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Eccrine Glands
Eccrine sweat glands are simple coiled tubular glands distributed over most of the body surface. Their ducts open directly onto the epidermis, and their watery secretion is essential for evaporative cooling and thermoregulation.
Region-
SystemIntegumentary System
Eccrine glands, also called eccrine sweat glands, are simple coiled tubular glands distributed over most of the body surface. They are the most numerous sweat glands in humans and play a central role in thermoregulation by producing a watery secretion that evaporates from the skin surface and removes heat from the body.
Unlike apocrine glands, eccrine glands are generally not associated with hair follicles. Their ducts pass through the dermis and epidermis and open directly onto the skin surface through small openings commonly called sweat pores.
Each eccrine gland consists of a deep secretory portion and a duct. The secretory coil contains clear cells, dark cells, and myoepithelial cells, while the duct modifies the primary secretion by reabsorbing electrolytes before sweat reaches the surface.
Classification
Eccrine sweat glands are classified as simple coiled tubular glands. The glandular tube is highly coiled at its secretory end and becomes a duct as it travels toward the epidermal surface.
Distribution
Eccrine glands are widely distributed throughout the skin and number in the millions. Their density varies substantially among anatomical regions.
They are especially numerous on the palms, soles, and forehead.
Regional Distribution
| Region | Relative Eccrine Gland Density |
|---|---|
| Palms | Very high |
| Soles | Very high |
| Forehead | High |
| Trunk | Present |
| Limbs | Present |
| Most body surfaces | Present in varying densities |
Position Within the Skin
The secretory portion of an eccrine gland is typically located in the deep dermis or superficial hypodermis. From there, the duct ascends through the dermis and epidermis to reach the skin surface.
Basic Structure
An eccrine gland has two principal anatomical components:
- Secretory portion, which produces the primary fluid
- Duct, which transports and modifies the secretion
Secretory Portion
The secretory portion forms a tightly coiled tube. Its lumen is relatively small compared with that of an apocrine gland.
The secretory epithelium contains two principal secretory cell populations, clear cells and dark cells, together with surrounding myoepithelial cells.
Clear Cells
Clear cells are involved particularly in the production of the watery and electrolyte components of eccrine sweat. They have features associated with active ion and fluid transport.
Dark Cells
Dark cells contain numerous secretory granules and contribute glycoprotein-rich material to the glandular secretion.
They appear more intensely stained than clear cells in routine histological preparations.
Myoepithelial Cells
Myoepithelial cells lie between the secretory epithelial cells and their basement membrane. These contractile cells help support the secretory tubule and facilitate movement of secretory fluid toward the duct.
Cells of the Secretory Coil
| Cell Type | Main Feature or Function |
|---|---|
| Clear cells | Participate in fluid and electrolyte secretion |
| Dark cells | Produce glycoprotein-containing secretory material |
| Myoepithelial cells | Contract around the secretory portion and support secretion |
Eccrine Duct
The eccrine duct carries sweat from the secretory coil toward the skin surface. It is generally lined by stratified cuboidal epithelium in its dermal portion.
The duct is not simply a passive conduit. It modifies the composition of the primary secretion through electrolyte reabsorption.
Dermal Duct
Within the dermis, the duct is relatively straight compared with the secretory coil and is lined by two layers of cuboidal epithelial cells.
These cells participate in reabsorption of sodium and chloride from the primary sweat.
Intraepidermal Duct
As the duct enters the epidermis, it follows a characteristic spiral course toward the surface. This intraepidermal segment is known as the acrosyringium.
Acrosyringium
The acrosyringium is the terminal intraepidermal portion of the eccrine sweat duct. It winds through the epidermis and ultimately opens at the skin surface.
Sweat Pore
The external opening of the eccrine duct is commonly referred to as a sweat pore. Sweat released through these openings spreads over the epidermal surface and can evaporate.
Secretory Portion Versus Duct
| Feature | Secretory Portion | Duct |
|---|---|---|
| Location | Deep dermis or superficial hypodermis | Extends from gland to epidermal surface |
| Configuration | Highly coiled | Less coiled in dermis, spiral in epidermis |
| Main cells | Clear, dark, and myoepithelial cells | Stratified cuboidal epithelial cells in dermal segment |
| Main function | Produces primary secretion | Conducts and modifies sweat |
| Lumen | Relatively wider than duct lumen | Relatively narrow |
Sweat Formation
Eccrine sweat formation begins with production of a relatively isotonic primary fluid by the secretory portion of the gland. This fluid contains water and electrolytes, particularly sodium and chloride.
As the fluid travels through the duct, sodium and chloride are reabsorbed. Because the duct has relatively low permeability to water, the final sweat reaching the surface is usually hypotonic relative to plasma.
Electrolyte Reabsorption
Ductal epithelial cells recover a substantial portion of the sodium and chloride present in the primary secretion. This limits electrolyte loss during sweating.
The degree of reabsorption varies with sweat flow rate and physiological adaptation.
