The hormone that maintains pregnancy is secreted by the

Correct Answer: C

Rationale: Progesterone, vital for maintaining pregnancy, is primarily secreted by the placenta after early ovarian production. 'Placenta,' is correct, per physiology texts like Guyton, sustaining uterine growth and preventing contractions. 'Anterior pituitary,' secretes FSH and LH, not progesterone directly. 'Ovary,' produces it initially via the corpus luteum, but the placenta takes over. 'Posterior pituitary,' releases oxytocin, not progesterone. The placenta's role post-first trimester, maintaining pregnancy through progesterone, distinguishes C as the accurate answer.

Correct Answer: B

Rationale: The nephron is the kidney's structural and functional unit, filtering blood and forming urine. 'Nephron,' is correct, per physiology texts like Vander, encompassing glomerulus and tubules. 'Glomerulus,' is part of the nephron. 'Renal artery,' supplies blood. 'Bowman's capsule,' encases the glomerulus within the nephron. The nephron's comprehensive role in filtration, reabsorption, and excretion makes B the precise answer.

Correct Answer: D

Rationale: Accessory digestive organs aid digestion outside the alimentary canal. 'Kidney,' is correct as the exception, filtering blood, not digesting, per physiology (e.g., Guyton). 'Liver,' produces bile. 'Pancreas,' secretes enzymes. 'Gall bladder,' stores bile. Kidney's excretory role distinguishes D as the accurate answer.

Correct Answer: C

Rationale: The peripheral nervous system (PNS) includes nerves outside the CNS. 'Spinal cord,' is correct as the exception, part of the CNS, per anatomy (e.g., Tortora). 'Cranial nerves,' and 'Spinal nerves,' are PNS. 'Autonomic nervous system,' is PNS's involuntary arm. Spinal cord's CNS role makes C the accurate answer.

Correct Answer: B

Rationale: The diaphragm is the primary muscle dividing thoracic and abdominal cavities, aiding respiration. 'Diaphragm,' is correct, per anatomy (e.g., Moore). 'Intercostal,' assists breathing between ribs. 'Rectus abdominis,' is abdominal. 'Pectoralis major,' is chest. Diaphragm's septal role makes B the accurate answer.