Sweat glands
Glandulae sudoriferae
Also known as: sudoriferous glands, sudoriparous glands
Sweat glands are coiled tubular exocrine glands of the skin of two main types: widespread eccrine glands that produce watery sweat for cooling, and apocrine glands of the axillae and anogenital region that produce a protein-rich secretion.
Overview
Both types consist of a secretory coil deep in the dermis or hypodermis and a duct leading to the surface, but they differ in distribution, opening, secretion, control and age of onset.
Eccrine glands (≈2–4 million) occur over almost the entire body, densest on the palms, soles and forehead; they open directly onto the skin through a sweat pore, are active from birth, secrete a hypotonic, watery fluid and are controlled by sympathetic cholinergic fibres for thermoregulation (palmar, plantar and axillary glands also respond to emotion). Apocrine glands are confined to the axillae, areolae, perianal and genital regions; they have a wide lumen, open into the hair follicle above the sebaceous duct, become functional at puberty and secrete a viscous, protein- and lipid-rich fluid under adrenergic control that skin bacteria convert to body odour. Intermediate apoeccrine glands develop in the adult axilla.
Modified apocrine glands include the ceruminous glands of the external acoustic meatus, the ciliary glands of Moll in the eyelids and, by origin, the mammary gland.
Parts & subdivisions
- Merocrine, widespread, thermoregulatory, open via sweat pores.
- Axillary/anogenital, open into hair follicles, active from puberty.
- Modified apocrine glands of the external ear canal.
- Ciliary glands (of Moll)Modified apocrine glands opening into eyelash follicles; infection causes an external hordeolum (stye).
Anatomy
- Innervation
Sympathetic postganglionic fibres: cholinergic (muscarinic M3) to eccrine glands; adrenergic to apocrine glands and contributing to emotional sweating.
Function
- Evaporative heat loss (eccrine)
- Excretion of water, salts, urea and lactate (eccrine)
- Antimicrobial protection (dermcidin, acidic pH)
- Keeping palms and soles moist for grip (eccrine)
- Scent production and social signalling (apocrine)
Clinical significance
Hyperhidrosis and anhidrosis
Primary focal hyperhidrosis of palms, soles or axillae is treated with aluminium chloride, botulinum toxin (blocks ACh release) or thoracic sympathectomy. Loss of sweating (anticholinergics, autonomic neuropathy, extensive burns or scarring, ectodermal dysplasia) predisposes to heat stroke.
Test yourself
Eccrine sweat glands are stimulated mainly by which neurotransmitter?
- Noradrenaline acting on α1-adrenoceptors
- Acetylcholine released by sympathetic postganglionic fibres
- Acetylcholine released by parasympathetic fibres
- Adrenaline from the adrenal medulla
Answer: Acetylcholine released by sympathetic postganglionic fibres
Eccrine glands are innervated by sympathetic postganglionic fibres that are exceptionally cholinergic (ACh on muscarinic M3 receptors). The skin has no parasympathetic supply. This is why anticholinergic poisoning causes hot, dry skin.
Which statement about apocrine sweat glands is correct?
- They are found over the whole body surface
- They open directly onto the skin surface via a spiral duct
- They open into hair follicles and become active at puberty
- They are the main glands for thermoregulatory sweating
Answer: They open into hair follicles and become active at puberty
Apocrine glands are restricted to the axillae, areolae and anogenital region, empty into hair follicles above the sebaceous duct, become active at puberty under androgens and produce a protein-rich secretion that bacteria convert into body odour.
Compiled from standard anatomy and physiology references — see the Integumentary System sources. For education only; not medical advice.