Cerebral Blood Supply and Edema

Blood Supply to the Brain

• Blood is supplied to the brain by 2 carotid arteries (80%) and 2 intervertebral arteries (20%)
• These arteries form a redundant circulatory loop that spreads over the brain cortices, entering the tissue from the parenchyma perpendicular to the brain surface
• Cerebral edema (swelling) compresses the vasculature against the skull, impairing perfusion and causing widespread hypoxia
• The extent of hypoxia and damage depends on collateral circulation from unaffected areas

Cerebral Spinal Fluid (CSF)

• CSF is a ~125-150 mL fluid surrounding the brain and spinal cord
• CSF fills the "open" spaces within the Central Nervous System (CNS)
• CSF is produced by choroid plexus cells in CNS ventricles at a rate of ~500 mL/day, with constant turnover
• CSF drains into the venous and meningeal lymphatic system

Functions of CSF

• Buoyancy: provides support to the brain and spinal cord
• Protection: acts as a shock absorber and protects the CNS from mechanical injuries
• Chemical stability: helps maintain a stable pH and removes waste products
• Creates pressure gradient that facilitates perfusion

Composition of CSF

• Contains proteins (albumin, antibodies) and cells common in the periphery but not found in the CNS tissue
• Sampling CSF can provide clues about what's happening in the CNS tissue

Ependymal Cells

• Specialized epithelial cells that form a barrier between CSF and CNS
• Allow for the transfer of nutrients and components from CSF into the brain