A 24-year-old man comes to the office due to 2 days of pain in his left testis.  He has no significant medical history and takes no medications.  The patient has no known drug allergies.  Temperature is 37.1 C (98.8 F).  Physical examination reveals urethral discharge and an enlarged and tender left testis.  There is no inguinal lymphadenopathy.  A sample of the discharge is obtained by urethral swab.  Light microscopy of a Gram stain specimen reveals numerous neutrophils but no organisms.  HIV testing is negative.  Which of the following antimicrobial agents is most likely to improve this patient’s condition?

A 43-year-old man comes to the office due to headache, nausea, and stiff neck.  He has a history of a sexually transmitted infection at 29 years of age but completed prescribed treatment at the time.  Vital signs are normal.  The patient is alert and awake.  Cerebrospinal fluid examination shows increased white blood cells and protein.  Gram stain is negative.  Rapid plasma reagin test for syphilis and a fluorescent treponemal antibody absorption (FTA-ABS) assay are reactive.  He is prescribed procaine penicillin G and probenecid.  The most likely reason for administering probenecid in this patient is to inhibit which of the following processes?

A 28-year-old woman comes to the office for preconception counseling.  The patient has epilepsy and has tried multiple antiseizure medications in the past, but her seizures are controlled only with phenytoin.  She has not had a seizure in more than a year.  The patient has no other chronic medical conditions and takes no other daily prescription medications.  She takes a prenatal vitamin and does not use tobacco, alcohol, or illicit drugs.  Vital signs are normal.  BMI is 24 kg/m².  Physical examination is unremarkable.  If the patient becomes pregnant, the fetus will be at increased risk for which of the following anomalies?

A 15-year-old girl is brought to the office for evaluation of hypertension.  The patient was recently seen at a local walk-in clinic for a school sports examination and was told her blood pressure was elevated.  Medical history is unremarkable and she takes no medications.  The patient has not undergone menarche.  Height is at the 30th percentile for age and weight is at the 50th percentile.  Blood pressure is 155/95 mm Hg and pulse is 85/min.  Cardiovascular examination is normal and the thyroid is not enlarged.  Laboratory evaluation is notable for moderate hypokalemia but serum electrolytes, complete blood count, and thyroid studies are normal.  Follow-up testing reveals low daily urinary cortisol excretion.  Cortisol supplementation normalizes her blood pressure.  Which of the following steps in corticosteroid synthesis is most likely deficient in this patient?

A 65-year-old man has a 40-pack-year smoking history.  He has tried to quit several times but has never succeeded.  He has a chronic cough accompanied by scanty sputum production in the morning.  During one of his morning coughing episodes, he loses consciousness for approximately a minute.  Which of the following most likely contributed to syncope in this patient?

A 6-year-old boy is undergoing a genetic study after developing several tumors.  Skin biopsy is performed and fibroblasts are extracted from the tissue sample.  Fibroblasts from a healthy volunteer are also obtained.  The cells from both subjects are exposed to certain environmental factors and subsequently incubated in a growth medium.  After several hours, DNA is extracted from both cells and treated with an endonuclease that selectively cleaves DNA near sites of covalently bound adjacent pyrimidine bases.  The enzyme cleaves the patient’s DNA at numerous sites whereas the healthy volunteer’s DNA remains un-fragmented.  This patient most likely suffers from which of the following conditions?

A 45-year-old man comes to the office due to a neck mass.  He first noticed the mass 9 months ago.  Physical examination reveals submandibular lymphadenopathy on the right.  The enlarged lymph nodes are firm, movable, and nontender.  Biopsy demonstrates nodules that contain small lymphoid cells with cleaved nuclei that overexpress BCL2 protein.  Which of the following is the most likely diagnosis?

A 46-year-old homeless male presents to the emergency department with progressive fatigue and poor appetite.  He has lost 7 pounds over the last month.  Physical examination reveals yellowish sclerae and abdominal swelling.  Several small skin lesions are seen on his trunk, face and upper arms.  The lesions are red in color and contain multiple dilated blood vessels radiating from a single central vessel under close inspection.  This latter finding is most suggestive of which of the following?

