Answers and Explanations

1. Answer: E. The spleen is a hemopoietic and lymph organ derived from mesoderm.

2. Answer: E. An omphalocele is caused by a failure of the midgut to return to the abdominal cavity after herniation into the umbilical stalk. Choices A and D may be seen in infants with Down syndrome; choice D is the specific cause of duodenal atresia. Choice C is the cause of gastroschisis, and Choice B results in a Meckel diverticulum.

3. Answer: A- Club foot, facial anomalies, and pulmonary hypoplasia are three features seen in bilateral renal agenesis (Potter sequence). Urachal cyst may be seen if the allantois fails to completely degenerate. Berry aneurysms are seen in patients with adult polycystic kidney disease. Situs inversus is seen when the midgut fails to rotate properly. Gastroschisis is a ventral body wall defect in which there is a herniation of the midgut at a weak point where the right umbilical vein regressed.

4. Answer: B. The fundus of the stomach is supplied by short gastric branches of the splenic artery. The splenic artery supplies the body and tail of the pancreas, part of the greater curvature of the stomach, and the spleen. The jejunum, part of the head of the pancreas, and the duodenum distal to the entrance of the common bile duct are supplied by the superior mesenteric artery, and the lesser curvature and the pyloric antrum are supplied by the right and left gastric arteries.

5. Answer: C. The omental bursa, or lesser peritoneal sac, lies directly posterior to the proximal part of the duodenum and the stomach and would be the first site where stomach contents would be found

6. Answer: C. A defect in a pleuroperitoneal membrane (usually the left) is the typical site of a congenital diaphragmatic hernia where the membrane fails to close one of the pericardioperitoneal canals.

7. Answer: E. Duodenal atresia and aganglionic megacolon are congenital defects seen in patients with Down syndrome.

8. Answer: D. Enlargement of and retrograde flow in gastric veins, in particular the left gastric veins, dilates the capillary bed in the wall of the esophagus in cases of portal hypertension. Blood flow would increase in and dilate tributaries of the azygous vein on the other side of the capillary bed, but flow in this vein is in the typical direction toward the superior vena cava. Paraumbilical vein engorgement contributes to a caput medusa. Splenic enlargement might present with splenomegaly, and backflow in to the superior mesenteric vein occurs but is asymptomatic.

9. Answer: D. Both of the ejaculatory ducts empty sperm from the epididymis by way of the ductus deferens and seminal fluid from the seminal vesicle into the prostatic urethra. Seminal fluid then traverses the membranous urethra in the urogenital diaphragm and penile urethra during ejaculation.

10. Answer: D. The patient has an indirect inguinal hernia, which emerges from the anterior abdominal wall through the deep inguinal ring. The deep ring is a fault in the transversal) s fascia; this layer will be penetrated first by the hernia.

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Answer: C. The ilioinguinal nerve, which provides sensation to the medial thigh and anterior scrotum, passes through the superficial inguinal ring and is subject to injury because it is in the operation field of the herniorrhaphy.

Answer: B. The lesser splanchnic nerves are sympathetic nerves that carry visceral sensations from inflamed or stretched gastrointestinal structures (in this case the appendix) into the CNS. Lesser splanchnic nerves arise from the T9-T12 spinal cord segments and provide sympathetic innervation to midgut structures, which include the appendix. Visceral pain arising from affected midgut structures is referred over the same dermatomes of spinal segments, which provide the sympathetic innervation. In this case of appendicitis, the involvement of the area of the umbilicus includes the T10 dermatome.

Answer: B. These folds must fuse to form the ventral aspect of the penis and scrotum. Here, the penile urethra opens onto the ventral aspect of the penis. Degeneration of the ureteric bud is a cause of oligohydramnios. Absence of androgen receptors in the external genitalia and 5 alpha-reductase 2 deficiency are causes of testicular feminization syndrome and stunted growth of male external genitalia, respectively Inadequate production of mullerian inhibitory substance is also caused by a 5 alpha-reductase 2 deficiency.

Answer: E. Compression of the prostatic urethra may also compress the ejaculatory duct and limit flow of seminal fluid from the ampulla of the ductus deferens and seminal vesicle through the ejaculatory duct and into the prostatic urethra. A hydrocele is caused by a small fluid accumulation in a patent remnant of the processus vaginalis. Urine leaking from the umbilicus might occur only if a patent urachus is present. In older men, compression of the prostatic urethra results in an increase in urinary pressure and filling of a patent urachus. Retrograde flow of the urine through the patent urachus may result in leaking of urine from the umbilicus. Urinary incontinence due to weakness of the sphincter urethrae muscle may be caused by a lesion of the pudendal nerve. A varicocele is an accumulation of venous blood in the pampiniform plexus of the testicular vein, which may be caused by compression of the left renal vein.

