Calcitonin is a hormone of which of following:

Correct Answer: B

Rationale: Calcitonin is a hormone produced by the thyroid gland. It helps regulate calcium levels in the body by inhibiting bone breakdown and lowering blood calcium levels. The thyroid gland is responsible for producing various hormones, including calcitonin. Adrenal cortex (A) produces hormones like cortisol, Pituitary gland (C) produces hormones like growth hormone, and Thymus gland (D) is involved in immune function, not hormone regulation. Therefore, the correct answer is B (Thyroid gland).

Correct Answer: A

Rationale: The correct answer is A: Epinephrine & norepinephrine. These hormones are responsible for the fight-or-flight response. When facing a threat, the adrenal glands release these hormones, which increase heart rate, blood pressure, and energy levels to prepare the body to either fight or flee. Epinephrine and norepinephrine are part of the sympathetic nervous system's response to stress. Choices B, C, and D are incorrect: B: Insulin & glucagon regulate blood sugar levels, not the fight-or-flight response. C: Estrogen & progesterone are reproductive hormones, not involved in the fight-or-flight response. D: Thyroxin & melatonin regulate metabolism and sleep-wake cycles, respectively, not the fight-or-flight response.

Correct Answer: B

Rationale: The correct answer is B: Hormones. The endocrine system consists of ductless glands that secrete hormones directly into the bloodstream to regulate various bodily functions. Hormones are chemical messengers that help control metabolism, growth, development, mood, and other physiological processes. Enzymes (choice A) are not secreted by the endocrine system but by exocrine glands. Electrolytes (choice C) are ions essential for various bodily functions but are not directly secreted by glands of the endocrine system. Choice D, chemicals, is too broad and vague as all substances can be considered chemicals.

Correct Answer: B

Rationale: The correct answer is B. In hyperthyroidism, the thyroid gland produces an excess of thyroid hormones T3 and T4, leading to negative feedback on the pituitary gland, resulting in decreased TSH levels. Therefore, you would expect decreased TSH and increased T3, T4 levels. A is incorrect because TSH would be decreased, not increased. C is incorrect because TSH would be decreased in hyperthyroidism. D is incorrect because T3 and T4 would be increased in hyperthyroidism.

Correct Answer: A

Rationale: The correct answer is A: negative feedback mechanisms. Negative feedback mechanisms help maintain hormone levels within a narrow range by inhibiting further hormone production once a certain level is reached. When hormone levels rise, negative feedback signals the body to decrease hormone production, preventing excessive levels. Positive feedback mechanisms, on the other hand, amplify hormone production. Hormone-receptor complexes and hormone-gene complexes are not directly responsible for maintaining hormone levels within a narrow range but rather play roles in hormone signaling and gene expression, respectively.