A 51-year-old man comes to the outpatient clinic to initiate medical care.  He has a long history of flesh-colored skin nodules on his neck and back.  The lesions have been present for years and involve an extensive area.  His past medical history is significant for a brain tumor that was resected in childhood.  The patient has also been seen frequently for intermittent low back pain.  Vital signs are normal.  On skin examination, the patient has multiple freckles, nodules, and pigmented lesions at the inner aspect of the arm, axilla, and trunk.  Physical examination also shows mild scoliosis.  The skin nodules in this patient most likely result from excessive proliferation of which of the following cell types?

In a sample of 500 apparently healthy students, the blood glucose level seems to be normally distributed with a mean of 90 mg/dL and a standard deviation of 5 mg/dL (see curve below).

What is the percentage of students with blood glucose values in the shaded area under the curve?

A 22-year-old woman comes to the clinic due to worsening pelvic pain over the past 2 years.  The pain begins 3 days prior to menses, continues through menstruation, and resolves at the end of the menstrual period.  The patient is a university student and has missed class due to the symptoms.  Menarche was at age 10.  Menses occur every 27 days and last 5-7 days.  Nonsteroidal anti-inflammatory drugs provide minimal relief from the pelvic pain.  Physical examination is normal.  During laparoscopy, thin, filmy adhesions are noted throughout the pelvis; nodular implants are also noted in the posterior cul-de-sac and throughout the uterosacral ligaments.  Several blue papules are found on the bladder, and a 4-cm mass is seen on the right ovary.  If this condition is left untreated, this patient is at increased risk of which of the following complications?

A 31-year-old man comes to the office due to abdominal cramping and diarrhea, which started a few months ago and have gotten progressively worse.  The patient has recently noticed blood in his stool.  He was diagnosed with HIV six years ago, and his CD4 count two weeks ago was 360/mm³.  Sigmoidoscopy demonstrates friable, inflamed mucosa in the rectum and sigmoid colon.  Biopsies from these areas show collections of neutrophils in the crypt lumina.  Which of the following is the most likely diagnosis?

A 38-year-old woman, gravida 2 para 2, comes to the office due to amenorrhea.  Menses began at age 13 and previously occurred monthly.  She typically had light bleeding that lasted 3-4 days with no pain or cramping.  Over the past 18 months, the patient has had irregular menses and her last menstrual period was 6 months ago.  In addition, she has had vaginal dryness that has made intercourse uncomfortable.  Medical history is significant for acute lymphoblastic leukemia when she was an adolescent, which was treated with chemotherapy.  Laboratory results are as follows:

Which of the following ovarian processes is the most likely cause of this patient’s amenorrhea?

A new test is devised that uses latex particles coated with β-hCG.  A woman adds her urine into a glass containing anti-hCG antibodies.  Once she adds the reagent containing the latex particles to the urine, she observes agglutination.  Which of the following is the most accurate statement about the test results?

A 72-year-old man returns to the office a week after starting a new medication for his psychiatric symptoms.  During the past 3 months, the patient has had trials of 2 other medications that were discontinued due to poor response.  He continues to have poor sleep, poor appetite, weight loss, low motivation, low energy, and sad mood.  The patient has no prior history of psychiatric symptoms or disorders.  His past medical history is significant for migraines, diabetes mellitus, and benign prostatic hyperplasia.  He takes no other psychiatric medications.  The patient says that since starting the new medication he has had fewer bowel movements and difficulty with urination.  He also becomes dizzy when he stands up too quickly and his heart seems to race at times.  Which of the following medications is most likely to cause these new side effects?

A 7-year-old intellectually disabled boy is brought to the office for routine evaluation.  The patient’s mother reports that he is stubborn and throws frequent temper tantrums.  His weight is in the 95th percentile.  Physical examination shows dysmorphic facial features.  Genetic testing is performed on blood samples obtained from the patient and his parents.  Chromosome 15 DNA is then isolated and exposed to restriction enzymes.  The resulting DNA fragments are separated by gel electrophoresis and hybridized with a probe complementary to the DNA sequence of interest.

Which of the following best explains the observed results?