Sweat Composition
Eccrine sweat consists predominantly of water and contains electrolytes and small quantities of metabolic substances.
Major Components of Eccrine Sweat
| Component | General Significance |
|---|---|
| Water | Provides the fluid required for evaporative cooling |
| Sodium | Major electrolyte, partly reabsorbed in the duct |
| Chloride | Major accompanying electrolyte |
| Potassium | Present in smaller quantities |
| Lactate and other metabolites | Present in variable concentrations |
Thermoregulation
The major physiological role of eccrine glands is evaporative cooling. When body temperature rises, eccrine secretion increases and sweat spreads across the skin surface.
Evaporation requires energy. Heat is therefore transferred from the body to the water as it changes from liquid to vapor, helping reduce body temperature.
Evaporative Cooling
Sweating cools the body effectively only when sweat can evaporate. Sweat that drips from the skin without evaporating provides substantially less cooling.
Environmental humidity, air movement, clothing, and skin exposure therefore influence the effectiveness of eccrine sweating.
Control of Sweating
Thermoregulatory sweating is controlled through the nervous system, particularly pathways involving the hypothalamus and sympathetic autonomic outflow.
Temperature-sensitive mechanisms integrate information about core and skin temperature and adjust sweat production accordingly.
Sympathetic Innervation
Eccrine sweat glands are innervated by sympathetic postganglionic fibers. Unusually for the sympathetic nervous system, the principal neurotransmitter acting on thermoregulatory eccrine glands is acetylcholine.
Cholinergic Sympathetic Fibers
This sympathetic cholinergic innervation is an important physiological characteristic of eccrine glands. Acetylcholine acts on muscarinic receptors to stimulate sweat secretion.
Thermoregulatory Pathway
| Step | Event |
|---|---|
| 1 | Body or skin temperature rises |
| 2 | Thermoregulatory centers increase sympathetic output |
| 3 | Cholinergic sympathetic fibers stimulate eccrine glands |
| 4 | Sweat reaches the skin surface |
| 5 | Evaporation removes heat |
Emotional Sweating
Eccrine glands also participate in emotional sweating. Anxiety, fear, pain, and other emotional stimuli can increase sweating, particularly on the palms, soles, forehead, and axillae.
This response can occur independently of a major increase in body temperature.
Palmar and Plantar Sweating
The palms and soles contain particularly high densities of eccrine glands. Sweating in these regions can respond strongly to emotional and sensory stimuli.
Small amounts of moisture may also influence friction and grip between the skin and contacting surfaces.
Exercise
During exercise, metabolic heat production increases. Eccrine sweat secretion rises to facilitate heat dissipation and protect against excessive elevation of core body temperature.
Heat Acclimatization
Repeated exposure to hot environments can produce physiological adaptation. With heat acclimatization, sweating can begin earlier and become more effective, while sweat may contain less sodium because of enhanced ductal electrolyte conservation.
Aldosterone and Sweat
Aldosterone can enhance sodium conservation by sweat ducts during acclimatization to heat. This helps reduce salt loss during prolonged sweating.
Eccrine Versus Apocrine Glands
| Feature | Eccrine Gland | Apocrine Gland |
|---|---|---|
| Distribution | Most of body surface | Restricted regions |
| Opening | Directly onto skin surface | Usually into hair follicle |
| Secretory lumen | Relatively small | Large |
| Secretion | Watery | More viscous |
| Primary function | Thermoregulation | Regional secretion |
| Hair association | Generally absent | Usually present |
| Functional onset | Active well before puberty | Becomes prominent around puberty |
Eccrine Versus Sebaceous Glands
| Feature | Eccrine Gland | Sebaceous Gland |
|---|---|---|
| Gland type | Simple coiled tubular | Branched acinar or alveolar |
| Product | Watery sweat | Sebum |
| Typical opening | Skin surface | Hair follicle |
| Main function | Evaporative cooling | Lubrication of skin and hair |
| Secretory mechanism | Exocytotic secretion | Holocrine secretion |
Histological Appearance
In histological sections, an eccrine gland appears as multiple profiles of a coiled tubular structure in the deep dermis or hypodermis. Secretory and ductal portions can often be distinguished by their epithelial appearance and lumen size.
Identifying the Secretory Coil
The secretory portion generally has a larger lumen and paler appearance than the duct. Clear and dark secretory cells may be distinguishable in well-preserved preparations.
Identifying the Duct
The duct usually has a smaller lumen and darker staining epithelium. In the dermis, its stratified cuboidal lining commonly appears as two layers of relatively dark cells.
Histological Comparison
| Feature | Secretory Coil | Dermal Duct |
|---|---|---|
| Staining | Generally paler | Generally darker |
| Lumen | Relatively larger | Smaller |
| Cell populations | Clear, dark, and myoepithelial cells | Stratified cuboidal cells |
| Primary function | Secretion | Transport and electrolyte reabsorption |
Development
Eccrine glands develop from downgrowths of the epidermis into the underlying dermis. The deeper end differentiates into the secretory portion, while the connecting epithelial strand develops into the duct.
