous secretory coil leading to a duct. The secretory coil is located in the lower dermis, and the duct extends through the dermal layer and opens directly onto the skin surface. The uncoiled dimension of the secretory portion of the gland approximates 30 – 50 µm in diameter and 2 – 5 mm in length. The size of the adult secretory coil ranges" from 1 to 8 ×10 – 3 mm3. There is a positive correlation between the size of an individual sweat gland and the maximal sweat rate of that gland.
- The secretive glomerule is formed by 3 cellular types:
- clear cell, peripheral, rich in glycogen
- dark cell, oriented towards the duct, rich in mucopolysaccarides
- myoepiothelial cells, they receive cholinergic stimulus
- You can find them only in the zones with hairs, they are mainly present in the armpits and around the genital area
- Anatomy:
- They are coiled tubular glands
- The deep portion is localizated in the deep derm and connects to the 3rd superior of the piliferous follicle.
- The secretory component consists of a simple epithelium surrounding a large lumen which stores the secretion. Myoepithelial cells found along the basement membrane move the secretion through the lumen. The duct component is a stratified cuboidal epithelium that runs straight to the infundibulum of the hair follicle; the duct does not modify the secretion.
Secretion:
There are two times in the sweat production
- at level of glomerule where the "primary a hypotonic solution of NaCl is produced
- in the duct where Na, Cl and water are partly reabsorbed:the reabsorbement also results from the speed of perspiration
Eccrine glands:
- Mechanism:they secrete in an merocrine fashion.
- Control: by sympathetic cholinergic nerves which are controlled by a centre in the hypothalamus. The hypothalamus senses core temperature directly, and also has input from temperature receptors in the skin and modifies the sweat output, along with other thermoregulatory processes.
- Composition of eccrine sweat:
Apocrine glands:
- Mechanism:they secrete in an merocrine fashion.
- Control: Like eccrine sweat glands, they are under control of the sympathetic nervous system but are stimulated by adrenergic transmitters
- Composition:
- They produce a semi-viscous fluid which contains: Thick, milky fluid, protein, ammonia, lipids, chromogranins (family of proteins) and they also produce proteins equivalent to pheromones.
in non-human mammalian species
- Bacterial decomposition of sweat components leads to odor (a situation called Bromidrosis)
Stimulus for secretion:
- Temperature control: To convert water from a liquid to a vapor, it takes a certain amount of heat called the heat of vaporization. This heat energy increases the speed of the water molecules so that they can escape into the air. For water, this value is 540 calories/gram or 2.26 × 106 joules/kilogram. So, if you can produce one liter of sweat, which is equal to 1000 g or 1 kg (density of water is 1 g/ml or 1 kg/l) in one hour, then 540,000 calories of heat can be removed from your body.
- Emotional state: when you are nervous, anxious or afraid, there is an increase in sympathetic nerve activity in the body as well as an increase in epinephrine secretion from adrenal glands. These substances act on your sweat glands and increases sweat secretion
- Exercise
- Capsaicine
