Eccrine and Apocrine Glands
Donald J. Baker, M.D., and Warren R. Heymann, M.D.
Eccrine Glands
Eccrine glands begin to form during the fourth month of gestation as a downgrowth of the epidermis known as the eccrine germ. They first develop on the palms and soles, and then gradually appear on the remainder of the body, with the exception of the vermilion border of the lips, nail beds, labia minora, glans penis, and inner surface of the prepuce. The highest density of eccrine glands is seen on the palms, soles, and axillae. The eccrine germ later forms the three portions of the eccrine gland (Figure 1): the intraepidermal portion (acrosyringium), the intradermal duct (coiled and straight duct), and the secretory portion (coiled gland). The coiled gland is located in the deep dermis or at the border of the dermis and subcutaneous fat. It is composed of one distinct layer of clear and dark cells. The clear cells secrete glycogen, water, and electrolytes, and the dark cells secrete sialomucin. These secretory cells are surrounded by contractile myoepithelial cells enclosed within a hyaline basement membrane with peripheral collagen fibers. The eccrine duct extends upward from the coiled gland through the dermis, first as the coiled duct and then as the straight duct. The eccrine duct is composed of an outer layer of basal cells, and an inner layer of cells whose luminal surface forms an eosinophilic cuticle. The straight duct ends as it enters into a wide rete ridge of the epidermis, also known as an eccrine sweat duct ridge. The duct is now referred to as the acrosyringium as it spirals through the epidermis and opens directly onto the skin surface.
Eccrine sweat is produced via merocrine secretion in the coiled gland, and is composed of water, sodium, potassium lactate, urea, ammonia, serine, ornithine, citrulline, aspartic acid, heavy metals, organic compounds, and proteolytic enzymes. Acetylcholine production results in an increased calcium level in the secretory cell cytoplasm, followed by an intricate series of sodium, potassium, and chloride ion exchanges, which ultimately lead to sodium and chloride movement into the gland lumen. The initially isotonic eccrine sweat then travels through the eccrine duct where NaCl and HCO3 are actively reabsorbed. Only about 25 percent of the sodium can be reabsorbed. Eccrine sweat then passes through the acrosyringium and is deposited on the skin's surface.
The primary function of the eccrine unit is thermoregulation, which is accomplished through the cooling effects of evaporation of this sweat on the skin's surface. Stimulation of eccrine sweat production is mediated predominantly through postganglionic C fiber production of acetylcholine (Table 1). Emotional stressors tend to induce sweating that is confined mainly to the palms and soles. All eccrine units can be utilized to respond to the body's changing thermoregulatory needs.
Apocrine Glands
Apocrine glands are outgrowths of the superior portions of pilosebaceous units (hair follicles). The pilosebaceous unit forms throughout the fourth to sixth month, initially on the scalp, and then on the remainder of the skin's surface. A primary epithelial germ (hair germ) grows down from the epidermis and forms an apocrine gland, sebaceous gland, and hair follicle. Apocrine glands (Figure 2) consist of: (1) a coiled gland in the deep dermis or at the junction of the dermis and subcutaneous fat; and (2) a straight duct that traverses the dermis and empties into the isthmus (uppermost portion) of a hair follicle. The coiled gland consists of one layer of secretory cells around a lumen that is about 10 times the diameter of its eccrine counterpart. Contractile myoepithelial cells, a hyaline basement membrane, and connective tissue surround the coiled gland. The straight duct runs from the coiled gland to the isthmus of the hair follicle and is identical in appearance to the eccrine straight duct, with two cuboidal layers of cells encircling a lumen lined with an eosinophillic cuticle.
The predominant mode of apocrine secretion is decapitation, a process where the apical portion of the secretory cell cytoplasm pinches off and enters the lumen of the gland. Apocrine sweat consists mainly of sialomucin. Although odorless initially, as apocrine sweat comes in contact with normal bacterial flora on the surface of the skin, an odor develops. Apocrine sweat is more viscous and produced in much smaller amounts than eccrine sweat, (which actually is the wet portion of axillary sweat) (Table 1). The exact function of apocrine glands is unclear, although they are thought to represent scent glands.
At the time of birth, apocrine glands are present primarily in the axillae and anogenital regions, where they remain small and nonfunctional until puberty. Specialized variants of apocrine glands also exist: the Moll's glands seen on the eyelids; the cerumen-producing (ear wax) glands of the external auditory canal; and the milk-producing glands of the breasts. At puberty, hormonal stimulation causes apocrine glands to become functional, and they respond mainly to sympathetic adrenergic stimuli initiated by emotional stressors. Also during puberty, apoeccrine glands appear. They are hybrid sweat glands that are found in the axilla. Apoeccrine glands might play a role in axillary hyperhidrosis. Their secretory glands have both a small-diameter portion similar to an eccrine gland and a large-diameter portion that resembles an apocrine gland. Similar to eccrine glands, they respond mainly to cholinergic stimuli, and their ducts are long and open directly onto the skin's surface. However, apoeccrine glands secrete nearly 10 times as much sweat as eccrine glands.
