Most endocrine organs are prodded into action by other hormones; this type of stimulus is called:

Correct Answer: A

Rationale: The correct answer is A: hormonal stimulus. Endocrine organs are typically activated by other hormones circulating in the bloodstream, triggering a chain reaction of hormonal responses. This is known as hormonal stimulus. Other choices are incorrect because humoral stimulus refers to changes in blood levels of ions or nutrients, neural stimulus involves nerve impulses, and receptor-mediated stimulus is not a recognized term in endocrine physiology.

Correct Answer: D

Rationale: The correct answer is D: thymus gland. The thymus gland is crucial for the development and maturation of T cells, a type of immune cell. The hormones produced by the thymus gland, such as thymosin, play a key role in the proper functioning of the immune system. Without a functional thymus gland, the immune response would be compromised. Explanation for why other choices are incorrect: A: Adrenal medulla does not play a direct role in immune response development. B: Pancreas primarily produces hormones related to blood sugar regulation, not immune response. C: Thyroid gland produces hormones that regulate metabolism, not directly related to immune response development.

Correct Answer: C

Rationale: The correct answer is C: hypophyseal portal system. This system involves a direct blood vessel connection between the hypothalamus and the anterior pituitary gland, allowing hormones synthesized in the hypothalamus to be rapidly transported to the anterior pituitary without being diluted in the general circulation. The hepatic portal system (A) involves blood flow from the digestive system to the liver. The general circulatory system (B) would dilute the hormones before reaching the anterior pituitary. A feedback loop (D) is a mechanism that regulates hormone levels but is not the primary mode of transportation between the hypothalamus and anterior pituitary.

Correct Answer: B

Rationale: Leptin is primarily secreted by adipocytes, which are fat cells. Adipocytes play a crucial role in regulating energy balance and appetite through leptin secretion. Lymphocytes are immune cells, goblet cells secrete mucus, and fibroblasts are connective tissue cells, none of which are involved in leptin secretion.

Correct Answer: C

Rationale: The correct answer is C: hydrocortisones. Eicosanoids are signaling molecules derived from fatty acids, including prostaglandins and leukotrienes, which act as paracrines. Hydrocortisone is a steroid hormone, not an eicosanoid. It functions differently from eicosanoids, which act locally as signaling molecules. Therefore, hydrocortisones do not belong to the eicosanoid category. Choices A, B, and D are incorrect because paracrines, leukotrienes, and prostaglandins are all types of eicosanoids with specific functions in the body.