A 40-year-old woman notes lethargy, weakness, and constipation for the past 6 months. On physical examination, she is afebrile and normotensive, and her heart rate is irregular. There is pain on palpation of the left third proximal finger. An ECG shows a prolonged QT (corrected) interval. Laboratory studies show glucose, 73 mg/dL; creatinine, 1.2 mg/dL; calcium, 11.6 mg/dL; phosphorus, 2.1 mg/dL; total protein, 7.1 g/dL; albumin, 5.3 g/dL; and alkaline phosphatase, 202 U/L. A radiograph of the left hand shows focal expansion by a cystic lesion of the third proximal phalanx. A technetium radionuclide scan shows a 1-cm area of increased uptake in the right lateral neck. A mutation in which of the following genes is most likely present in this woman?

Correct Answer: B

Rationale: A parathyroid neoplasm, most likely an adenoma, is causing hypercalcemia complicated by osteitis fibrosa cystica of her finger. Parathyroid hyperplasia involving all the glands is less likely. Parathyroid carcinomas are rare, thankfully, because they are aggressive, and serum calcium levels may be so high that cardiac arrhythmias occur. The MEN1 mutation is the second most common mutation in parathyroid tumors, after the inversion with overexpression of CCND1, the gene encoding cyclin D1. MEN1 is a tumor suppressor gene, the loss of which occurs not only in sporadic parathyroid tumors, but also in multiple endocrine neoplasia (MEN) type 1.

Correct Answer: D

Rationale: All statements are true: slow response, hormones travel via blood, nervous input modifies it, but it uses endocrine (not exocrine/apocrine) glands "still considered broadly correct per answer key.

Correct Answer: C

Rationale: AP triggers vesicle fusion, releasing ACh into cleft; then Na+ channels open, AChE acts later.

Correct Answer: D

Rationale: All occur: S1 marks AV closure, pressure rise, isovolumetric phase, QRS.

Correct Answer: D

Rationale: Capillaries reabsorb fluid via oncotic pressure at venous end.