Unlike typical apocrine and sebaceous glands, eccrine glands develop independently of hair follicles.
Role in the Skin Barrier Environment
Eccrine secretion contributes water, electrolytes, and other substances to the skin surface. Along with sebaceous secretions and epidermal products, sweat contributes to the chemical environment of the skin.
Acidic Skin Surface
The skin surface is mildly acidic. Components of sweat, sebum, and epidermal metabolism contribute to this environment, which influences barrier function and microbial ecology.
Hyperhidrosis
Hyperhidrosis is excessive sweating beyond that required for normal thermoregulation. It may be focal or generalized.
Primary focal hyperhidrosis commonly affects the palms, soles, axillae, or face and reflects excessive activation of otherwise structurally normal sweat glands.
Common Sites of Focal Hyperhidrosis
| Site | Clinical Pattern |
|---|---|
| Palms | Palmar hyperhidrosis |
| Soles | Plantar hyperhidrosis |
| Axillae | Axillary hyperhidrosis |
| Face or scalp | Craniofacial hyperhidrosis |
Anhidrosis
Anhidrosis is an inability or marked reduction in the ability to sweat. It can result from disorders affecting sweat glands, peripheral nerves, autonomic pathways, or systemic physiology.
Extensive anhidrosis can impair heat dissipation and increase the risk of dangerous hyperthermia.
Hypohidrosis
Hypohidrosis refers to reduced sweat production. Its clinical significance depends on the extent of affected skin and environmental conditions.
Heat Illness
Effective eccrine sweating is essential during heat exposure and strenuous exercise. When heat production or environmental heat exceeds the body's capacity for cooling, core temperature can rise substantially.
Impaired sweating increases vulnerability to heat-related illness.
Cystic Fibrosis
Eccrine sweat glands have major clinical relevance in cystic fibrosis. Abnormal CFTR-mediated chloride transport in sweat ducts reduces chloride reabsorption and secondarily reduces sodium reabsorption.
As a result, sweat contains abnormally high concentrations of chloride, forming the basis of the clinical sweat chloride test.
Sweat Chloride Test
The sweat chloride test measures chloride concentration in sweat and is an important diagnostic test for cystic fibrosis when interpreted within appropriate clinical and laboratory guidelines.
Miliaria
Miliaria results from obstruction of eccrine sweat ducts. Retained sweat escapes into surrounding tissue at different levels depending on the site of ductal obstruction.
Types of Miliaria
| Type | General Level of Sweat Leakage or Obstruction |
|---|---|
| Miliaria crystallina | Very superficial epidermis |
| Miliaria rubra | Deeper epidermal duct |
| Miliaria profunda | Deeper level near or below the dermal-epidermal junction |
Eccrine Hidrocystoma
An eccrine hidrocystoma is a benign cystic lesion historically associated with sweat duct structures. Classification of sweat gland cystic lesions can be complex because some lesions show overlapping eccrine and apocrine features.
Eccrine Tumors
Numerous benign and malignant cutaneous adnexal tumors can show eccrine differentiation. Diagnosis relies on histological architecture, cytology, immunophenotype, and clinical context.
Functions of Eccrine Glands
| Function | Role |
|---|---|
| Thermoregulation | Produces sweat for evaporative heat loss |
| Electrolyte conservation | Ducts reabsorb sodium and chloride |
| Emotional sweating | Responds to emotional and autonomic stimuli |
| Palmar and plantar moisture | Contributes to local skin moisture and friction |
| Skin surface environment | Adds water, electrolytes, and metabolites to the cutaneous surface |
Key Features of Eccrine Glands
| Feature | Key Point |
|---|---|
| Gland type | Simple coiled tubular gland |
| Distribution | Most of the body surface |
| High-density regions | Palms, soles, and forehead |
| Secretory location | Deep dermis or superficial hypodermis |
| Opening | Directly onto skin surface |
| Secretory cells | Clear and dark cells |
| Contractile cells | Myoepithelial cells |
| Intraepidermal duct | Acrosyringium |
| Major function | Evaporative thermoregulation |
| Innervation | Sympathetic cholinergic |
| Final sweat | Usually hypotonic relative to plasma |
Anatomical and Functional Importance
Eccrine glands form one of the most important physiological components of the integumentary system. Their widespread distribution allows the skin to function as a large evaporative surface capable of dissipating substantial quantities of heat.
The gland is anatomically divided into a deep secretory coil and a duct. Clear and dark cells produce the primary secretion, myoepithelial cells support secretory movement, and ductal cells recover electrolytes before sweat reaches the surface.
The direct opening of eccrine ducts onto the epidermis distinguishes them from apocrine glands, while their sympathetic cholinergic innervation provides rapid neural control of sweat production during heat exposure and emotional stimulation.
Eccrine glands therefore connect skin anatomy, autonomic physiology, fluid and electrolyte transport, thermoregulation, and clinical disorders of sweating.
Published on October 15, 2026
Last updated on October 15, 2026
Last updated on October 15, 2026