1. Cerebrospinal fluid is separated from the body by what is known as the blood-
ID: 54793 • Letter: 1
Question
1. Cerebrospinal fluid is separated from the body by what is known as the blood-brain barrier. Yet changes in arterial PCO2 cause a proportional response in cerebrospinal fluid PCO2. Why is this?
A. The cells forming the capillaries in the brain contain CO2 channels which allow CO2 into the CSF via diffusion.
B. The cells forming the capillaries in the brain contain CO2 channels which allow CO2 into the CSF via facilitated diffusion.
C. CO2 is actively transported into the CSF using ATPase pumps.
D. CO2 is not restricted by capillary barriers.
Explanation / Answer
1. Cerebrospinal fluid is separated from the body by what is known as the blood-brain barrier. Yet changes in arterial PCO2 cause a proportional response in cerebrospinal fluid PCO2. Why is this?
A. The cells forming the capillaries in the brain contain CO2 channels which allow CO2 into the CSF via diffusion.
for understanding:
Central chemoreceptors of the central nervous system, located on the ventrolateral medullary surface in the vicinity of the exit of the 9th and 10th cranial nerves, are sensitive to the pH of their environment.
These act to detect the changes in pH of nearby cerebral spinal fluid (CSF) that are indicative of altered oxygen or carbon dioxide concentrations available to brain tissues. An increase in carbon dioxide causes tension of the arteries, often resulting from increased CO2 intake (hypercapnia), indirectly causes the blood to become more acidic; the cerebral spinal fluid pH is closely comparable to plasma, as carbon dioxide easily diffuses across the blood/brain barrier.
However, a change in plasma pH alone will not stimulate central chemoreceptors as H+ are not able to diffuse across the blood–brain barrier into the CSF. Only CO2 levels affect this as it can diffuse across, reacting with H2O to form carbonic acid and thus decrease pH. Central chemoreception remains, in this way, distinct from peripheral chemoreceptors.
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