Regarding the islets of Langerhans:

Correct Answer: D

Rationale: The correct answer is D because blood from the islets of Langerhans drains into the hepatic portal vein. This is important for the regulation of blood glucose levels by allowing insulin and glucagon produced by the islets to reach the liver directly. Choice A is incorrect because D cells secrete somatostatin, not pancreatic polypeptide. Choice B is incorrect as beta cells, not A cells, are the most common in the islets. Choice C is incorrect as the islets are most plentiful in the tail of the pancreas.

Correct Answer: C

Rationale: The correct answer is C because steroid hormones are lipid-soluble and can diffuse through cell membranes. Once inside the cell, they bind to specific receptors in the cytoplasm. This hormone-receptor complex then enters the nucleus to regulate gene expression. Option A is incorrect because steroid hormone receptors are not found on nutrient molecules like glucose. Option B is incorrect as these receptors are not typically located in the interstitial fluid. Option D is also incorrect because steroid hormone receptors are not located on the cell membranes of target tissues.

Correct Answer: B

Rationale: Step-by-step rationale for why choice B (thyroid hormone) is correct: 1. Thyroid hormone is a key hormone that regulates metabolism and growth. 2. Intracellular hormone receptors are specific to certain hormones. 3. Disruption of thyroid hormone levels can lead to metabolic disorders. 4. Pesticide binding to the thyroid hormone receptor can interfere with its normal function. Summary of why other choices are incorrect: A: Melatonin regulates sleep-wake cycles, not metabolism. C: Growth hormone regulates growth and development, not metabolism. D: Insulin regulates blood sugar levels, not metabolism.

Correct Answer: A

Rationale: The correct answer is A: Closes trachea when swallowing. The epiglottis is a flap of tissue that covers the trachea (windpipe) during swallowing to prevent food or liquid from entering the airway. It ensures that food goes down the esophagus instead of the trachea. This action helps protect the respiratory system from aspiration. Choices B, C, and D are incorrect. B is incorrect because the epiglottis closes the trachea, not the esophagus, during swallowing. C is incorrect because the trachea is supported by rings of cartilage, not the epiglottis. D is incorrect because the epiglottis does not close the nasal cavity but rather the trachea.

Correct Answer: B

Rationale: The correct answer is B: Sympathetic division. This division of the autonomic nervous system is responsible for the body's "fight or flight" response during moments of danger. When an individual perceives a threat, the sympathetic division activates to prepare the body for action, including sending signals to the adrenal glands to release adrenaline and cortisol, which help increase heart rate, blood pressure, and energy levels. The other choices are incorrect because: A: The central nervous system consists of the brain and spinal cord, which are responsible for processing and transmitting information within the body, but it does not directly send signals to the adrenal glands. C: The parasympathetic division is responsible for the body's "rest and digest" functions and works in opposition to the sympathetic division. It does not send signals to the adrenal glands during moments of danger. D: The peripheral nervous system consists of nerves outside the brain and spinal cord, including sensory and motor nerves, but it does not specifically send signals