Chemical substances secreted by cells into the extracellular fluids that regulate the metabolic function of other cells in the body are called ________.

Correct Answer: D

Rationale: The correct answer is D: hormones. Hormones are chemical substances secreted by cells into extracellular fluids to regulate metabolic functions in other cells. They act as messengers, traveling through the bloodstream to target tissues. Enzymes (A) are catalysts that accelerate chemical reactions. Antibodies (B) are proteins produced by the immune system to neutralize pathogens. Proteins (C) are essential macromolecules for various cellular functions but do not specifically regulate metabolic functions in other cells like hormones do.

Correct Answer: B

Rationale: In the context of the endocrine system and second-messenger systems of hormone action, understanding the role of different molecules as second messengers is crucial. In this question, the correct answer is B) calmodulin. Calmodulin is not a second messenger itself but rather a calcium-binding protein that plays a role in transmitting the signal initiated by the second messenger. A) cyclic AMP is a classic example of a second messenger that mediates the action of various hormones like epinephrine and glucagon. It activates protein kinase A, leading to intracellular responses. C) cyclic GMP is another second messenger, particularly associated with signaling pathways involving nitric oxide. It regulates processes like smooth muscle relaxation and neurotransmission. D) Inositol triphosphate (IP3) is also a second messenger that is produced upon activation of certain receptors. IP3 triggers the release of calcium from intracellular stores, leading to various cellular responses. Educationally, this question helps reinforce the importance of understanding the specific roles of different molecules in signaling pathways within the endocrine system. It highlights the diversity of second messengers and their distinct functions in mediating cellular responses to hormonal stimuli. Students need to grasp these concepts to comprehend how hormones exert their effects on target cells and tissues.

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: B

Rationale: Step 1: Negative feedback is the primary mechanism in endocrine system regulation to maintain homeostasis. Step 2: When hormone levels reach a certain set point, negative feedback signals the gland to stop producing that hormone. Step 3: This ensures that hormone levels remain within a specific range. Step 4: Positive feedback would lead to further hormone secretion, disrupting homeostasis. Step 5: Neural feedback is not a common mechanism for regulating endocrine secretions.

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.