The cell of......secrete milk.

Answer

**Step-by-Step Text Solution:**

1. **Identify the Context**: The question asks about which cells secrete milk. This is related to mammalian biology, specifically the function of mammary glands.

2. **Understand Mammary Glands**: In mammals, milk is produced by mammary glands. Each mammary gland consists of several lobes.

3. **Structure of Mammary Glands**: Each mammary gland has approximately 15 to 20 lobes. These lobes are further divided into smaller structures called alveoli.

4. **Function of Alveoli**: The alveoli are the functional units of the mammary glands. The cells lining the alveoli are responsible for the secretion of milk.

5. **Hormonal Regulation**: The secretion of milk is regulated by hormones. Prolactin, secreted by the anterior pituitary gland, stimulates the production of milk in the alveoli.

6. **Milk Ejection**: The ejection of milk from the mammary glands is stimulated by another hormone called oxytocin, which is released by the posterior pituitary gland during childbirth (parturition).

7. **Milk Pathway**: Once produced in the alveoli, the milk travels through the mammary tubules, into the mammary ducts, and then into the mammary ampulla before being expelled through the nipple via the openings of the lactiferous ducts.

8. **Conclusion**: Therefore, the cells that secrete milk are the epithelial cells of the alveoli in the mammary glands.

**Final Answer**: The cells of the alveoli secrete milk.

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