usmle习题

1、A 54-year-old man complains to his physician that he is having progressive discomfort in his leg during movement of the foot. On physical examination, the physician noted a decreased pulse in the dorsalis pedis artery. Compression of a blood vessel in which of the following locations would most likely result in this decreased blood flow of the dorsalis pedis artery?
A、Anterior compartment of the leg
B、Deep to the gastrocnemius and soleus muscles
C、Lateral compartment of the leg
D、Neck of the fibula
E、Posterior to the medial malleolus
正确选项：A
Choice "A" is the best answer. The dorsalis pedis artery is the distal continuation of the anterior tibial artery. The anterior tibial artery courses in the anterior compartment of the leg, where it can be compressed during anterior compartment syndrome and result in decreased pulse of the dorsalis pedis artery. Choice "B" is not the best answer. The gastrocnemius and soleus muscles are found in the posterior compartment of the leg and are associated with the posterior tibial artery, which passes posterior to the medial malleolus and supplies blood to the sole of the foot. Choice "C" is not the best answer. The lateral compartment contains fibularis longus and brevis muscles that evert the foot. This compartment receives blood supply from a branch of the posterior tibial artery. Choice "D" is not the best answer. The common fibular nerves divides into the superficial and deep fibular nerves on the lateral side of the knee at the neck of the fibula. This is one of the most common locations of nerve damage in the lower limb. Choice "E" is not the best answer. The tibial nerve and the posterior tibial artery are posterior to the medial malleolus to enter the sole of the foot.
2、A 25-year-old male is in a nightclub when he becomes involved in a physical altercation with another patron. A fight breaks out involving many participants and someone pulls a knife and stabs the patient in the right lateral chest. Emergency medical services are called and the patient is taken to a nearby trauma center via ambulance. On the way, the paramedic notices the patient’s right shoulder blade is protruding from the back. Heavy bleeding can occur from which structure, which could also have been damaged by the stab wound?
A、Brachial artery
B、Lateral thoracic artery
C、Posterior humeral circumflex artery
D、Subclavian artery
E、Suprascapular artery
正确选项：B
Choice "B" is the best answer. Wounds to the lateral chest can put the long thoracic nerve at risk, which can lead to "winging" of the scapula due to loss of enervation to the serratus anterior muscle. The lateral thoracic artery runs close to the long thoracic nerve and thus is also a danger with any injury that damages this nerve. Choice "A" is not the best answer. The brachial artery is the continuation of the axillary artery and supplies the arm. It courses in the cubital fossa, among other regions. Choice "C" is not the best answer. The posterior humeral circumflex artery courses along with the axillary nerve around the surgical neck of the humerus. Choices "D" and "E" are not the best answers. The suprascapular artery is a branch of the subclavian artery. Despite their proximity to the scapula,
3、A 27-year-old woman is pregnant at a gestational age of 31 weeks. She presents to the emergency department for pain in her right upper quadrant. Her blood pressure is 170/100 mmHg, she has headaches, 2+ bilateral pitting edema, and 3+ protein in her urine. Her white blood cell (WBC) count is 3000 mcl, red blood cells (RBC) count is 2.8 mcL, hemoglobin (Hgb) is 10.8 gm/dL, and platelets are also found to be 100,000 mcL. Her aspartate aminotransferase (AST) is 55 IU/L, gamma-glutamyl transferase (GGT) is 22 IU/L, alkaline phosphatase (ALP) is 45 IU/L, and total bilirubin is 1.0 mg/dL. Which of the following organs is the most likely cause of this patient's pain?
A、Appendix
B、Diaphragm
C、Gallbladder
D、Liver
E、Pancreas
正确选项：D
Choice "D" is the best answer. This patient presents with pre-eclampsia and HELLP syndrome (hemolysis, elevated liver enzymes, and low platelet count). Irritation of the Glisson capsule surrounding the liver causes right upper quadrant pain in these patients. Choice "A" is not the best answer. Appendicitis usually presents in the right lower quadrant, and her WBC count is not elevated. Her lab values are more consistent with pre-eclampsia and HELLP syndrome. Choice "B" is not the best answer. Irritation of the diaphragm localizes the pain to the chest, shoulders, or abdomen. Breathing would also be difficult or painful. The patient is not demonstrating these findings, so the diaphragm is likely not involved. Choice "C" is not the best answer. This patient's GGT, ALP, and bilirubin are not elevated, which makes problems with the gallbladder, such as cholestasis, less likely. Choice "E" is not the best answer. Pancreatitis usually presents in the upper half of the abdomen, and can also radiate to the back. However, her WBC count and ALP are normal, so these findings are more consistent with pre-eclampsia and HELLP syndrome.
4、A 50-year-old female comes to her doctor complaining of frequent hand numbness and tingling as well having repeated instances of "losing my grip on things." She also is struggling with an aching pain over the ventral part of her wrist. Her symptoms are worse sometimes when she drives and she occasionally wakes up from sleeping with the tingling sensation and pain in both wrists. Electrophysiologic studies confirm her doctor’s suspicion of carpal tunnel syndrome. Which of the following would be expected on physical exam?
