Which system works closely with the endocrine system to coordinate the body's functions?

Correct Answer: A

Rationale: The correct answer is A: nervous system. The nervous system works closely with the endocrine system to coordinate the body's functions through the release of neurotransmitters and hormones. The nervous system uses electrical signals to transmit information rapidly, while the endocrine system releases hormones into the bloodstream to regulate various bodily functions. The immune system (B) protects the body from infections, the circulatory system (C) transports nutrients and oxygen throughout the body, and the respiratory system (D) is responsible for gas exchange. However, these systems do not directly coordinate with the endocrine system in the same way the nervous system does.

Correct Answer: B

Rationale: The correct answer is B: neurons that extend from the hypothalamus to the pituitary. The hypothalamus produces hormones that are stored and released by the posterior pituitary gland. This communication is facilitated by specialized neurons that extend from the hypothalamus to the pituitary, forming the hypothalamic-pituitary axis. These neurons release hormones into the bloodstream, which then reach the posterior pituitary gland and stimulate the release of its stored hormones. Choice A is incorrect because the posterior pituitary does not directly receive messages through a capillary network. Choice C is incorrect as Schwann cells are responsible for myelinating peripheral nerves, not hormone communication. Choice D is incorrect because while the hypothalamus communicates with the pituitary gland through neurons, it does not involve a capillary network.

Correct Answer: A

Rationale: Step 1: Steroids are lipid-soluble molecules, allowing them to easily diffuse through the plasma membrane of target cells. Step 2: Once inside the cell, steroids can enter the nucleus to bind to specific receptors and regulate gene expression. Step 3: Steroids do not catalyze cyclic AMP; this function is typically associated with non-steroid hormones like adrenaline. Step 4: Therefore, the correct answer is A because steroids do not catalyze cyclic AMP, unlike other hormones.

Correct Answer: B

Rationale: The correct answer is B because the bloodstream can carry hormones throughout the body simultaneously, reaching various target cells and organs. This enables a single endocrine hormone to produce responses in multiple parts of the body. In contrast, nerve cells can only target a limited number of cells through direct connections. Choice A is incorrect because endocrine hormones can also target multiple responses, not just one. Choice C is incorrect as the endocrine system and nervous system can interact. Choice D is incorrect as endocrine hormones can have broad effects on multiple target cells.

Correct Answer: D

Rationale: In Graves disease, there is an overproduction of thyroid hormones due to autoimmune stimulation. Thyroid-stimulating hormone (TSH) is decreased because the excessive thyroid hormones suppress its production through negative feedback. A and B are incorrect because both T3 and T4 levels are elevated in Graves disease. C is incorrect as DIT is a precursor to thyroid hormones and its levels may not necessarily be decreased in Graves disease.