STEP1 Exam dumps PDF | Exam-Dumps (Page: 21)

QUESTION: 101

During surgery to repair a strangulated inguinal hernia, it is discovered that the left testicular vein is thrombosed and must be repaired. The left testicular vein normally drains into which of the following?

inferior vena cava
left renal vein
right common iliac vein
right femoral vein
right renal vein

Answer(s): B

Explanation:

The left testicular vein drains into the left renal vein. The inferior vena cava (choice A) receives the right testicular vein. The equivalent relationship holds true in the female where the left ovarian vein drains into the left renal vein and the right ovarian vein into the inferior vena cava. The right common iliac vein (choice C), right femoral vein (choice D), and right renal vein (choice E) do not receive gonadal veins.

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QUESTION: 102

The sensory innervation of the posterior onethird of the tongue is performed by cranial nerve IX (glossopharyngeal). During development, this region of the tongue develops from which of the following pharyngeal arches?

first
fourth
second
sixth
third

Answer(s): E

Explanation:

The posterior one-third of the tongue is derived from the third pharyngeal arch and is thus innervated by cranial nerve IX (glossopharyngeal). The first pharyngeal arch (choice A) and second pharyngeal arch (choice C) give rise to the anterior two-thirds of the tongue. The mandibular division of cranial nerve V (trigeminal) provides general sensation to the anterior two-thirds of the tongue, and cranial nerve VII via the chorda tympani provides special sensation (taste). The fourth pharyngeal arch (choice B) gives rise to the epiglottis and, along with the sixth pharyngeal arch (choice D), to the laryngeal cartilages. The nerve to the fourth pharyngeal arch is cranial nerve X (vagus).

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QUESTION: 103

The sinoatrial (SA) node initiates the heartbeat by giving off an impulse about 80 times per minute. It is located at the junction of the superior vena cava and right atrium. In about 60% of the cases, the SA node derives its vascular supply from which of the following?

anterior interventricular artery
left circumflex artery
posterior interventricular artery
right coronary artery
right marginal branch

Answer(s): D

Explanation:

In 60% of patients, the right coronary artery supplies the SA node. In a third of the population, the SA node is supplied by the left coronary artery and in some patients it receives branches from both the right and the left. The anterior interventricular (choice A) and left circumflex (choice B) arteries are distal branches of the left coronary artery, too distant to supply the SA node. The right coronary artery normally gives out its SA nodal branch in its proximal portion and then distally gives rise to the right marginal (choice E) and posterior interventricular (choice C) arteries. These are also too distant to supply the SA node.

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QUESTION: 104

In elderly patients (over 60 years of age), fractures of the neck of the femur following a fall are common. Arterial branches supplying the femoral head and neck are vulnerable to injury during these fractures, and the resulting posttraumatic avascular necrosis affects the head of the femur. In the adult, the most important direct vascular source to the femoral head and neck is which of the following?

artery to the head of the femur
femoral artery
lateral circumflex femoral artery
medial circumflex femoral artery
superior gluteal artery

Answer(s): D

Explanation:

The medial circumflex femoral artery supplies the most important source of blood to the femoral head and neck. This artery anastomoses with the artery to the head of the femur (choice A), which arises from the obturator artery. However, if the medial circumflex femoral artery is injured, the blood flow in the small artery to the head of the femur may not be sufficient to prevent posttraumatic avascular necrosis of the femoral head. Normally, the medial and lateral circumflex femoral arteries arise from the deep artery of the thigh, but occasionally they arise from the femoral artery (choice B). However, the femoral artery is not a direct vascular source to the head of the femur. The lateral circumflex femoral artery (choice C) and superior gluteal artery (choice E) also supply the hip joint, but their contribution to the head and neck of the femur is less than that of the medial femoral circumflex artery.

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QUESTION: 105

A 38-year-old female patient suffers from pleurisy and requires pleural fluid sampling (thoracentesis). The attending physician asks you to perform the procedure at the midaxillary line on the right side. Which of the following would be the appropriate level to perform the procedure?

above the level of the 7th rib
at the level of the 10th rib
at the level of the 5th rib
below the level of the 10th rib
between the level of the 8th and 10th ribs

Answer(s): E

Explanation:

The needle for thoracentesis should be inserted in the intercostals spaces between the 8th and 10th ribs.
Remember that the parietal pleura extends approximately two ribs inferior to the lung: at the midaxillary line, the inferior surface at the lung is at the level of the 8th rib and the parietal pleura at the 10th rib. Above the level of the 7th (choice A) and 5th (choice C) ribs, the needle will injure the lung. At (choice B) or below the level of the 10th rib (choice D), it will injure the liver or other abdominal organs.

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USMLE STEP1 Exam (page: 21) USMLE Step1 Updated on: 16-Feb-2026

QUESTION: 101

Explanation:

QUESTION: 102

Explanation:

QUESTION: 103

Explanation:

QUESTION: 104

Explanation:

QUESTION: 105

Explanation:

USMLE STEP1 Exam (page: 21)
USMLE Step1
Updated on: 16-Feb-2026