Chemical signaling that affects neighboring cells is called

Correct Answer: B

Rationale: Paracrine signaling involves chemicals, like prostaglandins, affecting nearby cells, as in inflammation. Autocrine signals target the secreting cell itself (e.g., cancer cells), endocrine signals travel via blood to distant targets, and 'neuron' isn't a signaling type neurons use neurotransmitters. Paracrine's local action distinguishes it, key for short-range cellular communication, contrasting with self-directed or systemic signaling in physiological responses.

Correct Answer: B

Rationale: Pinealocytes in the pineal gland secrete melatonin to regulate sleep-wake cycles, influenced by light. Melanocytes produce pigment, suprachiasmatic nucleus cells regulate circadian rhythms but don't secrete melatonin, and retinal cells detect light. Pinealocytes' secretory role distinguishes them, vital for circadian control, contrasting with pigment or regulatory cells.

Correct Answer: C

Rationale: Erythropoietin (EPO), from kidneys, stimulates red blood cell production, increasing oxygen-carrying capacity enhancing endurance. It doesn't affect calcium, growth hormone, or muscle mass directly (testosterone does). Oxygen boost distinguishes EPO's use, key to athletic performance, contrasting with skeletal or hormonal growth effects.

Correct Answer: C

Rationale: Gonads (ovaries, testes) produce steroid hormones testosterone, estrogen, progesterone from cholesterol, acting on nuclear receptors for sex traits and reproduction. Amine hormones (e.g., thyroxine) derive from tyrosine/tryptophan, from thyroid. Peptide hormones (e.g., insulin) are protein-based, from pancreas. Catecholamines (e.g., epinephrine) are adrenal medullary, not gonadal. Steroids' lipid-soluble, genomic action distinguishes them, critical for gonadal endocrine function, unlike amino-acid or peptide classes.

Correct Answer: C

Rationale: Melatonin, from the pineal gland, regulates sleep-wake cycles, peaking in darkness to induce sleep, reducing arousal and cortisol darkness triggers, light inhibits it. The false statement reverses this: light suppresses melatonin, resetting circadian rhythms, while darkness stimulates it. Heat loss and rhythm regulation are true effects; pineal production is accurate. This light-dark dynamic distinguishes melatonin's role, critical for circadian alignment, unlike inverted or correct functions.