The presence of a barrier between the bloodstream and the brain is suggested by the observation that
A) all cells of the body are stained by a dye injected into the bloodstream.
B) injection of dye into the bloodstream stains all cells but those of the brain and spinal cord.
C) the gut is stained by a dye injected into the brain ventricles.
D) injection of dye into the spinal cord stains the cells of the gut.
E) injection of dye into the gut stains the cells of the spinal cord.

Question

Quizplus · Accepted Answer

The fact that injection of dye into the bloodstream stains all cells except those of the brain and spinal cord suggests that there is a barrier preventing the dye from entering the brain and spinal cord. This barrier is known as the blood-brain barrier. Option A is incorrect as it contradicts the observation. Option C, D and E are also incorrect as they do not provide evidence for the presence of a blood-brain barrier.

The Presence of a Barrier Between the Bloodstream and the Brain