A、Atrophy of hypothenar muscles
B、Loss of sensation on lateral palm
C、Strongly abducted thumb
D、Weakness in extending fourth and fifth digits at DIP and PIP joints
E、Weakness with thumb opposition
正确选项：E
Choice "E" is the best answer. Carpal tunnel syndrome arises when the space in the carpal tunnel is reduced, which can be caused by inflammation of the flexor retinaculum, inflammation of the tendon sheaths, or arthritis. Reduction causes compression of the median nerve. Signs of carpal tunnel syndrome include hand numbness and tingling of the fingers as well as pain over the ventral part of the wrist. Symptoms can be exacerbated by certain
activities or can manifest while sleeping. Compression of the median nerve leads to atrophy/flattening of the thenar muscles, sensory loss in the lateral three digits, and weakness of thumb. Choices "A," "C," and "D" are not the best answers. These findings would all be characteristic of injury to the ulnar nerve, which can occur as a result of damage to the medial side of the elbow, wrist trauma or a fracture of the hook of the hamate. Choice "B" is not the best answer. Although sensation to the lateral palm is supplied by the median nerve, the cutaneous branch of the median nerve that provides this sensation does not course through the carpal tunnel and thus would not be affected by carpal tunnel syndrome.
5、A 6-month old infant with a history of Tetralogy of Fallot and cleft palate is brought to the pediatric ER because he keeps having uncontrollable muscle spasms and "strange spots" are appearing on his skin.
A blood test reveals hypocalcemia. In addition to the patient’s above problems, the attending physician decides to do a blood culture because the patient is at risk for infection due to immunodeficiency. This patien t’s condition is the result of failure of differentiation of which embryological parts?
A、1st pharyngeal arch
B、1st and 2nd pharyngeal pouches
C、2nd and 3rd pharyngeal arches
D、3rd and 4th pharyngeal pouches
E、5th pharyngeal arch
正确选项：D
Choice "D" is the best answer. The patient has DiGeorge syndrome, which is marked by the lack of differentiation of the third and fourth pharyngeal pouches. DiGeorge syndrome often is first suspected in patients with congenital cardiac defects (such as Tetralogy of Fallot, truncus arteriosus, and an interrupted aortic arch) and hypocalcemia. These patients also commonly have a cleft palate. Other manifestations such as distinct craniofacial abnormalities and defective T-cell-based immunity can become apparent later in life. The hypocalcemia in these patients is due to failure of the inferior and superior parathyroids to develop. Choice "A" is not the best answer. Failure of the first pharyngeal arch to develop causes different forms of first arch syndrome, such as Treacher Collins syndrome and Pierre Robin syndrome. First arch syndrome results in abnormal development of many different facial structures, such as the
eyes, mandible, ears, and palate. Choice "B" is not the best answer. The first and second pharyngeal pouches give rise to the epithelial linings of the auditory tube, middle chamber of the ear, and palatine tonsils. Choice "C" is not the best answer. The second pharyngeal arch gives rise to muscles of facial expression and the stapes and styloid process, as well as the lesser horn and upper body of the hyoid. The third pharyngeal arch gives rise to the stylopharyngeus muscle, parts of the hyoid bone, and the common and internal carotid arteries. Choice "E" is not the best answer. The fifth pharyngeal arch regresses during development and does not form any structures.
6、A newborn baby is identified as having a heart defect. Clinical evaluation indicates that the right heart is enlarged due to shunting of blood from the left to the right atrium. A large, high atrial septal defect is identified superior to the limbus. Which of the following is characteristic of this newborn’s defect?
A、Cyanotic defect
B、Interventricular septal defect
C、Neural crest migration defect
D、Patent first foramen (primum)
E、Patent foramen ovale
正确选项：E
Choice "E" is the best answer. The atrial septal defect (ASD) described in this newborn is a high defect located superior to the limbus and fossa ovalis of the interatrial wall, indicating that it is a secundum-type atrial septal defect. This defect results from a failure of the septum primum and secundum to overlap during development, resulting in a patent foramen ovale. This defect is noncyanotic at birth. Choice "A" is not the best answer. Atrial septal defects at birth shunt blood left to right and are not cyanotic. Choice "B" is not the best answer. The most common of newborn heart defects is an interventricular septal defect (VSD), which most often involves the membranous part of the interventricular septum. Choice "C" is not the best answer. This type of ASD does not result from the failure of neural crest migration. Choice "D" is not the best answer.
A primum defect occurs in the lower part of the interatrial septum and often involves neural crest migration into the endocardial cushion.
7、The ductus arteriosus is one of several vascular shunts that develops during fetal circulation. The function of the ductus arteriosus in the fetus is correctly described by which of the following statements?