Disorders of the Eccine Glands and Apocrine Glands
A variety of diseases are caused by or lead to abnormal function of the eccrine and apocrine glands. Hyperhidrosis, or excessive eccrine sweat secretion, can be generalized in certain systemic, central nervous system, or peripheral nervous system diseases. Localized hyperhidrosis of the palms and soles is often due to emotional stressors. Varying degrees of hyperthermia are associated with decreased eccrine sweating (hypohidrosis) or absent sweating (anhidrosis) in hereditary disorders such as the ectodermal dysplasias. Hypohidrotic ectodermal dysplasia, also known as Christ-Siemens-Touraine syndrome, is an X-linked recessive disease that consists of the triad of hypotrichosis, anodontia, and hypohidrosis, along with characteristic facies. Hidrotic ectodermal dysplasia, also known as Clouston's syndrome, is an autosomal dominant disorder with normal facial features and active eccrine glands, alopecia, nail dystrophy, eye changes, and palmoplantar hyperkeratosis. Hypohidrosis or anhidrosis can also be seen in acquired conditions like heat stroke or heat exhaustion. Patients with cystic fibrosis are unable to reabsorb sodium in the eccrine duct, and therefore they have elevated sodium concentrations in their eccrine sweat. A uremic frost, seen on the skin of patients with severe renal failure and markedly elevated serum urea levels, is the result of increased urea and salt deposits from the eccrine sweat.
Excessive heat and humidity that causes profuse eccrine sweating might sometimes be accompanied by blockage of the eccrine units with subsequent duct rupture and varying degrees of inflammation presenting as miliaria. If ductal obstruction occurs within the stratum corneum, then miliaria crystallina develops with asymptomatic superficial vesicles and no surrounding inflammation. When ductal obstruction is found deeper in the epidermis, then miliaria rubra (prickly heat) appears as pruritic or tender red macules or papules, which are often located on the thorax and neck. Prolonged exposure to tropical environments resulting in multiple episodes of miliaria rubra can lead to the development of miliaria profunda, with asymptomatic skin-colored papules forming as a result of eccrine duct obstruction at or below the dermoepidermal junction. Fox-Fordyce disease, or apocrine miliaria, develops when minor inflammation follows intraepidermal rupture of apocrine ducts. More intense inflammation due to follicular obstruction can secondarily involve the apocrine units in hidradenitis suppurativa. Multiple benign and malignant neoplasms also can originate in both eccrine and apocrine glands, the most common being benign syringomata on the lower eyelids of adult women.
References
- Schaller M and Plewig G. Structure and function of eccrine, apocrine, apoeccrine and sebaceous glands. In: Dermatology. Bolognia JL, Jorizzo JL, Rapini RP, et al., eds. Philadelphia: Mosby, 2003, pp.525-530.
- Murphy GF. Histology of the skin. In: Lever's Histopathology of the Skin. Elder D, et al., eds. Eighth edition, Philadelphia: Lippincott-Raven Publishers, 1997, pp. 24-28.
- Goldsmith LA. Biology of eccrine and apocrine sweat glands. In: Freedburg IM, Eisen AZ, Wolff K, et al, eds. Fitzpatrick's Dermatology in Internal Medicine. 6th ed. New York: McGraw-Hill; 2003: Chap8.
- Wenzel FG, Horn TD. Nonneoplastic disorders of the eccrine glands. J Am Acad Dermatol 1998, 38:1-17.
Figure Legends
Figure 1. The eccrine unit: Eccrine units consist of three portions: (1) the acrosyringium or intraepidermal spiralled duct; (2) the coiled and straight intradermal duct; and (3) the secretory coiled gland (from reference 1, with permission).
Figure 2. The apocrine unit: Apocrine units consist of a secretory coiled gland and a straight duct which traverses the dermis and empties into the isthmus (uppermost portion) of a hair follicle (from reference 1, with permission).
Table 1. Comparison of eccrine and apocrine glands
| Eccrine Glands | Apocrine Glands | |
| First appear | palms and soles | scalp |
| Highest density | palms, soles, axillae | axillae, anogenital |
| Gland lumen | smaller | 10x larger in diameter than eccrine gland lumen |
| Secretor | merocrine | decapitation secretion |
| Sympathetic Stimulation | cholinergic | adrenergic |
| Chemical composition of sweat | hypotonic saline | sialomucin |
| Ductal openings | directly onto skin surface | into isthmus of nail follicle |
| Primary function | thermoregulation | scent |
| Portion of axillary sweat | wet portion | odor portion |
Questions: Eccrine and Apocrine Glands
1. Where do eccrine glands develop first?
A) scalp
B) face
C) palms and soles
D) anogenital region
E) axillae
2. What percentage of secreted sodium can be reabsorbed in the eccrine duct?
A) 15%
B) 25%
C) 55%
D) 75%
E) 100%
3. What is another name for the apocrine glands of the eyelid?
A) Moll's glands
B) Meibomian glands
C) Montgomery's tubercles
D) Ceruminous glands
E) Lactiferous glands
4. Eccrine sweat consists of all of the following EXCEPT:
A) electrolytes
B) lactate
C) urea
D) lipofuscin
E) amino acids
5. An infant presents with weight loss and foul-smelling stools. The child is sent for a sweat test to confirm or rule out the diagnosis of:
A) hidrotic ectodermal dysplasia
B) anhidrotic ectodermal dysplasia
C) Crohn's disease
D) Cystic fibrosis
E) miliaria crystallina
Click here for answers.
