Correct Answer: A

Rationale: Hormones are signaling molecules produced by glands in multicellular organisms. They travel through the bloodstream to specific target cells where they regulate various physiological processes, including growth, differentiation, and metabolism. Neurons (choice B) are nerve cells that transmit nerve impulses and are not responsible for controlling growth, differentiation, or metabolism. Glands (choice C) produce and release hormones but are not the chemical messengers themselves. Second messengers (choice D) are molecules involved in intracellular signal transduction, not the primary chemical messengers controlling growth, differentiation, and metabolism. Therefore, hormones (choice A) are the correct answer as they match the description provided in the question.

Correct Answer: A

Rationale: Enlargement of the thyroid, known as a goiter, can compress the nearby structures in the neck, including the esophagus. This compression can lead to symptoms such as difficulty swallowing (dysphagia) or a sensation of pressure in the throat. Therefore, an enlarged thyroid gland is expected to affect swallowing. Choices B, C, and D are incorrect because a goiter primarily affects structures in the neck due to its physical enlargement, rather than directly impacting insulin levels, sleep, or digestion.

Correct Answer: D

Rationale: The correct answer is D because the urinary system eliminates some waste products of digestion. After digestion in the digestive system, nutrients are absorbed into the bloodstream, and waste products are transported to the kidneys via the urinary system to be excreted as urine. This process helps eliminate waste products generated during digestion, illustrating the coordination between the digestive and urinary systems. Choices A, B, and C are incorrect. Choice A is incorrect as the ureter is part of the urinary system, not controlled by the digestive system. Choice B is incorrect as the urinary system primarily removes metabolic waste, not toxins from digestion. Choice C is incorrect because the digestive system mainly aids in digestion and nutrient absorption, not hormone production affecting urination.

Correct Answer: C

Rationale: The gall bladder is part of the digestive system. Its primary function is to store and concentrate bile produced by the liver and release it into the small intestine to aid in the digestion of fats. This process facilitates the breakdown and absorption of fats from the food we consume. Choices A, B, and D are incorrect as the gall bladder is not associated with the endocrine, urinary, or nervous systems.

Correct Answer: B

Rationale: The hypothalamus is a small region of the brain that plays a crucial role in linking the nervous system to the endocrine system. It helps regulate various bodily functions by releasing hormones that signal the pituitary gland to release other hormones that control metabolism, growth, reproduction, sleep, and other important processes. Therefore, the hypothalamus is a key component of the endocrine system. Choices A, C, and D are incorrect because the hypothalamus is not part of the cardiovascular, respiratory, or lymphatic systems.