This cone-shaped gland is located in the head and is called the “biological clock.”

Correct Answer: C

Rationale: The correct answer is C: Pineal gland. The pineal gland is located in the brain and is often referred to as the "biological clock" due to its role in regulating the sleep-wake cycle through the secretion of melatonin. The posterior pituitary (choice A) is responsible for releasing hormones produced by the hypothalamus, not related to the circadian rhythm. The hypothalamus (choice B) is involved in regulating various physiological processes but is not directly associated with the circadian rhythm. The thymus (choice D) plays a role in the immune system, not in regulating the biological clock. Thus, the pineal gland is the correct answer as it specifically controls the circadian rhythm.

Correct Answer: A

Rationale: The correct answer is A: sweat gland. Endocrine glands secrete hormones directly into the bloodstream, affecting distant target organs. Sweat glands, on the other hand, are exocrine glands that release sweat onto the skin surface to regulate body temperature. The adrenal glands, thyroid gland, and pituitary gland are all endocrine glands that secrete hormones, making them the correct choices. A sweat gland does not secrete hormones into the bloodstream, so it does not qualify as an endocrine gland.

Correct Answer: C

Rationale: Rationale: 1. Oxytocin is released during childbirth to stimulate uterine contractions. 2. As contractions increase, oxytocin secretion is further stimulated in a positive feedback loop. 3. This positive feedback mechanism amplifies the contractions until delivery. 4. Calcitonin regulates calcium levels, histamine is involved in allergic responses, and melatonin regulates sleep-wake cycles. Summary: - Calcitonin, histamine, and melatonin do not exhibit positive feedback regulation like oxytocin during childbirth.

Correct Answer: B

Rationale: The correct answer is B: Adrenal gland. The adrenal gland is located just superior to the kidneys. It is part of the endocrine system and plays a crucial role in producing hormones such as cortisol and adrenaline. The pituitary gland (A) is located in the brain, the pancreas (C) is situated in the abdomen, and the ovaries (D) are found in the pelvic region. The adrenal gland's location and function make it the most appropriate choice in this scenario.

Correct Answer: C

Rationale: The correct answer is C: Acromegaly. Hypersecretion of growth hormone in adults leads to acromegaly, characterized by enlarged hands, feet, and facial features. This occurs due to excess GH after epiphyseal plate closure. A: Cretinism is caused by congenital hypothyroidism, not GH hypersecretion. B: Myxoedema is a severe form of hypothyroidism, not related to GH. D: Graves disease is an autoimmune disorder causing hyperthyroidism, not GH hypersecretion.