USMLE USMLE Certifications USMLE-STEP-1 Questions & Answers

• Question 781:

  A 35-year-old male patient suffering from pulmonary hypertension has been diagnosed with ostium secundum atrial septal defect. Abnormal development of which of the following structures is responsible for this developmental defect?

  A. aorticopulmonary septum

  B. endocardial cushion

  C. interventricular septum

  D. septum primum

  E. sinus venosus

  Correct Answer: D

  Section: Anatomy Abnormal development of either the septum primum or septum secundum results in ostium secundum atrial septal defects in the area of the fossa ovalis. This common type of congenital heart defect is manifested by a patent foramen ovale between right and left atria. This is well-tolerated during childhood, but symptoms usually appear after 30 years of age. The aorticopulmonary septum (choice A) divides the truncus arteriosus of the developing heart and gives rise to the ascending aorta and pulmonary trunk. The endocardial cushions (choice B) give rise to the right and left atrioventricular canals. The interventricular septum (choice C) forms between the right and left ventricles. The sinus venosus (choice E) becomes incorporated into the atria, as well as giving rise to the openings of the pulmonary veins and the venae cavae.

• Question 782:

  In this same patient, the pectineus muscle is also badly bruised. This muscle is innervated by which of the following?

  A. genitofemoral nerve

  B. obturator nerve

  C. peroneal division of the sciatic nerve

  D. saphenous nerve

  E. tibial division of the sciatic nerve

  Correct Answer: B

  Section: Anatomy The pectineus muscle is part of the adductor muscles of the thigh, which are innervated as a group by the obturator nerve. The genitofemoral nerve (choice A) provides sensory innervation for a small area of the skin in the medial superior aspect of the thigh, and motor innervation to the cremaster muscle. The peroneal division of the sciatic nerve (choice C) innervates the skin and muscles in the peroneal and anterior comparments of the leg. The saphenous nerve (choice D) is purely a sensory nerve for the medial aspect of the leg and the foot. The tibial division of the sciatic nerve (choice E) provides sensory and motor innervations to the posterior compartment of the leg and the plantar foot.

• Question 783:

  Serous cells are glandular acinar cells that produce a watery, proteinaceous fluid. This cell type is most predominant in which of the following glands?

  A. esophageal glands

  B. intestinal glands (of Lieberkün)

  C. the parotid gland

  D. the sublingual gland

  E. the submandibular gland

  Correct Answer: C

  Section: Anatomy The parotid gland is the only major salivary gland containing almost exclusively serous secretory cells. Esophageal (choice A) and intestinal glands (choice B) are small mucus-secreting glands. The sublingual (choice D) and submandibular glands (choice E) are mixed glands with differing proportions of serous and mucous cells.

• Question 784:

  Amember of a college fraternity, who had consumed a large amount of alcohol on a dare, is brought to the emergency room with vomiting and severe abdominal pain. Blood tests reveal that he has elevated serum levels of amylase and lipase. Atentative diagnosis of acute hemorrhagic pancreatitis is formulated. Which cells of the pancreas are directly involved in this condition?

  A. alpha cells

  B. beta cells

  C. centroacinar cells

  D. delta cells

  E. F cells

  Correct Answer: C

  Section: Anatomy Centroacinar cells are components of the exocrine pancreas and they contain zymogen granules, which are released under the action of cholecystokinin from the duodenum. The zymogen granules contain inactive proenzymes that normally become activated within the duodenum. Premature activation of the pancreatic enzymes, such as trypsin, leads to autodigestion of the centroacinar cells of the pancreatic acini, which secrete these enzymes. This results in acute hemorrhagic pancreatitis which can be caused by excessive alcohol ingestion. All the other choices are cells of the endocrine pancreas, which secrete hormones. Alpha cells (choice A) secrete glucagon whereas beta cells (choice B) produce insulin. Delta cells (choice C) synthesize gastrin and somatostatin. F cells produce pancreatic polypeptide.

• Question 785:

  A football player was simultaneously tackled from the front above the knee and from the back below the knee. In the emergency room, he displays a positive anterior drawer test which becomes negative if the knee is internally or externally rotated. Which of the following has ruptured?

  A. anterior cruciate ligament

  B. fibula

  C. fibular (lateral) collateral ligament

  D. posterior cruciate ligament

  E. tibial (medial) collateral ligament

  Correct Answer: A

  Section: Anatomy In the anterior drawer test, the patient's tibia is pulled forward and anterior tibial displacement reveals rupture of the anterior cruciate ligament. The drawer test becomes negative when the knee is internally rotated because of the tightening of the posterior cruciate ligament (choice D); in this case, the result reveals that the posterior cruciate ligament is not affected. External rotation is limited by the tibial (medial) collateral ligament (choice E) and since the drawer sign is negative with the knee in this position, this ligament is also intact. The fibula (choice B) and fibular colateral ligament (choice C) do not participate in the knee joint and have no effect on the drawer test.