A 49-year-old man comes to the emergency department due to chest pain.  The patient describes substernal burning pain for the last 3 hours.  He has a history of hypertension and diet-controlled type 2 diabetes mellitus.  His father died of a stroke at age 60.  ECG shows normal sinus rhythm with 1 mm horizontal ST segment depression in the inferior leads.  Coronary angiogram shows 95% narrowing of the right coronary artery.  A stent is successfully placed in the culprit vessel with marked improvement in blood flow following the procedure.  The stent is coated with everolimus, a semi-synthetic lipophilic derivate of sirolimus.  Which of the following best describes the purpose of this drug coating?

A 23-year-old man comes to the office due to 3 days of fever, myalgia, nasal congestion, and sore throat.  He has had some symptom relief with over-the-counter acetaminophen.  Temperature is 38.3 C (101 F), blood pressure is 110/70 mm Hg, pulse is 98/min, and respirations are 18/min.  Physical examination shows clear nasal discharge and pharyngeal erythema.  The lungs are clear on auscultation.  Molecular assay of a nasopharyngeal swab detects a single-stranded RNA viral genome.  Ribonucleoproteins of this virus have a nuclear localization signal that facilitates entry into the host nucleus for genome replication.  Which of the following is the most likely causal organism?

A 14-year-old girl comes to the emergency department with right shoulder pain after a motor vehicle collision.  The patient was a restrained passenger when the car was struck from the opposite side, throwing her into the door.  She has no head injury and experienced no loss of consciousness after the collision.  Vital signs are normal.  Examination reveals tenderness and swelling in the right shoulder area.  The patient feels significant pain with any motion of the shoulder.  An x-ray of the right shoulder is shown in the image below.

Tension from which of the following muscles is most likely causing displacement of the proximal portion of the fractured bone?

A 24-year-old woman comes to the office due to numbness and pain in the right lower extremity.  The patient is upset because the symptoms interfere with her ballet class.  She has a history of chronic back pain after a work-related injury but has no other medical conditions.  The patient works in a chemical factory, where she is required to wear knee-high boots.  On physical examination, there is decreased sensation along the lateral right lower leg and dorsal right foot, and the patient is unable to walk on her heels.  Patellar tendon reflexes are 2+ and symmetric bilaterally.  Dysfunction of which of the following nerves is the most likely cause of this patient’s symptoms?

A pharmaceutical researcher is studying the structure and function of a cellular receptor that is targeted by a novel chemotherapeutic agent.  The target receptors, which are located on the membranes of cancer cells, are isolated and purified.  X-ray crystallography of these receptors reveals a large protein with 7 membrane-spanning helical domains composed mainly of hydrophobic amino acids.  Which of the following is most likely to be immediately activated on ligand binding to these receptors?

A 2-day-old boy is admitted to the intensive care unit due to poor feeding, occasional emesis, and progressive lethargy and seizures over the past day.  He was born at term via spontaneous vaginal delivery, and his mother had appropriate prenatal care.  Family history is not significant.  Temperature is 36.7 C (98 F), blood pressure is 70/30 mm Hg, pulse is 124/min, and respirations are 60/min.  Neurological examination reveals a lethargic patient with severe hypotonia.  Laboratory evaluation shows normal blood glucose, a high ammonium level, and increased urinary orotic acid excretion.  Imaging of the head reveals cerebral edema.  Which of the following enzymes is most likely deficient in this patient?

A research scientist is studying factors that are necessary for normal collagen synthesis and function.  He performs an animal experiment in which adult mice are divided into 2 groups; one group receives a diet containing a prolyl hydroxylase inhibitor, whereas the second group serves as a control and receives a diet lacking the inhibitor.  After several weeks, histochemical analysis is performed on tissues obtained from both groups.  Which of the following is most likely to be observed in the experimental group compared to the control?

A microbiologist is researching the use of a bacteriophage virus in the treatment of vancomycin-resistant Enterococcus faecalis infection.  The phage virus used in the experiment is capable of lytic infection only, whereby bacterial cells infected with the virus are lysed following replication of the virion.  Once the virus penetrates the bacterial cell, it takes over the bacterial machinery and uses it to replicate its own genetic material separately from the host DNA.  During the process, bacterial DNA fragments are packed into structurally normal virions in place of phage DNA.  The abnormal bacteriophages are most likely to have which of the following characteristics?

