Mammary glands are an example of __________.

Question

BlackTom AI · Accepted Answer

Mammary glands release part of the cell’s apical cytoplasm along with secretory product, which is characteristic of apocrine secretion.

1) Relevant concepts: Exocrine glands are classified by how they release their secretions. Merocrine (eccrine) glands secrete via exocytosis without loss of cytoplasm. Apocrine glands release secretion by budding off the apical portion of the cell, losing some cytoplasm and membrane. Holocrine glands release secretion when the entire cell disintegrates and becomes part of the secretion.

2) Step-by-step reasoning:
- Identify the mechanism of milk/lipid secretion in mammary epithelium. Milk contains lipid droplets that are enveloped by cell membrane as they are released.
- Observe that during lactation the apical portion of mammary epithelial cells pinches off and is shed into the lumen with milk fat globules; this is an apocrine-mode process.
- Compare to the definitions: the budding/pinching of apical cytoplasm matches apocrine secretion, not merocrine (which would use pure exocytosis with no cytoplasm loss) and not holocrine (which would require complete cell rupture).

3) Intermediate details: Milk fat droplets form in the cytoplasm, migrate to the apical surface, and become coated by a portion of the plasma membrane as they are released. That membrane-coated droplet is evidence of apical pinching (apocrine) rather than simple vesicular exocytosis.

4) Why the correct answer is correct: Because mammary secretion involves loss of apical cytoplasm and membrane encapsulation of lipid droplets (apical budding), it fits the apocrine mechanism. Classic histology texts classify the mammary gland as a modified apocrine gland.

5) Why other options are incorrect:
- Merocrine glands: Secrete by exocytosis without cytoplasm loss (e.g., pancreatic acinar cells, most sweat glands) — not the primary mode for milk lipid release.
- Holocrine glands: Secrete by cell disintegration (e.g., sebaceous glands) — mammary cells do not die to release milk.

6) Conclusion: Therefore, mammary glands are best classified as apocrine glands. This confirms the provided answer: Apocrine glands.

Mammary glands are an example of __________.单项选择题

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