Thyroxine is a peptide hormone, but its mechanism is different from other peptide hormones. Which of the following statements is true concerning this difference?

Correct Answer: B

Rationale: The correct answer is B: Thyroxine does not require a second messenger to effect a response. Thyroxine is a non-peptide hormone derived from the amino acid tyrosine, not a peptide hormone. It acts directly on the cell by binding to nuclear receptors, which then bind to specific regions of DNA to regulate gene expression. This mechanism is different from peptide hormones, which typically require second messengers like cAMP or calcium to transmit their signal inside the cell. Therefore, choice B is correct. Choices A, C, and D are incorrect because thyroxine does not cause positive feedback, is not highly specific in cell targeting, and does not target all cells for cellular metabolism stimulation.

Correct Answer: D

Rationale: The correct answer is D: ovary. The anterior pituitary gland secretes follicle-stimulating hormone (FSH) and luteinizing hormone (LH) that regulate the function of the ovaries. FSH stimulates the growth of ovarian follicles, while LH triggers ovulation and stimulates the production of progesterone and estrogen. The pancreas (A) is mainly controlled by insulin and glucagon from the pancreas itself. The parathyroid gland (B) is regulated by parathyroid hormone (PTH) secreted by the parathyroid glands. The adrenal medulla (C) is controlled by the sympathetic nervous system, not by anterior pituitary hormones.

Correct Answer: B

Rationale: The correct answer is B because parathyroid hormone (PTH) actually increases blood calcium levels. PTH achieves this by releasing calcium from bone (A), promoting reabsorption of calcium in the kidneys (C), and activating Vitamin D for increased calcium absorption in the intestines (D). By decreasing blood calcium levels, it would go against the primary function of PTH. This choice is incorrect as PTH is known for its role in increasing blood calcium levels through the mentioned mechanisms.

Correct Answer: C

Rationale: Rationale: C is correct because insulin does not stimulate the breakdown of glycogen. Insulin promotes the storage of glucose as glycogen, not its breakdown. A, B, and D are incorrect because insulin does stimulate cellular absorption of glucose, usage of glucose for energy, and lowers blood glucose levels, respectively. Insulin's main role is to facilitate the uptake and storage of glucose, not its breakdown.

Correct Answer: A

Rationale: The correct answer is A: Diarrhoea. Hypothyroidism is associated with decreased metabolic function, leading to symptoms such as lethargy, anorexia, and weight gain. Diarrhoea is not typically a symptom of hypothyroidism; instead, it can be seen in conditions like hyperthyroidism where there is an excess of thyroid hormone. In hypothyroidism, the digestive processes slow down, which can lead to constipation rather than diarrhoea. Therefore, the effects of hypothyroidism do not include diarrhoea.