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A 71-year-old man has been in excellent health, and practicing competently as an attorney. He is brought to the emergency room following a motor vehicle accident. A workup, including imaging of the spine, thorax, and head, is negative, but the patient is admitted for overnight observation. His injuries include several lacerations to the face and extremities as well as several contusions to the thorax. Three weeks later, he is admitted to the hospital for confusion. A neurologic exam is normal except that he is not oriented to time or place, and can recall only 1 out of 6 objects after 3 minutes. Which of the following is the most likely diagnosis?

An 80-year-old woman dies after a long history of progressive memory loss, apraxia, and recurrent episodes of confusion. In the last months of life she was bedridden and unable to recognize familiar faces and objects. The pathologist identifies numerous flame-shaped intracytoplasmic inclusions in neurons of the neocortex and hippocampus. These consist of paired helical filaments (PHFs) on electron microscopy. Which of the following biochemical changes most likely accounts for the development of PHFs in this condition?

The activity of which of the following enzymes is directly affected by citrate?

Which of the following structures is found only in Gram-negative microorganisms?

A scientist wishes to study free radical production under ischemic conditions. He decides to produce cerebral ischemia by tying off an artery of the brain. Ligation of which of the following arteries would be most likely to produce significant ischemic damage?

Most fascia of the body that attach to bones attach by which of the following mechanisms?

A 52-year-old woman has long-standing rheumatoid arthritis (RA) and is being treated with corticosteroids and nonsteroidal anti-inflammatory drugs (NSAIDs). Which of the following cardiac complications may arise in this clinical setting?