Sweat Glands

1. Overview

Sweat glands, also known as sudoriferous glands, are specialized exocrine glands of the integumentary system that produce and secrete sweat. Their primary function is thermoregulation through evaporative cooling, but they also play roles in excretion, skin hydration, and antimicrobial defense. There are two main types of sweat glands in humans: eccrine (merocrine) glands and apocrine glands. These glands are crucial for maintaining homeostasis, especially during heat exposure, physical exertion, and emotional stress.

2. Location

Sweat glands are distributed throughout the skin but vary in type and density based on body region:

• Eccrine sweat glands:

  • Found all over the body, especially abundant on the palms, soles, forehead, and axillae.

• Apocrine sweat glands:

  • Restricted to specific areas: axillae (armpits), areola of the breasts, perianal region, external genitalia, and eyelids (as modified glands).

Eccrine glands open directly onto the skin surface, whereas apocrine glands usually open into hair follicles.

3. Structure

Sweat glands are coiled tubular structures composed of two main parts:

• Secretory portion:

  • Located deep in the dermis or hypodermis; consists of a coiled glandular epithelium surrounded by myoepithelial cells.

• Duct portion:

  • Leads from the secretory coil to the skin surface or hair follicle; lined by stratified cuboidal epithelium.

Eccrine Glands

• Simple coiled tubular glands.

• Innervated by cholinergic fibers of the sympathetic nervous system.

Apocrine Glands

• Larger, less numerous glands.

• Begin functioning at puberty and are influenced by adrenergic stimuli.

• Produce a thicker secretion rich in proteins and lipids.

4. Function

Sweat glands serve a variety of essential functions:

• Thermoregulation: Sweat evaporation cools the body, especially during physical activity or heat exposure.

• Excretion: Helps eliminate small amounts of metabolic waste (e.g., urea, ammonia, electrolytes).

• Skin hydration: Maintains moisture balance of the stratum corneum, particularly by eccrine glands.

• Body odor generation: Apocrine secretions are metabolized by skin flora, producing characteristic scent.

5. Physiological role(s)

Beyond their immediate functions, sweat glands contribute to broader physiological processes:

• Homeostasis: Regulation of body temperature and water balance via evaporative cooling and electrolyte excretion.

• Immune defense: Sweat contains antimicrobial peptides such as dermcidin, which help protect against pathogens.

• Emotional signaling: Apocrine sweating increases during emotional stress, potentially playing a role in nonverbal communication.

• pH maintenance: Sweat contributes to the skin's acid mantle, inhibiting microbial overgrowth.

6. Clinical Significance

Sweat glands are involved in several dermatological and systemic conditions:

• Hyperhidrosis:

  • Excessive sweating, often localized to palms, soles, or axillae; can be idiopathic or secondary to systemic disease.

• Anhidrosis or hypohidrosis:

  • Reduced or absent sweating due to nerve damage, skin conditions, or genetic disorders, increasing risk of overheating.

• Miliaria (heat rash):

  • Blockage of sweat ducts leads to retention of sweat and inflammation, commonly seen in hot, humid environments.

• Bromhidrosis:

  • Foul-smelling body odor caused by bacterial decomposition of apocrine sweat; common in axillary and genital regions.

• Apocrine gland disorders:

  • Hidradenitis suppurativa: chronic inflammatory condition of apocrine gland-bearing areas, causing painful nodules and abscesses.

• Target for treatment:

  • Botulinum toxin (Botox) injections are used to block acetylcholine release and reduce excessive eccrine gland activity in hyperhidrosis.