Sweat glands: definition, structure, function, embryology and clinical significance - Scope Heal (2023)

Basically we talk about integument appendages.

There are eccrine and apocrine sweat glands. They differ in embryology, distribution and function.

Thin skin covers most of the body and contains sweat glands as well as hair follicles, hair retraction muscles, and sebaceous glands.

Exceptions are the red border of the labia, external auditory canal, nail beds, glans, clitoris, and labia minora, which do not contain sweat glands.

The thick skin that covers the palms of the hands and soles of the feet lacks all of the skin appendages except the sweat glands.

Apocrine sweat glands, also known as odorous sweat glands, are known to produce malodorous sweat.

They are large, branching glands that are confined primarily to the axillary and perineal regions, including the perianal region, the labia majora in females, and the scrotum and foreskin in males.

Apocrine sweat glands are also present on the nipples and in the areolar tissue surrounding the nipples.

structure and function

The eccrine sweat glands fulfill a thermoregulatory function through the loss of heat by evaporation. When the body's internal temperature rises, the sweat glands release water to the surface of the skin.

There, it quickly evaporates, cooling the skin and blood underneath. This is the most effective means of thermoregulation in humans. The eccrine sweat glands are also involved in the excretion of nitrogenous ions and waste.

In response to emotional or thermal stimuli, the sweat glands can produce at least 500 ml to 750 ml per day.

The apocrine sweat glands begin to function at puberty under the stimulation of sex hormones. They are associated with hair follicles in the groin and underarm area.

The slimy, protein-rich product is initially odorless, but may develop an odor after exposure to bacteria.

Modified apocrine sweat glands include the wax-producing ceruminous glands of the external auditory meatus, Moll's glands found in the free margins of the eyelids, and the mammary glands of the breast.

Sweat glands play a regenerative role in skin damage. In second-degree skin burns that extend into the reticular dermis, regeneration of the epithelium occurs through the skin appendages, including hair follicles, sebaceous glands, and sweat glands.

The epithelial cells that surround these appendages produce more epithelial cells that progress to form new epithelium, a process that can take 1 to 3 weeks.

Embryology

Eccrine and apocrine sweat glands originate in the epidermis. Eccrine glands begin as buds of epithelial cells that grow into the underlying mesenchyme.

The glandular secretory components are then formed by elongating the gland and twisting the ends.

The primordial sweat ducts are formed by epithelial junctions of the developing gland. Eventually, the central cells degenerate to form the lumen of the sweat duct.

Cells at the periphery of the gland differentiate into secretory and myoepithelial cells.

Myoepithelial cells are believed to be specialized smooth muscle cells that expel sweat from the gland. Eccrine sweat glands first appear on the palms and soles during the fourth month of pregnancy; they become functional soon after birth.

On the other hand, the apocrine sweat glands do not function until hormonal stimulation during puberty and their ducts do not open on the surface of the skin. This is because these glands originate in the germinal layer of the epidermis.

Therefore, downward growth does not produce an open duct on the surface of the skin. Instead, the ducts open into the hair follicles and the sweat is released through the hair's opening in the skin.

The channels of these apocrine sweat gland ducts enter the superficial hair follicle in the sebaceous gland, resulting in protein-rich sweat rather than the watery sweat associated with eccrine sweat glands.

Blood and lymph supply

The sweat glands, along with all other skin appendages, receive their blood supply from skin perforators from underlying vessels of origin.

Perforators may branch directly from the source as septocutaneous or fasciocutaneous perforators or from muscular branches as musculocutaneous perforators.

Once these spikes reach the skin, they form extensive networks called the dermal and subdermal plexuses. The interconnections between these plexuses are formed by connecting vessels that run perpendicular to the surface of the skin, forming a continuous vascular plexus in the skin.

Lymphatic drainage parallels the blood supply, starting with blind lymphatic capillaries in the dermal papillae. These drain into the deep dermal and dermal plexuses which eventually coalesce to form larger lymph vessels.

nervous

Eccrine sweat glands receive sympathetic innervation via cholinergic fibers that send impulses in response to changes in core body temperature. Sympathetic innervation of the sweat glands is mediated by the thermoregulatory center of the hypothalamus.

A short preganglionic cholinergic fiber originates in the thoracolumbar region of the spinal cord and synapses on the postganglionic neuron via nicotinic acetylcholine.

The postganglionic fiber releases acetylcholine, which differs from all other sympathetic postganglionic fibers that release norepinephrine.

Cholinergic stimulation of muscarinic receptors induces sweating. The apocrine sweat glands receive adrenergic sympathetic innervation.

Because the apocrine sweat glands respond to norepinephrine, they are involved in emotional sweating due to stress, fear, pain, and sexual stimulation.

clinical significance

Given the role of sweat glands in thermoregulation, both eccrine and apocrine glands are associated with a variety of illnesses, from mild and uncomfortable to fatal.

Sweating disorders can have emotional, social and professional implications.

Hyperhidrosis is the excessive excretion of sweat beyond the amount required for thermoregulation. It may be idiopathic or due to other endocrine, neurological or infectious disorders.

Treatment options include topical medications, oral medications, surgical procedures, or botulinum toxin injection. Bromhidrosis is a similar disorder that manifests itself with excessive smelly sweating.

May involve apocrine or eccrine sweat glands; apocrine bromhidrosis tends to develop after puberty, while eccrine bromhidrosis can develop at any age.

It is caused by excessive sweating which secondarily becomes malodorous by bacterial decomposition. As poor hygiene often aggravates bromhidrosis, an effective treatment is to improve personal hygiene.

Surgical approaches, antibacterial agents, and antiperspirants are also treatment options.

The sweat glands of patients with cystic fibrosis (CF) are not effective in reabsorbing salt, which has important implications.

CF is an autosomal recessive congenital disease in which the cystic fibrosis transmembrane regulator (CFTR) that normally inhabits the apical membrane of epithelial cells is defective.

CFTR is a transmembrane protein that functions as part of a cAMP-regulated chloride ion channel; in normal sweat glands, the ductal epithelium reabsorbs sodium and chloride ions in response to aldosterone, making sweat hypotonic.

In CF patients, the sweat glands do not reabsorb chloride, which affects sodium reabsorption, resulting in salty sweat and the inability of the sweat glands to participate in ionic regulation.

Disruption of the same membrane proteins in the respiratory and gastrointestinal epithelium produces thick mucus accumulations.

Another autosomal recessive congenital disorder that affects the sweat glands is lamellar ichthyosis. Babies with persistent scaly skin and hair growth may be reduced.

Impaired development of the sweat glands often causes babies to suffer in extremely hot climates as they are unable to maintain thermoregulation through sweating.

Hidradenitis suppurativa is a chronic inflammatory disease that affects the hair follicles. This medical condition has classically been associated with apocrine sweat glands as it manifests after puberty in concentrated areas of the apocrine gland.

However, the pathophysiology involves follicular occlusion rather than the apocrine disorder, as previously thought. Patients usually present with subcutaneous and suppurative nodules and abscesses in the armpits and groin. Lesions can form extensive sinus tracts and scarring.

Hypohidrotic ectodermal dysplasia is a condition characterized by hypotrichosis (decreased growth of the scalp and body hair), hypodontia (congenital absence of teeth) and hypohidrosis.

The term “hypohidrotic” indicates impaired ability to perspire. Patients born with hypohidrotic ectodermal dysplasia have difficulty regulating body temperature and therefore must learn to modify their environment to control heat exposure.