Mixed Deck — All USMLE Topics Flashcards

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Answer: 5α-reductase deficiency

5α-reductase deficiency is a disorder of sex development where testosterone cannot be converted to dihydrotestosterone (DHT). DHT is essential for the development of external male genitalia in utero. Individuals with this XY genetic makeup may present with ambiguous genitalia at birth, often virilizing at puberty due to increased testosterone.

Which ACE inhibitor side effect is class-specific and due to bradykinin accumulation?

Answer: Dry cough

ACE inhibitors prevent bradykinin degradation, causing dry cough in up to 15% of patients; ARBs do not inhibit bradykinin breakdown and lack this side effect.

The sinoatrial (SA) node receives its arterial supply from the SA nodal artery, which arises from which vessel in approximately 60% of individuals?

Answer: Right coronary artery

In approximately 60% of individuals, the SA nodal artery arises from the right coronary artery; in the remaining ~40%, it arises from the left circumflex artery.

Which drug is a selective serotonin reuptake inhibitor (SSRI) with the longest half-life and is used to minimize withdrawal syndrome?

Answer: Fluoxetine

Fluoxetine has the longest half-life (~1-4 days) among SSRIs due to its active metabolite norfluoxetine, making discontinuation syndrome rare.

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Answer: Rathke’s pouch

Rathke's pouch is an ectodermal invagination from the roof of the primitive oral cavity that gives rise to the anterior pituitary gland (adenohypophysis). Craniopharyngiomas are tumors that arise from remnants of Rathke's pouch. These tumors are typically suprasellar and can cause symptoms due to compression of surrounding structures like the optic chiasm or hypothalamus, often leading to endocrine dysfunction.

Which mechanism explains why aminoglycosides are bactericidal despite being protein synthesis inhibitors?

Answer: They cause misreading of mRNA, producing abnormal proteins that disrupt cell membranes

Aminoglycosides cause misreading at the 30S ribosome, incorporating wrong amino acids that create aberrant proteins which disrupt the cell membrane, causing bactericidal cell death.

Which hepatitis virus uses RNA-dependent RNA polymerase and requires co-infection with hepatitis B virus for replication?

Answer: Hepatitis D (HDV)

Hepatitis D (delta virus) is a defective RNA virus that requires HBV surface antigen (HBsAg) for encapsidation, and can only infect HBV-positive patients (co- or superinfection).

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Answer: Creatinine clearance

Creatinine clearance is the most commonly used clinical measure to estimate the glomerular filtration rate (GFR), which reflects overall kidney function. It quantifies the volume of blood plasma cleared of creatinine per unit time. This provides a practical and relatively accurate assessment of how well the kidneys are filtering waste products from the blood.

A patient has a Cushing reflex (hypertension, bradycardia, and irregular respirations). What does this indicate?

Answer: Increased intracranial pressure threatening brainstem herniation

The Cushing reflex is a late sign of severely elevated ICP causing brainstem ischemia; the hypertension is a compensatory response to maintain cerebral perfusion against rising ICP.

A patient has syndrome of inappropriate antidiuretic hormone (SIADH). What is the expected urine osmolality?

Answer: High urine osmolality (>100 mOsm/kg)

In SIADH, excess ADH causes inappropriate water retention and concentrated urine (>100 mOsm/kg, often >300 mOsm/kg) despite low serum osmolality.

Which diuretic acts on the thick ascending limb of the loop of Henle and inhibits the Na-K-2Cl cotransporter?

Answer: Furosemide

Furosemide inhibits the Na-K-2Cl cotransporter in the thick ascending limb of the loop of Henle, producing powerful natriuresis and diuresis.

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Answer: Posterior deviation of the tracheoesophageal septum

Esophageal atresia with tracheoesophageal fistula (TEF) is a congenital anomaly resulting from incomplete separation of the foregut into the esophagus and trachea during embryonic development. This occurs due to abnormal posterior deviation of the tracheoesophageal septum, leading to a blind-ending esophagus and an abnormal connection between the trachea and esophagus.

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Answer: "Doctor, you must be wrong."

This question likely refers to Kübler-Ross's stages of grief. 'Doctor, you must be wrong' represents the stage of denial, which is typically the first reaction to receiving a devastating diagnosis. In this stage, individuals struggle to accept the reality of their situation.

A patient with SLE has a positive ANA and anti-dsDNA antibodies. Which type of hypersensitivity reaction mediates the kidney damage in lupus nephritis?

Answer: Type III (immune complex-mediated)

Lupus nephritis is caused by deposition of immune complexes (dsDNA-anti-dsDNA) in the glomerular basement membrane, activating complement and causing type III hypersensitivity injury.

Which finding on renal biopsy is pathognomonic for Goodpasture syndrome?

Answer: Linear IgG deposits along the glomerular basement membrane

Goodpasture syndrome shows linear IgG deposits along the GBM on immunofluorescence due to anti-GBM antibodies targeting type IV collagen (alpha-3 chain).

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Answer: Panacinar

Panacinar emphysema, also known as panlobular emphysema, is a type of chronic obstructive pulmonary disease (COPD) characterized by the destruction of the entire acinus, from the respiratory bronchioles to the alveoli. This form of emphysema is strongly associated with alpha-1 antitrypsin deficiency. The widespread destruction of alveolar walls leads to enlarged airspaces and reduced gas exchange capacity throughout the lung.

A patient presents with rice-water stools and rapid dehydration. The causative organism produces a toxin that permanently activates adenylate cyclase. What organism is responsible?

Answer: Vibrio cholerae

Vibrio cholerae produces cholera toxin (CT) that ADP-ribosylates Gs-alpha, permanently activating adenylate cyclase and causing massive chloride secretion and profuse watery diarrhea.

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Answer: Pheochromocytoma

Pheochromocytoma is a tumor of the adrenal medulla that secretes excessive amounts of catecholamines (epinephrine and norepinephrine). This leads to classic symptoms such as episodic hypertension, palpitations, headaches, and sweating. It is important to diagnose and treat pheochromocytoma due to the risk of hypertensive crises and cardiovascular complications.

A patient with chronic myeloid leukemia (CML) has the Philadelphia chromosome. Which genetic translocation produces this?

Answer: t(9;22)

CML is characterized by t(9;22), creating the BCR-ABL fusion gene on the Philadelphia chromosome, which encodes a constitutively active tyrosine kinase.

Which vitamin is a cofactor for pyruvate dehydrogenase, alpha-ketoglutarate dehydrogenase, and transketolase?

Answer: Thiamine (B1)

Thiamine (B1) as thiamine pyrophosphate (TPP) is essential for pyruvate dehydrogenase, alpha-ketoglutarate dehydrogenase, and transketolase reactions.