• Question 786:

  A newborn female infant cannot swallow, exhibits persistent drooling, and aspiration or regurgitation of food after attempted feedings. When the infant strains, coughs, or cries, the stomach inflates, elevating the diaphragm and making respiration more difficult. The patient is diagnosed with congenital esophageal atresia at the cervical levels, necessitating surgical repair. During the surgery, the blood supply of the esophagus must be carefully isolated to protect from injury. Which of the following arteries supplies the esophagus at cervical levels?

  A. bronchial artery

  B. inferior thyroid artery

  C. internal thoracic artery

  D. left inferior gastric artery

  E. left inferior phrenic artery

  Correct Answer: B

  Section: Anatomy The inferior thyroid artery provides for the majority of the blood supply of the esophagus at cervical levels. It can be assisted by branches from the common carotid, subclavian, vertebral, ascending pharyngeal, superficial cervical, and costocervical arteries. The bronchial arteries (choice A) supply the thoracic portion of the esophagus and maybe assisted in the lower part by branches of the internal thoracic artery (choice C). The abdominal portion of the esophagus is vascularized by branches from the left inferior gastric artery and left inferior phrenic artery.

• Question 787:

  During development, the upper limb buds appear by day 27 and the lower limb buds by day 29. An apical ectodermal ridge at the tip of each limb bud promotes growth. This multilayered epithelial structure interacts with which of the following to direct the growth of the limb?

  A. ectoderm

  B. endoderm

  C. mesenchyme

  D. notochord

  E. sclerotome

  Correct Answer: C

  Section: Anatomy The apical ectodermal ridge secretes fibroblast growth factors, which act on mesenchymal cells in the zone of polarizing activity at the posterior margin of the limb bud. Activation of the zone of polarizing activity causes expression of the sonic hedgehog gene. Proteins expressed by the sonic hedgehog gene control the anteroposterior developmental pattern of the limb. The apical ectodermal ridge is contained within the ectoderm (choice A) and has no interaction with the endoderm (choice B). The notochord (choice D) and sclerotome (choice E) are structures involved in the development of the axial skeleton and not the limbs.

• Question 788:

  A 1-year-old infant presents with cardiomegaly and congestive heart failure. She has increased intracranial pressure with hydrocephaly and cranial bruit. A vein of Galen aneurysm, revealed by MRI, is shown to compress the aqueduct of Sylvius, the posterior part of the third ventricle, and the splenium of the corpus callosum. Normally, the cerebral vein of Galen joins with which dural venous sinus?

  A. inferior sagittal sinus

  B. sigmoid sinus

  C. superior petrosal sinus

  D. superior sagittal sinus

  E. transverse sinus

  Correct Answer: A

  Section: Anatomy The great cerebral vein of Galen joins with the inferior sagittal sinus to form the straight sinus. The latter drains into the transverse sinus (choice E). The superior sagittal sinus (choice D) drains posteriorly into the transverse sinus. The transverse sinus which runs bilaterally on the posterior wall of the posterior cranial fossa becomes the sigmoid sinus (choice B) which flows into the internal jugular vein. The superior petrosal sinus (choice C) extends from the cavernous sinus to the beginning of the sigmoid sinus.

• Question 789:

  Hormone-secreting chromophils in the pars distalis of the adenohypophysis are classified into acidophils and basophils. Which of the following hormones is secreted by the acidophils?

  A. adrenocorticotropin

  B. follicle-stimulating hormone

  C. luteinizing hormone

  D. prolactin

  E. thryrotropin (thyroid-stimulating hormone)

  Correct Answer: D

  Section: Anatomy Prolactin is secreted by one of the two types of hormone-secreting acidophils, the mammotrophs. The other types of acidophils are the somatotrophs, which secrete growth hormone (somatotropin). The hormones listed in all the other choices are secreted by the basophils. Adrenocorticotropin (choice A) is secreted by the corticotrophs. The gonadotrophs secrete either follicle-stimulating hormone (choice B) or luteinizing hormone (choice C). Thyrotropin (choice E) is secreted by thyrotrophs.

• Question 790:

  Production of specific granules occurs mainly during which stage of granulocyte development?

  A. granulocyte colony-forming unit

  B. metamyelocyte

  C. myeloblast

  D. myelocyte

  E. promyelocyte

  Correct Answer: D

  Section: Anatomy Generation of specific granules occurs during the myelocyte stage. Development of all three types of granulocytes follows a similar sequence of stages. The granulocyte colonyforming unit (choice A) is an undifferentiated progenitor cell of the granulocyte line. Buildup of the protein synthesis machinery occurs during the myeloblast (choice C) and promyelocyte (choice E) stages. The promyelocyte stage is also characterized by production of primary (nonspecific) granules. After the myelocyte stage, further condensation and reshaping of the nucleus occurs during the metamyelocyte stage (choice B).