Secretion of oxytocin is increased by

Correct Answer: B

Rationale: Certainly! The secretion of oxytocin is increased by the dilation of the cervix. When the cervix dilates during childbirth, it triggers the release of oxytocin from the posterior pituitary gland. This hormone plays a crucial role in stimulating uterine contractions during labor and delivery. Milk ejection (choice A) is primarily regulated by oxytocin but does not directly increase its secretion. Increased prolactin levels (choice C) stimulate milk production, not oxytocin secretion. Increased extracellular fluid (ECF) volume (choice D) is not directly related to oxytocin secretion.

Correct Answer: A

Rationale: The correct answer is A: the heart. Atrial Natriuretic Peptide (ANP) is synthesized and released by the atrial cells of the heart in response to stretching of the atrial wall due to increased blood volume or pressure. ANP functions to regulate blood pressure and fluid balance by promoting natriuresis and vasodilation. The kidney (choice B) is responsible for filtering blood and regulating electrolyte balance, but it does not synthesize ANP. The skin (choice C) is involved in thermoregulation and vitamin D synthesis, not ANP production. The spleen (choice D) plays a role in immune function and blood storage, but it does not synthesize ANP.

Correct Answer: C

Rationale: The correct answer is C: liver. The liver does not produce hormones. Hormones are primarily produced by endocrine glands such as the pituitary, thyroid, adrenal glands, etc. The liver's main functions are related to metabolism, detoxification, and storage, rather than hormone production. The heart (choice A) produces hormones like atrial natriuretic peptide. The kidney (choice B) produces hormones like erythropoietin and renin. The skin (choice D) produces hormones like vitamin D when exposed to sunlight. Therefore, the liver is the only organ in the list that does not have hormone production.

Correct Answer: C

Rationale: The correct answer is C: cAMP and calcium. Peptide hormones bind to their receptors on the cell surface, activating G-proteins which then trigger the production of cAMP as a second messenger. cAMP then further activates protein kinases to initiate various cellular responses. Calcium is also a common second messenger in peptide hormone signaling pathways, regulating processes like muscle contraction and gene expression. Choice A is incorrect because peptide hormones themselves are not second messengers. Choice B is incorrect as glucose is not a common second messenger for peptide hormones. Choice D is incorrect as sodium is not typically involved in peptide hormone signaling pathways.

Correct Answer: B

Rationale: Step 1: The hormones produced by the hypothalamus and secreted by the posterior pituitary are ADH (vasopressin) and oxytocin. Step 2: ADH regulates water balance by increasing water reabsorption in the kidneys. Step 3: Oxytocin is involved in uterine contractions during childbirth and milk ejection during breastfeeding. Step 4: Therefore, choice B (ADH and oxytocin) is correct. Summary: - Choice A (ADH and aldosterone) is incorrect because aldosterone is produced by the adrenal glands, not the posterior pituitary. - Choice C (oxytocin and prolactin) is incorrect because prolactin is produced by the anterior pituitary. - Choice D (cortisol and aldosterone) is incorrect because cortisol is produced by the adrenal glands, not the posterior pituitary.