USMLE

Which of the following is the primary opsonin in the complement system?

A 37-year-old female presents to the emergency room with a fever. Chest x-ray shows multiple patchy infiltrates in both lungs. Echocardiography and blood cultures suggest a diagnosis of acute bacterial endocarditis limited to the tricuspid valve. Which of the following is the most probable etiology?

A baby who was apparently normal at birth, develops persistent regurgitation and vomiting in the second and third weeks of life. No fever is present and hematologic studies and blood chemistries are normal. Which of the following therapies is most likely to be effective in this case?

A 24-year-old woman in her third trimester of pregnancy presents with urinary frequency and burning for the past few days. She denies fever, nausea, vomiting, or chills. She takes no medications besides prenatal vitamins and is generally in good health. Physical examination is remarkable for mild suprapubic tenderness, and a urine dipstick is positive for white blood cells, protein, and a small amount of blood. Culture produces greater than 100,000 colonies of gram-negative bacilli. which of the following attributes of this uropathogenic organism is most strongly associated with its virulence?

A 20-year-old develops weakness accompanied by difficulty in relaxation that is most pronounced in the hands and feet. Muscle biopsy demonstrates prominent ring fibers, centrally located nuclei, chains of nuclei, and disorganized sarcoplasmic masses. This condition been associated with a mutation on which of the following chromosomes?

Which of the following hormones is secreted by anterior pituitary cells that stain with acidic dyes?

A 36-year-old Asian male complains of difficulty swallowing. Esophagoscopy reveals a polypoid mass that is subsequently biopsied.  In addition to tumor cells, the esophageal biopsy show normal smooth  muscle and striated muscle in the same section. Which portion of the  esophagus was the source of this biopsy?

Which of the following respiratory system components is derived

The heart of an embryo first begins beating at which of the following ages?

A neuroscientist is investigating the development of the nervous system. In his experiments, he microinjects a dye into the embryo of  an animal subject in vivo. After birth, he performs histological  studies to determine the destination of the dye. In one animal subject,  he locates the dye in the dorsal horn of the spinal cord. Which of the  following locations in the embryo was the most likely site of the injection?