Endocrine system consists of ductless glands which secrete:

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: 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.

Correct Answer: B

Rationale: The correct answer is B: IGF. Increased growth of skeletal and soft tissue, along with other symptoms, suggest acromegaly due to excess growth hormone (GH) secretion. GH stimulates the liver to produce insulin-like growth factor (IGF), which mediates many of GH's effects. In acromegaly, elevated IGF levels contribute to the clinical manifestations. Option A (GH) is incorrect because GH levels may be high but not necessarily in response to oral glucose. Option C (GH and IGF) is incorrect as GH alone does not directly increase in response to oral glucose. Option D (ADH) is unrelated to the scenario described.

Correct Answer: C

Rationale: Plasma osmolality is primarily regulated by the concentration of solutes in the blood. Vasopressin, also known as antidiuretic hormone (ADH), plays a key role in regulating water reabsorption in the kidneys, thus affecting plasma osmolality. When plasma osmolality increases, vasopressin is released to increase water reabsorption, leading to a decrease in plasma osmolality. Progesterone, cortisol, and aldosterone do not directly influence water reabsorption and therefore do not have as significant an impact on plasma osmolality as vasopressin.

Correct Answer: D

Rationale: The correct answer is D because steroid hormones bind to a receptor inside the target cell, are made from cholesterol, and cause the cell to make new proteins. This is known as the mechanism of steroid hormone action. Choice A is correct as steroid hormones need to bind to intracellular receptors to exert their effects. Choice B is also correct as steroid hormones are derived from cholesterol. Choice C is correct as one of the main actions of steroid hormones is to regulate gene expression and induce the synthesis of new proteins within the cell. Therefore, all of these statements are true regarding steroid hormones, making choice D the correct answer.