Mixed Deck — All NBME Topics Flashcards

The cloacal membrane divides into the urogenital membrane and anal membrane at approximately which embryonic week?

Answer: Week 7

The urorectal septum divides the cloaca into the urogenital sinus and anorectal canal by the end of the 7th week, separating the urogenital and anal membranes.

During eukaryotic DNA replication, which enzyme complex synthesizes the RNA primer at origins of replication?

Answer: DNA polymerase alpha-primase complex

DNA polymerase alpha associates with primase to synthesize short RNA primers that provide the 3'-OH needed by replicative DNA polymerases.

A 20-year-old man is brought to the emergency department 1 hour after he was involved in a motorcycle collision. He was not wearing a helmet. Physical examination shows clear fluid dripping from the nose. X-rays show a fracture of the cribriform plate of the ethmoid bone. This patient is at greatest risk for impairment of which of the following senses?

Answer: Olfaction

The cribriform plate of the ethmoid bone is perforated by the olfactory nerve filaments (Cranial Nerve I), which transmit the sense of smell. A fracture in this area, as described, directly damages these delicate nerves. This damage leads to anosmia, or the loss of the sense of olfaction. The clear fluid dripping from the nose is cerebrospinal fluid (CSF rhinorrhea), indicating a breach of the meninges and a direct connection between the subarachnoid space and the nasal cavity, further confirming the severity of the injury to this region.

Two days after beginning primaquine for malaria prophylaxis, a 17-year-old African American boy is brought to the physician because of dark urine and yellowing of his eyes. His pulse is 88/min, respirations are 12/min, and blood pressure is 124/68 mm Hg. Examination shows scleral icterus and pale mucous membranes. His hemoglobin concentration is 10 g/dL. A blood smear shows erythrocyte fragments and Heinz bodies. Which of the following is the most likely explanation for these findings?

Answer: Deficiency of glucose 6-phosphate dehydrogenase

The patient's symptoms of dark urine and jaundice, along with anemia and the presence of erythrocyte fragments and Heinz bodies on a blood smear, indicate hemolytic anemia. This reaction, occurring after starting primaquine (an oxidant drug) in an African American male, is highly characteristic of glucose-6-phosphate dehydrogenase (G6PD) deficiency. G6PD is crucial for protecting red blood cells from oxidative stress, and its deficiency makes them vulnerable to oxidant-induced hemolysis.

A 36-year-old woman with hypertension well-controlled on lisinopril asks about contraception. Which method is CONTRAINDICATED in this patient?

Answer: Combined estrogen-progestin oral contraceptives

Combined oral contraceptives are contraindicated in women with hypertension due to increased risk of stroke and myocardial infarction, especially over age 35.

A disease has a prevalence of 50 per 1,000 and an incidence of 10 per 1,000 per year. What is the average disease duration?

Answer: 5 years

Using the steady-state formula Prevalence = Incidence × Duration: Duration = 50/10 = 5 years.

A 40-year-old woman with lupus has been on hydroxychloroquine for 5 years. Which monitoring study is most important to perform annually?

Answer: Ophthalmologic examination with visual field testing

Hydroxychloroquine can cause irreversible retinal toxicity that is dose- and duration-dependent, requiring annual ophthalmologic screening after 5 years.

A 16-month-old infant babbled at 6 months, began to mimic sounds at 10 months, and began to use a few recognizable words between 12 and 14 months. At 16 months, the child is continuing to use single words but is not using simple two-word phrases. For each child brought for a well-child examination, select the most likely diagnosis.

Answer: Normal language development

This 16-month-old infant's language development, including babbling at 6 months, mimicking sounds at 10 months, and using a few recognizable words between 12 and 14 months, is within the normal developmental range. While the child is not yet using two-word phrases, this milestone typically emerges between 18 and 24 months of age. Therefore, the child's language development is considered normal for their age.

Which study design provides the STRONGEST evidence for a causal relationship between an exposure and outcome?

Answer: Randomized controlled trial

Randomized controlled trials eliminate confounding through random assignment, providing the highest level of evidence for causality.

A 45-year-old woman is found to have adenocarcinoma of the left breast. Resection of the tumor is scheduled, and the physician also plans to obtain samples of the draining nodes. To find these nodes, a radiotracer is injected adjacent to the tumor and images are obtained. The first draining sentinel node in this patient is most likely found at which of the following locations?

