COMLEX-USA Biomedical Sciences 3

Question 1

Which structure in the nephron is primarily responsible for concentrating urine through countercurrent multiplication?

Accepted Answer

Loop of Henle

Answer

The loop of Henle creates a hyperosmotic medullary gradient via countercurrent multiplication, enabling the collecting duct to concentrate urine.

Question 2

Wernicke's area, responsible for language comprehension, is located in which brain region?

Accepted Answer

Superior temporal gyrus, dominant hemisphere

Answer

Wernicke's area is in the posterior superior temporal gyrus of the dominant hemisphere and is critical for language comprehension.

Question 3

A missense mutation results in:

Accepted Answer

A single amino acid substitution

Answer

A missense mutation changes a single nucleotide such that it codes for a different amino acid, potentially altering protein function.

Question 4

The bile salt-independent fraction of bile secretion is driven primarily by which mechanism?

Accepted Answer

Bicarbonate secretion by cholangiocytes

Answer

Cholangiocytes secrete bicarbonate via CFTR and AE2 exchangers, driving water flow and contributing to the bile salt-independent fraction of bile.

Question 5

Which cranial nerve is responsible for the afferent limb of the corneal reflex?

Accepted Answer

CN V1 (ophthalmic branch of trigeminal)

Answer

The ophthalmic branch (V1) of the trigeminal nerve carries sensory input from the cornea as the afferent limb of the corneal reflex.

COMLEX-USA Practice Test