The growth hormone produced by the pituitary gland is known as _______.

Correct Answer: A

Rationale: The correct answer is A: somatotropin. The growth hormone produced by the pituitary gland is known as somatotropin. - "Somato" refers to the body, indicating its role in regulating body growth. - "Tropin" refers to stimulation, emphasizing its function in promoting cell growth and regeneration. - Prolactin (B) is responsible for milk production. - Luteinizing hormone (C) and follicle-stimulating hormone (D) are involved in reproductive functions, not growth regulation.

Correct Answer: D

Rationale: The correct answer is D because growth hormone promotes long bone growth during the formative years by stimulating the growth plates in bones. This hormone plays a crucial role in skeletal growth and development. Choice A is incorrect because somatostatin is a different hormone that inhibits growth hormone release. Choice B is incorrect because growth hormone is primarily regulated by neural mechanisms. Choice C is incorrect because growth hormone actually promotes muscle growth and reduces fat mass.

Correct Answer: C

Rationale: The correct answer is C: G protein acts as the link between first and second messengers. Rationale: 1. Peptide hormones cannot enter the cell membrane due to their large size. 2. Hormones do not directly stimulate genes; they act through signaling pathways. 3. G proteins are key in transmitting signals from hormone receptors to second messengers, facilitating cellular responses. 4. The hormone receptor complex typically stays on the cell membrane to initiate signaling cascades.

Correct Answer: A

Rationale: The correct answer is A because cellular responses to hormones initiating second-messenger systems can activate various pathways. Different hormones can utilize different second messengers such as cAMP, cGMP, IP3, and DAG. This diversity allows for a wide range of responses in target cells. Choice B is incorrect because cyclic AMP phosphodiesterase degrades cAMP, not forms an active second messenger. Choice C is incorrect as it describes the mechanism of a specific protein kinase, which is not a characteristic of second-messenger systems. Choice D is incorrect since hormone binding to intracellular receptors typically leads to gene transcription regulation, not direct activation of second-messenger systems.

Correct Answer: B

Rationale: The correct answer is B: Calcium. Calcium ions are commonly used as second messengers for amino acid-base hormones due to their ability to trigger various cellular responses. When the hormone binds to its receptor on the cell surface, it activates specific signaling pathways that lead to an increase in intracellular calcium levels. This rise in calcium ions then initiates downstream signaling cascades, ultimately regulating processes such as gene expression, cell growth, and metabolism. Choice A - Iron: Iron is not typically involved in signaling pathways for amino acid-base hormones. It is more commonly known for its role in oxygen transport and storage in hemoglobin. Choice C - Sodium: While sodium ions play essential roles in cellular functions, they are not typically utilized as second messengers for amino acid-base hormones. Sodium is more commonly associated with maintaining cell membrane potential and fluid balance. Choice D - Chlorine: Chlorine ions are not typically involved in signaling pathways for amino acid-base hormones. Chlorine is primarily known for its role in maintaining