Stimulation of the mother's nipples by the baby's nursing initiates sensory impulses which pass into the central nervous system and eventually reach the hypothalamus. These impulses result in the:

Correct Answer: C

Rationale: Nipple stimulation sends signals to the hypothalamus, triggering oxytocin release from the posterior pituitary for milk ejection via myoepithelial contraction. Prolactin, for milk synthesis, comes from the anterior pituitary, not posterior, and isn't 'lactogenic' specifically here. Prolactin-inhibiting factor (dopamine) suppresses prolactin, not aiding lactation. Oxytocin's ejection role distinguishes it, critical for nursing, unlike synthesis or inhibitory actions.

Correct Answer: B

Rationale: G proteins activate adenylyl cyclase in cAMP signaling, converting ATP to cAMP to amplify signals (e.g., epinephrine response). Blocking G protein prevents this activation, halting cAMP production. Hormone binding occurs upstream, excessive cAMP or phosphorylation would require activation. This inhibition distinguishes the direct effect, key to understanding second messenger disruptions in cellular signaling pathways.

Correct Answer: C

Rationale: Iodide enters thyroid follicle cells via active transport, using the sodium-iodide symporter (NIS), against its gradient, powered by sodium's electrochemical gradient. Simple diffusion lacks a carrier, facilitated diffusion doesn't use energy, and osmosis moves water. Active transport's energy dependence distinguishes it, essential for thyroid hormone synthesis, concentrating iodide for T3/T4 production.

Correct Answer: C

Rationale: Gonads (ovaries, testes) produce steroid hormones estrogens, progesterone, testosterone from cholesterol, acting intracellularly to regulate reproduction. Amine hormones (e.g., thyroid) derive from tyrosine, peptides (e.g., insulin) from amino acids, and catecholamines (e.g., epinephrine) from adrenal medulla. Steroid's lipid-based nature distinguishes gonadal output, critical for sexual development, contrasting with other chemical classes.

Correct Answer: A

Rationale: The anterior pituitary arises from oral ectoderm, specifically Rathke's pouch, during embryogenesis, forming hormone-secreting cells. Neural ectoderm forms the nervous system (including posterior pituitary), mesoderm muscles/bones, and endoderm digestive organs. Oral ectoderm origin distinguishes anterior pituitary development, key to its endocrine role, contrasting with neural or internal layer derivatives.