Answer: A. Prostate surgery may affect the branches of pelvic splanchnic nerves, which innervate the prostate and then course to the erectile tissues of the penis. The levator ani is innervated by skeletal motor branches from S2-S4. The pudendal nerve carries general sensation from the perineum and innervates external anal and urethral sphincters. Sympathetic nerves prevent retrograde ejaculation.

Answer: C. The testis is supplied by a direct branch of the abdominal aorta. All other choices are supplied by branches of the internal iliac artery.

Answer: B. The ischial spine is palpated through the lateral wall of the vagina to guide the needle to the pudendal nerve at the point where it crosses the spine.

Answer: A. The skeletal sphincter urethrae or external urethral sphincter muscle is the bladder sphincter muscle under voluntary control and is innervated by the pudendal nerve. This muscle is located in the urogenital diaphragm.

Answer: C. Muscles in the pelvic diaphragm (levator ani) contract to increase intraabdominal pressure during the Valsalva maneuver.

Answer: B. Of the five choices, only the descending colon is retroperitoneal and would be a likely choice to be seen immediately adjacent to the posterior abdominal wall.

21. Answer: D. Herniation of abdominal structures into the fetal thorax may impede lung development.

22. Answer: D. The splenic vein courses posterior to the body of the pancreas on its way to drain into the superior mesenteric vein.

23. Answer: C. This is a case of complete androgen insensitivity syndrome (CA1S) in which a mutation in the androgen receptor gene renders the androgen receptors inactive. Thus, despite a male karyotype, the external genitalia are female, but testes develop and attempt to descend through the inguinal canals.

24. Answer: D. The seminal vesicles lie on the posterior wall of the bladder and can be evaluated in a digital rectal exam.

25. Answer: B. The urogenital ridge and the paramesonephric duct are both derived from mesoderm, and primordial gametes are the only significant cell type derived from the wall of the yolk sac.

26. Answer: C. The ampulla of the uterine tube is the most common site of both fertilization and ectopic implantation.

27. Answer: D. Blood and fluid from a burst tubal pregnancy will accumulate in the pouch of Douglas.

28. Answer: C. The transverse cervical or cardinal ligaments are condensations of fascia in the base of the broad ligaments, which help prevent prolapse.

29. Answer: B. The gastroduodenal artery, a direct branch of the common hepatic artery, courses immediately posterior to the duodenum and is subject to erosion.

30. Answer: B. Carcinoma of the pancreas in the head may compress the portal vein at its origin. The portal vein is formed when the splenic vein joins with the superior mesenteric vein. The inferior mesenteric vein joins the splenic vein just prior to the point at which the splenic joins the superior mesenteric vein. Increased venous pressure in the inferior mesenteric vein is a cause of hemorrhoids.

31. Answer: E. The trigone of the bladder is directly anterior to the uterine cervix.

32. Answer: C. The fascia covering the penile urethra covers the superficial perineal pouch and is continuous with the deep fascia lining the anterior abdominal wall.

33. Answer: D. Gonadal carcinomas metastasize initially to para-aortic nodes.

34. Answer: C. The hepatic diverticulum, including the biliary apparatus, develops in the ventral mesentery of the foregut. The ventral pancreas, which forms most of the head of the pancreas, develops in the ventral mesentery as an outgrowth of the hepatic diverticulum.

35. Answer: C. The femoral vein lies immediately lateral to the femoral canal, the site of protrusion of a femoral hernia.

36. Answer: C. The upper part of the vagina is formed by a fusion of the paramesonephric ducts.

37. Answer: B. Berry aneurysms and mitrai valve prolapse are extrarenal manifestations of APKD.

38. Answer: A. The superior mesenteric vein joins with the splenic vein to form the hepatic portal vein.

39. Answer: C. The structure that contains contrast material is the ureter, which courses infe-riorly on the anterior surface of the psoas major muscle. It is derived from the ureteric bud, which is an outgrowth of the mesonephric duct.

40. Answer: D. The structure at "A" is the proper hepatic artery, which supplies oxygenated blood to the liver.

Ejaculatory Ducts Arise

Figure lll-4-1.The Brachial Plexus

MUSCLE INNERVATION

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