What three factors are known to cause cerebral vasoconstriction?

Cerebral vasoconstriction is influenced by various systemic and environmental factors that regulate blood flow to the brain. Among these, hypertension, hypocarbia, and alkalosis are known to promote vasoconstriction within cerebral circulation.

Hypertension leads to increased systemic vascular resistance, which can result in compensatory constriction of cerebral vessels to maintain adequate cerebral perfusion pressure. This helps prevent elevated intracranial pressure and maintains blood flow equilibrium.

Hypocarbia, or low levels of carbon dioxide in the blood, causes a decrease in hydrogen ion concentration and an increase in blood pH (alkalosis). As carbon dioxide levels drop, cerebral vessels constrict in response to decreased acidity, aiming to reduce blood flow to prevent potential cerebral edema. This response is part of the body's mechanism to regulate pH and blood flow while reacting to changes in respiratory function.

Additionally, alkalosis itself can contribute to cerebral vasoconstriction due to the associated drop in carbon dioxide levels, reinforcing the vasoconstrictive effect.

In summary, the correct answer identifies factors that lead to vasoconstriction within cerebral circulation by directly influencing vascular tone and pH levels.