Thyroxine:

Correct Answer: D

Rationale: The correct answer is D. Thyroxine is deiodinated in the liver to T3, so approximately 33% of thyroxine is converted to the more active form, triiodothyronine. This conversion is important for regulating metabolic processes in the body. Choices A and C are incorrect because thyroxine is primarily bound to thyroxine-binding globulin in the plasma, not albumin, and it does not stimulate TSH release. Choice B is incorrect because T3 is actually more potent than thyroxine, not the other way around.

Correct Answer: B

Rationale: The correct answer is B: goiter. An enlargement of the thyroid gland is specifically referred to as a goiter. This condition can be caused by iodine deficiency or other factors affecting thyroid hormone production. Acromegaly (A) is a disorder caused by excessive growth hormone, unrelated to the thyroid. Parathyroidism (C) refers to issues with the parathyroid glands, not the thyroid. Cushing's disease (D) is a condition involving excessive cortisol production, not thyroid enlargement. Therefore, the correct term for an enlarged thyroid gland is goiter.

Correct Answer: B

Rationale: The correct answer is B, antidiuretic hormone (ADH). ADH regulates the body's fluid balance by controlling the amount of water reabsorbed by the kidneys. This helps maintain proper hydration levels and electrolyte balance. Adrenocorticotropic hormone (A) regulates cortisol production, not fluid balance. Luteinizing hormone (C) plays a role in reproductive functions, not fluid balance. Option D is incorrect because only antidiuretic hormone is directly involved in regulating fluid and electrolyte balance.

Correct Answer: C

Rationale: The correct answer is C: Acid. The stomach produces hydrochloric acid to aid in digestion by creating an acidic environment that helps break down food and kill bacteria. Alkali (A) would not aid digestion as it neutralizes acids. Trypsin (B) and Amylase (D) are enzymes produced in the pancreas, not the stomach, and play a role in digesting proteins and carbohydrates, respectively. Thus, they are not the products of the stomach for aiding digestion.

Correct Answer: A

Rationale: The correct answer is A because hormones and neurotransmitters are both chemical messengers that can sometimes be chemically identical and produce molecules that act on receptors in target cells. This is correct as both hormones and neurotransmitters are signaling molecules that carry messages between cells. Choice B is incorrect because hormones typically travel through the bloodstream to reach target tissues, while neurotransmitters travel across the synaptic cleft to transmit signals between neurons. Choice C is incorrect because hormones also act on receptors in target cells, not just neurotransmitters. Both hormones and neurotransmitters can act on specific receptors to elicit a cellular response. Choice D is incorrect because neurotransmitters primarily travel through the synaptic cleft to reach the target cell, while hormones travel through the bloodstream to reach their target tissues.