Question

Contraction of the mammary glands and ducts during the milk-ejection reflex is stimulated by a. prolactin. b. oxytocin. c. estrogen. d. progesterone.

Short answer

The contraction of the mammary glands and ducts during the milk-ejection reflex is stimulated by b. Oxytocin.

Step-by-step solution

Understand the Concept involved

The milk-ejection reflex involves contractions in the mammary glands and ducts, where milk gets accumulated and then let out or 'ejected'. Certain hormones regulate these contractions.

Link Hormones to their Functions

Know that different hormones have different functions. Prolactin (choice a) is primarily involved in the production of milk, Estrogen (choice c) regulates a wide range of processes including the menstrual cycle, and Progesterone (choice d) prepares the uterus for pregnancy. None of these directly cause the contraction of the mammary glands during the milk-ejection reflex.

Identify the Correct Hormone

Oxytocin (choice b) is the hormone that causes the contraction of the muscle cells around the milk-producing glands and ducts, leading to the ejection of milk during breastfeeding. Hence, the correct answer is b. oxytocin. So, the final answer is: The contraction of the mammary glands and ducts during the milk-ejection reflex is stimulated by b. Oxytocin.

Key concepts

Oxytocin

Oxytocin is often referred to as the 'love hormone' due to its role in promoting social bonding and maternal behaviors. In the context of breastfeeding, oxytocin serves a critical physiological function.

Oxytocin is released in response to various stimuli, such as a baby's suckling on the mother’s breast. This release triggers the milk-ejection reflex—or 'let-down'—wherein oxytocin causes the smooth muscle cells surrounding the mammary alveoli to contract. This contraction expels milk from the alveoli into the ducts, and then into the infant’s mouth.

Beyond its role in lactation, oxytocin also facilitates uterine contractions during childbirth and can influence emotional bonding between individuals. Its multi-faceted influence on human physiology is still an active area of research.

Prolactin

While oxytocin handles the ejection of milk, prolactin plays the lead role in milk production. Prolactin is a hormone released by the pituitary gland and its levels increase significantly during pregnancy.

The elevation in prolactin prepares the breasts for lactation and, after birth, maintains milk production. It works by stimulating the mammary glands to produce milk in anticipation of breastfeeding.

Interestingly, prolactin levels are not static—they rise in response to the infant's feeding patterns. During breastfeeding, more frequent suckling increases prolactin levels and thus encourages more milk production. This demonstrates a feedback mechanism that ensures a sufficient milk supply based on the infant's demand.

Mammary Gland Contraction

The action of mammary gland contraction is essential for the process of lactation. When the mammary glands contract, the milk produced in the glands is pushed through the milk ducts towards the nipple, where it can be accessed by the nursing baby.

The contraction of the mammary gland is a carefully coordinated physiological event, heavily dependent on oxytocin. It is a fantastic example of how our bodies utilize hormones to induce mechanical actions that fulfill specific biological roles—in this case, to provide nourishment to infants.

Human Physiology

The process of milk ejection elegantly illustrates the complexity and harmony of human physiology. Human physiology is the study of how our body functions, and hormones like oxytocin and prolactin are prime examples of physiological regulators—substances that govern a myriad of bodily functions.

In the scenario of lactation, we see how hormonal signals such as the release of oxytocin can command a physical response like mammary gland contraction. This complex interplay is a testament to the precision and adaptability of human physiology, which is capable of supporting the growth and development of a new life through processes like breastfeeding.