A 24-year-old man is brought to the emergency department after a motor vehicle collision.  The patient was sitting unrestrained in the driver’s seat when his car collided with a tree.  MRI of the head 12 hours afterward shows displacement of the innermost portion of the right temporal lobe under the tentorium cerebelli.  Which of the following structures is most likely to be impaired in this patient given his imaging findings?

A 28-year-old woman comes to the emergency department with nausea, dizziness, and abdominal pain.  The patient states, “If I didn’t have this pain everything would be okay.”  She tearfully reports that over the past year numerous doctors have been unable to help her.  She appears to have significant anxiety about the state of her health and how no one can help her.  The patient has been eating poorly due to abdominal pain and nausea and has lost 2.27 kg (5 lb).  She has also had a headache and low back and neck pain that have persisted despite high doses of analgesics, which she has recently stopped taking.  Her chronic pain prevents her from participating in most activities, and her boyfriend recently broke up with her because of this.  Physical examination, complete blood count, and serum chemistries are normal.  Toxicology screen is negative.  Which of the following is the most likely cause of this patient’s condition?

A genetic study is being performed on a 21-year-old man after his father dies from a progressive neurodegenerative condition.  The patient himself has no symptoms, but his father had a gradual decline of functional abilities over the past decade and died at age 53 due to complications of pneumonia.  Postmortem analysis of the father’s brain tissue reveals a neuronal protein containing long runs of extra glutamine residues located near the amino terminal.  Genetic testing of the patient shows a chromosomal abnormality that is similar to his father’s, but testing of the mother is normal.  Which of the following genetic phenomena is most likely to be seen in this patient?

A 64-year-old woman comes to the emergency department due to sudden onset of severe lower back pain.  The pain began after she landed with moderate force on a chair that was several inches lower than she expected.  The patient rates the pain as 8 on a scale of 0-10.  Medical history is significant for occasional heartburn and tension headaches responsive to over-the-counter medications.  She has no known drug allergies and does not use tobacco, alcohol, or illicit drugs.  The patient works as a salesperson in a department store.  Temperature is 36.7 C (98 F), blood pressure is 120/70 mm Hg, and pulse is 110/min.  BMI is 19 kg/m².  On physical examination, there is focal midline tenderness over the T12 vertebra.  Neurological examination shows no abnormalities.  Decreased function of which of the following organs most likely contributed to her condition?

A 61-year-old man is brought to the office by his daughter for evaluation of memory impairment that she first noticed 3 months ago.  The daughter states that the patient cannot remember the content of conversations almost immediately after they have finished, but his memories of events from childhood are intact.  The patient is asked how he got to the office.  He replies, “I got in the car, drove for 2 hours, and then hopped on a trolley.”  The daughter says, “He lives 10 minutes away from here and I picked him up in my car.  I don’t understand why he keeps making stuff up.”  The patient appears indifferent to his daughter’s concerns and does not believe there is anything wrong with him.  Medical history includes hypertension, hyperlipidemia, and multiple hospitalizations for delirium tremens.  Blood pressure is 137/85 mm Hg and pulse is 78/min.  Gait is wide based and steady.  The patient recalls 0 of 3 items after 5 minutes but confidently names 3 inaccurate items.  Which of the following is the most likely cause of this patient’s cognitive impairment?

A 15-year-old girl is brought to the clinic due to primary amenorrhea.  She has had no development of secondary sexual characteristics and has not experienced an adolescent growth spurt.  The patient is physically active and feels well.  She has no chronic medical conditions and takes no medications.  Blood pressure is 156/95 mm Hg and heart rate is 78/min.  Height is 155 cm (61 in).  BMI is normal.  On examination, there is no pubic or axillary hair and no breast development.  Examination is otherwise unremarkable.  Laboratory evaluation confirms a defect in the steroid hormone synthesis pathway as depicted below (X denotes block in the pathway).

Which of the following changes in serum hormone levels are most likely to be seen in this patient?

A 2-year-old boy is brought to the emergency department with lethargy and seizures.  His parents say that he has had a “stomach virus” for the last 3 days and has not been able to keep any food down.  Physical examination shows hepatomegaly.  Serum laboratory studies show severe hypoglycemia, low ketone levels, and elevated levels of octanoylcarnitine.  Further evaluation confirms the diagnosis of medium-chain acyl-coenzyme A dehydrogenase (MCAD) deficiency.  Separate DNA samples are obtained from the patient and his family members, and the MCAD genes in each sample are isolated and amplified using a polymerase chain reaction technique.  The samples are then treated with a restriction endonuclease and analyzed using gel electrophoresis.  The results are shown below.