Answer: Ipsilateral axilla

The primary lymphatic drainage for most of the breast, especially the lateral quadrants, is to the ipsilateral axillary lymph nodes. These are typically the first nodes to receive lymphatic flow from a breast tumor, making them the sentinel nodes for biopsy in breast cancer staging.

The white pulp of the spleen is organized around central arterioles and is primarily composed of which cell type?

Answer: T and B lymphocytes

White pulp consists of periarteriolar lymphatic sheaths (T cells) and lymphoid follicles (B cells), forming the immune compartment of the spleen.

A sexually active 37-year-old woman comes to the physician because of a 2-day history of pain in the area of her genitals. Pelvic examination shows shallow, small, extremely tender ulcers with red bases in the vulvar and vaginal regions. A Tzanck smear shows the presence of multinucleated giant cells. Which of the following infectious agents is the most likely cause of these findings?

Answer: Herpes simplex virus

The presence of shallow, small, extremely tender ulcers with red bases in the vulvar and vaginal regions is highly characteristic of genital herpes. The finding of multinucleated giant cells on a Tzanck smear is a classic cytological hallmark of herpes simplex virus (HSV) infection, confirming the viral etiology. HSV causes painful vesicular lesions that rupture to form ulcers, and the Tzanck smear helps differentiate it from other causes of genital ulcers.

A patient with familial hypercholesterolemia has markedly elevated LDL. The primary defect impairs which cellular process?

Answer: Receptor-mediated endocytosis of LDL particles

Familial hypercholesterolemia is caused by loss-of-function mutations in the LDL receptor, impairing endocytosis and clearance of circulating LDL.

A 7-year-old develops a malar rash, arthritis, and carditis 3 weeks after an untreated streptococcal pharyngitis. Which immunological mechanism is thought to cause the cardiac damage in acute rheumatic fever?

Answer: Molecular mimicry between streptococcal M protein and cardiac myosin

Antibodies against Group A Streptococcus M protein cross-react with cardiac myosin (molecular mimicry), leading to autoimmune damage of the mitral and aortic valves in rheumatic fever.

A 72-year-old diabetic man presents with altered mental status and fruity breath. ABG shows pH 7.18, pCO2 22, HCO3 8 mEq/L. Blood glucose is 520 mg/dL with urine ketones. What is the first priority in management?

Answer: IV normal saline fluid resuscitation

Aggressive IV fluid resuscitation with normal saline corrects dehydration and must precede insulin administration in DKA.

A 55-year-old man with chronic alcoholism presents with jaundice and hepatomegaly. Liver biopsy shows hepatocyte swelling with intracytoplasmic eosinophilic inclusions. What are these inclusions?

Answer: Mallory-Denk bodies

Mallory-Denk bodies are aggregates of intermediate filaments (cytokeratins) found in hepatocytes in alcoholic liver disease.

Which organism is responsible for gas gangrene and produces an alpha toxin (lecithinase) that destroys cell membranes by cleaving phospholipids?

Answer: Clostridium perfringens

Clostridium perfringens produces alpha toxin (a phospholipase C/lecithinase) that hydrolyzes phosphatidylcholine in cell membranes, causing myonecrosis and hemolysis.

A 25-year-old woman reports chronic feelings of emptiness, frantic efforts to avoid abandonment, and a history of self-cutting when upset. She has had three suicide attempts. What personality disorder best fits?

Answer: Borderline personality disorder

Borderline personality disorder is defined by unstable mood, identity, and relationships, chronic emptiness, fear of abandonment, self-harm, and impulsivity.

A 50-year-old man comes to the physician because of a cough productive of large quantities of mucus for 6 months. He has smoked 1 pack of cigarettes daily for 25 years. Which of the following cell types is the most likely cause of the increase in this patient’s secretion of mucus?

Answer: Goblet cells

Goblet cells are specialized epithelial cells found in the respiratory tract that are responsible for producing and secreting mucus. Chronic irritation from smoking, as seen in this patient with chronic bronchitis, causes hypertrophy and hyperplasia of these cells. This increase in goblet cell number and size leads to excessive mucus production, which is characteristic of a productive cough in chronic bronchitis. Columnar ciliated epithelial cells help move mucus, but goblet cells are the primary producers.

A patient with complete biliary obstruction would most likely develop deficiency of which vitamins?

Answer: Fat-soluble vitamins A, D, E, and K

Bile salts are required for micelle formation and absorption of fat-soluble vitamins (A, D, E, K); biliary obstruction prevents this, causing deficiencies and coagulopathy.