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Merocrine – Definition and Function

Merocrine describes a secretion type in which gland cells release their contents without any cell damage. It is the most common secretion method in the human body.

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Things worth knowing about "Merocrine"

Merocrine describes a secretion type in which gland cells release their contents without any cell damage. It is the most common secretion method in the human body.

What does merocrine mean?

Merocrine (also: merocrine secretion) describes a secretion mechanism in which gland cells release their products – such as enzymes, hormones, or sweat – via exocytosis, without sustaining any structural damage or losing cell material. The cell remains fully intact and functional after secretion.

Classification: Types of secretion compared

In histology and cell biology, three fundamental types of secretion are distinguished:

Merocrine (eccrine): Secretion via exocytosis; the cell remains unharmed. Examples: salivary glands, eccrine sweat glands, pancreas.
Apocrine: The apical portion of the cytoplasm is shed along with the secretory product, resulting in partial cell loss. Examples: apocrine sweat glands, mammary glands.
Holocrine: The entire cell becomes the secretory product – the cell dies in the process. Example: sebaceous glands of the skin.

Mechanism of merocrine secretion

In merocrine secretion, the substances to be secreted are first synthesized in the endoplasmic reticulum and then packaged in the Golgi apparatus. The resulting secretory granules (membrane-bound vesicles) migrate to the cell surface, where they fuse with the plasma membrane and discharge their contents into the extracellular space or into a glandular duct system. This process is called exocytosis. The cell membrane is preserved and can be replenished.

Occurrence and clinical relevance

Merocrine secretion is the most widespread secretion type in the body, occurring in numerous organs and glands:

Eccrine sweat glands: Production of sweat for thermoregulation and skin hydration.
Salivary glands: Release of salivary enzymes such as amylase for digestion.
Pancreas: Release of digestive enzymes (e.g., lipase, proteases) and hormones (e.g., insulin, glucagon).
Small intestinal glands (crypts of Lieberkuhn): Secretion of digestive juices.
Endocrine glands: Hormone secretion into the bloodstream, e.g., in the thyroid gland or adrenal gland.

Distinction: Eccrine vs. merocrine

In scientific literature, the terms merocrine and eccrine are often used interchangeably, especially when referring to eccrine sweat glands. Strictly speaking, eccrine refers exclusively to eccrine sweat glands, while merocrine is the broader histological term for this type of secretion, applicable to all glands that use this mechanism.

Relevance in medicine

Understanding merocrine secretion is fundamental to many medical specialties, including gastroenterology, endocrinology, and dermatology. Disruptions in exocytosis or vesicle formation can lead to disease, for example reduced insulin secretion in type 2 diabetes mellitus or impaired function of the exocrine pancreas (exocrine pancreatic insufficiency).

References

Lüllmann-Rauch, R. & Asan, E. – Taschenlehrbuch Histologie, 6th edition. Thieme Verlag, 2019.
Junqueira, L. C. & Carneiro, J. – Basic Histology: Text and Atlas, 12th edition. McGraw-Hill Medical, 2010.
Alberts, B. et al. – Molecular Biology of the Cell, 7th edition. W. W. Norton & Company, 2022.

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