Which of the following statements is the best interpretation of the above findings?

A 36-year-old man is referred for genetic testing by his primary care physician.  Evaluation reveals a germline mutation in a gene involved in DNA replication.  Specifically, the mutation causes loss of function of a protein that helps detect and correct base pair errors in microsatellites, short DNA sequences composed of repetitive stretches of nucleotides.  This patient will most likely develop which of the following conditions as a result of the mutation?

A 34-year-old man with a history of intravenous drug use comes to the hospital due to 4 weeks of progressive low back pain that worsens with activity.  The patient also has had malaise, fatigue, and night sweats for the past several weeks.  He has no lower extremity weakness, numbness, or bladder/bowel dysfunction.  His past medical history is unremarkable except for multiple episodes of cellulitis that required treatment with intravenous antibiotics.  The patient’s temperature is 37.7 C (100 F).  There is diffuse lumbar midline and paraspinal muscle tenderness.  His leukocyte count is 18,000/mm³, and imaging studies reveal L1 to L3 vertebral osteomyelitis and discitis with psoas muscle inflammation.  HIV test is positive.  A bone biopsy of the affected lumbar bones is performed, and cultures grow acid-fast bacteria.  If these organisms spread along the psoas major muscle by direct extension, this patient is at greatest risk for developing an abscess in which of the following sites?

A 32-year-old man comes to the office due to a skin rash.  For the last 3 days, he has had an erythematous rash on his trunk associated with “prickly” or burning pain.  The patient has had similar outbreaks over the last 2 years in a variety of locations.  Some of the episodes were associated with a transient mild fever, but all resolved spontaneously.  Past medical history is notable for chronic back pain and fibromyalgia.  The patient works as a marketing manager and frequently travels for his job.  He smokes 5 cigarettes a day, along with variable alcohol intake and regular use of marijuana on weekends.  Physical examination findings are shown in the image below.

Which of the following infections may have predisposed the patient to development of this rash?

A 56-year-old man comes to the clinic due to progressive shortness of breath and leg swelling for the last several months.  He is also unable to sleep lying flat at night and has been using 2 pillows to avoid becoming short of breath.  Transthoracic echocardiogram shows a left ventricular ejection fraction of 34%.  Therapy with sacubitril-valsartan is initiated.  Which of the following hormonal changes are expected in this patient as a result of this therapy?

Researchers investigating an outbreak of a newly discovered virus isolate a specific viral gene that codes for a protein responsible for mediating viral entry into respiratory mucosal cells.  A recombinant version of the protein is manufactured in the laboratory with the goal of generating an effective vaccine.  When the recombinant protein is injected into healthy adult volunteers, researchers find that individuals with particular human leukocyte antigen haplotypes do not mount an effective IgG antibody response against the antigen.  These subjects are most likely to have a primary defect involving which of the following processes?

A 67-year-old woman comes to the office due to pain and stiffness in her hands and fingers.  Her symptoms started 6 months ago and have worsened progressively, to the degree that she has had to limit her activities.  Opening jars and turning doorknobs are particularly painful.  Past medical history is notable for hypertension and hypothyroidism, for which she takes the appropriate medications.  The patient does not use tobacco and drinks alcohol only occasionally.  An x-ray of her wrist and hand joints is shown in the image below.

Which of the following is the most likely cause of this patient’s symptoms?

A 38-year-old man with a history of mild, intermittent asthma comes to the outpatient clinic due to 2 days of fever, cough, right-sided chest pain, and malaise.  He states that his coworkers have been sick and he believes that he “caught the flu.”  The patient is instructed in symptomatic measures and sent home.  Three days later, he is brought to the emergency department with progressive lethargy and shortness of breath.  Temperature is 40 C (104 F), blood pressure is 102/80 mm Hg, and pulse is 103/min with a regular rhythm.  Chest x-ray reveals diffuse bilateral lung opacities.  Arterial blood gas analysis on 40% supplemental oxygen shows the following:

Which of the following is the most likely cause of this patient’s decreased oxygen saturation?