In mammalian physiology, which peptide hormone (protein) primarily regulates milk production (lactation) in the mammary glands?

Introduction / Context:
Reproduction and lactation are key topics in human and animal physiology. After childbirth, hormones regulate the production and secretion of milk in the mammary glands. This question asks which protein type hormone is primarily responsible for stimulating milk production in mammals.

Given Data / Assumptions:

• Milk production (lactation) occurs in mammary glands of mammals.
• The options include structural proteins and a hormone.
• We assume standard endocrine physiology for mammals.
• The hormone that stimulates milk synthesis is the focus, not the reflex of milk ejection.

Concept / Approach:
Prolactin is a peptide hormone produced by the anterior pituitary gland. It plays the central role in promoting milk synthesis in mammary gland tissue after childbirth. While oxytocin stimulates milk ejection by causing contraction of smooth muscle around alveoli, prolactin is the hormone that regulates the production of milk itself. Structural proteins like collagen, elastin, and actin perform mechanical and support roles in tissues and muscles, not hormone regulation of lactation. Therefore, the correct option is the one identifying prolactin as the hormone that regulates milk production.

Step-by-Step Solution:

Verification / Alternative check:
Physiology textbooks describe the lactation reflex in two parts: prolactin for milk synthesis and oxytocin for milk ejection. Charts showing hormonal changes during and after pregnancy show prolactin levels rising as the body prepares for breastfeeding. The mammary glands respond to prolactin by producing milk. This separation of functions confirms that prolactin is the primary regulator of milk production.

Why Other Options Are Wrong:

• Actin is wrong because it is a muscle protein involved in contraction, not a hormone.
• Elastin is wrong because it provides elasticity to tissues and does not regulate lactation.
• Collagen is wrong because it is a major structural protein of connective tissues and not an endocrine hormone.

Common Pitfalls:
Some learners confuse oxytocin and prolactin, thinking that oxytocin produces milk because it is associated with breastfeeding. It actually helps eject milk already produced. Remember the pair as follows: prolactin promotes production, oxytocin promotes outflow. Another pitfall is not noticing that the question emphasizes regulation of milk production, which points directly to prolactin as the correct answer.

Final Answer:
Prolactin, a peptide hormone secreted by the anterior pituitary