How do arachnoid villi function?

How do arachnoid villi function?

• A. When CSF pressure is lower than venous sinus pressure, CSF is drawn into the venous blood.
• B. They actively secrete CSF.
• C. When CSF pressure exceeds venous sinus pressure, CSF is forced through the villi into the low-pressure venous blood.
• D. They store CSF.

Answer: (C)

Arachnoid villi act as one-way outlets that drain CSF from the subarachnoid space into the dural venous sinuses. They are not sites of CSF production or storage; production occurs in the choroid plexus, and CSF exits the system through these villi when the pressure in the CSF space exceeds the pressure in the venous sinuses. In other words, the flow is driven by the CSF pressure being higher than the venous pressure, pushing CSF into the low-pressure venous blood.

Arachnoid villi act as one-way outlets that drain CSF from the subarachnoid space into the dural venous sinuses. They are not sites of CSF production or storage; production occurs in the choroid plexus, and CSF exits the system through these villi when the pressure in the CSF space exceeds the pressure in the venous sinuses. In other words, the flow is driven by the CSF pressure being higher than the venous pressure, pushing CSF into the low-pressure venous blood.