Which of the following is true of both prolactin and oxytocin? Both

Correct Answer: A

Rationale: The correct answer is A: are concerned with lactation. Both prolactin and oxytocin are hormones involved in lactation. Prolactin promotes milk production in the mammary glands, while oxytocin stimulates the release of milk from the breasts during breastfeeding. Therefore, both hormones play crucial roles in the lactation process. Choice B is incorrect because oxytocin is secreted by the posterior pituitary gland, not the adenohypophysis. Choice C is incorrect because oxytocin specifically stimulates the contraction of the muscles around the mammary glands to release milk, not the production of milk. Choice D is incorrect because oxytocin is also involved in milk ejection, not just lactation itself.

Correct Answer: B

Rationale: The correct answer is B: Pineal gland. The pineal gland produces melatonin, a hormone that regulates the body's circadian rhythm, including sleep-wake cycles. This gland is sensitive to light and darkness, influencing the body's internal clock. A: Thymus gland is responsible for immune function, not circadian rhythm. C: Parathyroid gland regulates calcium levels in the body, not circadian rhythm. D: Pituitary gland controls various other hormones but not specifically circadian rhythm.

Correct Answer: B

Rationale: The correct answer is B: Islets of Langerhans. These are clusters of cells in the pancreas responsible for producing hormones like insulin and glucagon. The islets regulate blood sugar levels. Nodules (A) are not specific to the pancreas. Pancreatic medulla (C) and pancreatic cortex (D) do not refer to the specific clusters of cells in the pancreas that produce hormones.

Correct Answer: B

Rationale: The correct answer is B: adrenal glands. The adrenal glands are located on top of the kidneys and secrete hormones like cortisol and adrenaline, which play a key role in regulating metabolism and responding to stress. The pancreas (A) primarily regulates blood sugar levels. The thyroid gland (C) regulates metabolism and growth. The pituitary gland (D) controls several other endocrine glands but is not located on top of the kidneys and does not secrete metabolic stabilizers and stress regulators.

Correct Answer: C

Rationale: The correct answer is C: Glucagon promotes the breakdown of glycogen in the liver. Glucagon is secreted by the alpha cells in the islets of Langerhans in response to low blood glucose levels. When released, glucagon stimulates the liver to break down glycogen into glucose through a process called glycogenolysis, thus increasing blood glucose levels. This helps maintain blood glucose homeostasis during fasting or low glucose conditions. Options A and B are incorrect because glucagon is secreted by alpha cells, not beta cells, and in response to low blood glucose, not high. Option D is incorrect as glucagon promotes glycogen breakdown, not synthesis.