A、Bypasses the lungs with oxygenated blood
B、Shunts deoxygenated blood from the pulmonary artery to the aorta
C、Shunts deoxygenated blood from the pulmonary veins to the left atrium
D、Shunts oxygenated blood from the aorta to the pulmonary artery
E、Shunts oxygenated blood from the pulmonary artery to the aorta
正确选项：B
Choice "B" is the best answer. The ductus arteriosus arises distal to the origin of the subclavian artery and shunts blood during fetal life from the pulmonary trunk to the aorta. Most of the blood passing through the ductus is systemic, deoxygenated blood that has returned to the heart through the superior vena cava and passed through the right ventricle into the pulmonary artery. Choice "A" is not the best answer. The ductus arteriosus does bypass the lungs, but with deoxygenated blood. Choice "C" is not the best answer. The ductus does not shunt blood from the pulmonary veins to the left atrium. Choice "D" is not the best answer. The shunting of oxygenated blood from the aorta to the pulmonary artery occurs with a patent ductus arteriosus. Choice "E" is not the best answer. During fetal life, the ductus shunts deoxygenated blood from the pulmonary artery to the aorta.
8、A 45-year-old man comes to the emergency department with crushing chest pain. His lab studies reveal elevated cardiac enzymes, suggesting a myocardial infarction. His ECG confirms akinetic segments in an area of the interventricular septum that contains the bundle of His. Which coronary vessel is most likely obstructed?
A、Anterior interventricular coronary artery
B、AV nodal artery
C、Circumflex coronary artery
D、Posterior interventricular coronary artery
E、Right coronary artery
正确选项：A
Choice "A" is the best answer. The interventricular septum has two blood supplies. The anterior aspect of the interventricular septum, which contains the bundle of His, is supplied by the anterior interventricular
artery (left anterior descending), which is the area indicated by the myocardial infarction in this question. The posterior part of the septum is supplied by the posterior interventricular artery. Choice "B" is not the best answer. The AV nodal artery is one of the first branches of the right coronary artery and supplies the AV node, which is not in the area supplied by the anterior interventricular artery. Choice "C" is not the best answer. The circumflex artery is one of the two branches of the left coronary artery, which supplies the posterior ventricular wall and the left border of the heart. Choice "D" is not the best answer. The posterior interventricular artery is the distal termination of the right coronary artery and supplies the posterior part of the interventricular septum. Choice “E” is not the best answer. The right coronary artery is one of the two major coronary arteries that supplies most of the right side of the heart and does not supply the anterior part of the interventricular septum.
9、A 25-year-old soldier is serving in a combat zone when an explosive goes off nearby, sending shrapnel into his shoulder and neck. The resulting damage and swelling affects all three of his brachial plexus trunks, but leaves the roots intact. Despite his widespread injuries, which of the following muscles would still retain innervation?
A、Biceps brachii
B、Deltoid
C、Latissimus dorsi
D、Pectoralis major
E、Serratus anterior
正确选项：E
Choice "E" is the best answer. The serratus anterior muscle is innervated by the long thoracic nerve, which is formed from roots C5 and C6 and is formed before the nerve roots combine into trunks. Thus, it could surviv e damage to all three nerve trunks. Choice “A” is not the best answer. The biceps brachii muscle is innervated by the musculocutaneous nerve which branches from the lateral cord. Choice "B" is not the best answer. The deltoid is innervated by the axillary nerve, which comes off of the posterior cord. An injury to the trunks (that give rise to the cords) would affect the function of the deltoid. Choice "C" is not the best answer. The latissimus dorsi is innervated by the thoracodorsal (middle subscapular) nerve, which comes off the posterior cord. Choice
“D” is not the best answer. The pectoralis major muscle is innervated by the lateral pectoral nerve (which comes from the lateral cord) and the medial pectoral nerve (which arises from the medial cord).
10、A 25-year-old man complains to his physician that he has lost sensation in his right hand. The physical exam shows that there is loss of two-point discrimination and vibration in his hand. Which of the following is part of the neural pathway for these functions?
A、Left fasciculus cuneatus
B、Left spinothalamic tract
C、Right cuneate nucleus
D、Right lateral funiculus
E、Ventral white commissure
正确选项：C
Choice "C" is the best answer. The sensory loss of touch and vibration on the right hand indicates a lesion of the dorsal column-medial lemniscus pathway. The only possible site for the lesion listed in this question would be the right cuneate nucleus, which is before the decussation of the pathway in the lower medulla. Choice "A" is not the best answer. The loss of sensation is on the right hand and the nucleus lesion would have to be on the ipsilateral side. Choice "B" is not the best answer. The spinothalamic tract is responsible for conduction pain and temperature sensations. Choice "D" is not the best answer. The lateral funiculus is the lateral aspect of the white matter of the spinal cord does not contain the tracts that carry touch and two-point discrimination. Choice "E" is not the best answer. The ventral white commissure is the decussation site at the central area of the spinal cord for the spinothalamic tract.。