Types of secretory cells, classification of galnds

Introduction

Glands are made from specialised epithelial cells, which are able to produce and release different kinds of secretions. These secretions can be watery, protein-rich, mucous, or even hormones.

Types of Secretory Cells

1. Serous cells

• They produce a thin and watery secretion that contains many proteins, usually enzymes.
• Their cytoplasm stains darker in H&E staining because it has a lot of rough ER and also many secretory granules.
• The nucleus is round and placed in the basal part of the cell.
• We can find them for example in pancreas and parotid gland.
• Under microscope they look quite “packed” because they have many organelles for protein synthesis.

2. Mucous cells

• These cells secrete mucin, which becomes mucus when it absorbs water.
• The cytoplasm usually looks pale or even empty in H&E, because mucin is not staining very well.
• The nucleus is flattened and pushed to the basal side.
• hey are common in salivary glands and in epithelium of respiratory and gastrointestinal tract.

3. Mixed (seromucous) cells

• Some glands contain both serous and mucous secretory parts.
• A typical feature is the serous demilune, which is a small half-moon shaped cap of serous cells on mucous acini.
• We can see this structure in mixed salivary glands like submandibular gland.

4. Myoepithelial cells

• These cells do not produce secretion themselves, but they help to push the secretion out of the gland.
• They are located between the basal lamina and the secretory cells.
• Because they contain actin and myosin, they are able to contract.
• They are important in salivary, sweat, and also mammary glands.

Classification of Glands

1. According to where secretion goes

Exocrine glands

• They release their product onto an epithelial surface using a duct.

Examples: salivary glands, sweat glands, gastric glands.

Endocrine glands

• They have no ducts, and they release hormones directly into blood or surrounding tissue fluid.

Examples: thyroid, adrenal, pituitary.

Paracrine and autocrine secretion

• Paracrine secretion affects nearby cells.
• Autocrine secretion affects the same cell that produced the substance. These types are common in tissues with hormone-like signalling.

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2. According to mode of secretion

Merocrine (eccrine)

• The secretory product is released by exocytosis.
• This is the most common mechanism; the cell stays intact.

Examples: exocrine pancreas, most sweat glands.

Apocrine

• A small part of the apex of the cell is pinched off together with the secretion.

Seen in mammary gland and apocrine sweat glands (like in axilla).

Holocrine

The whole cell disintegrates and becomes a part of the secretion.

Example: sebaceous glands

Since the whole cell is lost, these glands need continuous cell replacement.

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3. According to number of cells

Unicellular glands

Made from only one cell.

Example: goblet cells in respiratory or intestinal epithelium.

Multicellular glands

Made from many secretory cells forming secretory units and ducts.

Most exocrine glands belong to this group.

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4. According to shape of secretory portion

Tubular

Secretory units have a tube-like shape.

Example: intestinal glands.

Acinar (alveolar)

Secretory units are round or sac-like, similar to small berries.

Example: parotid gland, exocrine pancreas.

Tubuloacinar

Combination of tubular and acinar structures.

Seen in many mixed salivary glands.

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5. According to duct system

Simple glands

Duct is not branched.

They can be simple tubular, simple coiled, or simple branched.

Compound glands

Duct system is branched and more complex.

Examples: pancreas, major salivary glands.

They often have lobules separated by connective tissue.

Examples of Glands and Their Cell Types

• Pancreas – mainly serous acini (merocrine) plus endocrine islets that release hormones.
• Goblet cells – unicellular mucous-secreting cells.
• Sebaceous gland – holocrine secretion where whole cells are lost.
• Mammary gland – partly apocrine secretion of lipids.
• Submandibular gland – mixed gland: mostly serous but also mucous units with demilunes.

Citation

Morphologia, E. O. O. J. (2019). Junqueira’s Basic Histology : Text & Atlas (15th ed.), 2018. Morphologia, 13(2), 101–104. https://doi.org/10.26641/1997-9665.2019.3.101-104

slides from Ph.D. Lucia Fraser Lantová