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USMLE STEP1 Exam Questions
Step1 (Page 14 )

Updated On: 31-Mar-2026
Page 14 of 171
PDF with 845 Questions

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?

  1. bronchial artery
  2. inferior thyroid artery
  3. internal thoracic artery
  4. left inferior gastric artery
  5. left inferior phrenic artery

Answer(s): B

Explanation:

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.



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?

  1. ectoderm
  2. endoderm
  3. mesenchyme
  4. notochord
  5. sclerotome

Answer(s): C

Explanation:

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.



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

  1. esophageal glands
  2. intestinal glands (of Lieberkün)
  3. the parotid gland
  4. the sublingual gland
  5. the submandibular gland

Answer(s): C

Explanation:

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.



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?

  1. alpha cells
  2. beta cells
  3. centroacinar cells
  4. delta cells
  5. F cells

Answer(s): C

Explanation:

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.



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?

  1. anterior cruciate ligament
  2. fibula
  3. fibular (lateral) collateral ligament
  4. posterior cruciate ligament
  5. tibial (medial) collateral ligament

Answer(s): A

Explanation:

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.



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