Blood Supply

Blood Supply to the Brain

  • Circle of Willis

    • A circulatory structure at the base of the brain.

  • Basilar Artery

    • Formed by the union of the vertebral arteries.

    • Supplies the brainstem and cerebellum.

    • Provides branches such as the Rostral Cerebellar Artery.

  • Internal Carotid Arteries

    • Supply blood to the anterior part of the brain.

    • Give off the Middle Cerebral Artery.

  • Arterial Contributions

    • Basilar (20% of blood supply).

    • Internal Carotid (80% of blood supply).

  • Ischemic Strokes

    • Occurs when blood clots block these arteries.

    • Most significant in canine species.

    • Mentioned percentages of ischemic strokes relevant to each artery: 40-50%.

  • Importance of Arterial Supply

    • Supplies oxygen and nutrients needed by the brain.

    • Highlights the role of cerebral blood flow in brain function.

Venous System of the Brain

  • Function

    • Drains waste products from brain tissue.

  • Major Venous Sinuses

    • Dorsal Sagittal Sinus

    • Drains both hemispheres of the brain.

    • Located between the two cerebral hemispheres.

    • Straight Sinus

    • Receives blood from the dorsal sagittal sinus.

    • Transverse Sinuses

    • Runs laterally, draining blood from the straight sinus.

      • Embraces both sides of the cerebral hemispheres.

    • Sigmoid Sinuses

    • Continuation of the transverse sinuses, they drain into the internal jugular vein.

    • Petrosal Sinus

    • Drains venous blood from certain areas of the brain.

    • Cavernous Sinus

    • Acts in regulating the temperature of arterial blood.@

  • Sinus Drainage

    • Venous blood from the dorsal sagittal, straight, and transverse sinuses flows into the internal jugular veins.

    • Cleansing of brain tissue must be done via this venous system.

Cerebrospinal Fluid (CSF)

  • Production Site

    • Produced in the Choroid Plexus within all ventricles (two laterals, one third, one fourth).

  • Function

    • Provides buoyancy, protection, and nourishment to the CNS.

  • Flow of CSF

    • Begins at the choroid plexus in the lateral ventricles.

    • Flows to the third ventricle via the foramen of Monro.

    • Enters the fourth ventricle through the Sylvian aqueduct.

    • Exits to the subarachnoid space.

  • Accumulation Issues

    • Can lead to Hydrocephalus if blockages occur in the flow of CSF.

  • Characteristics of CSF

    • Clear, colorless fluid, ultrafiltrate of blood without red blood cells, and containing glucose, electrolytes, and nutrients.

    • Increased protein levels in CSF can indicate disease (e.g., meningitis).

Meninges

  • Layers of Meninges

    • Dura Mater (Outer layer):

    • Composed of periosteal and meningeal layers.

    • Contains potential spaces (epidural, subdural).

    • Arachnoid Mater

    • Contains subarachnoid space, which houses CSF.

    • Pia Mater (Inner layer):

    • Closely envelops the brain.

  • Areas Lacking Meninges

    • Falx Cerebri: Separates the two hemispheres.

    • Tentorium Cerebelli: Separates cerebrum from cerebellum.

    • Filum Terminale: Terminal part of the spinal cord.

Blood-Brain Barrier (BBB)

  • Function

    • Protects the brain from harmful substances while allowing essential nutrients to pass through.

  • Composition

    • Endothelial cells with tight junctions.

    • Supported by astrocytes' foot processes.

  • Areas Lacking BBB

    • The Area Postrema: Involved in the vomiting reflex.

    • Aortic Arch: Contains baroreception for blood pressure monitoring.

    • Posterior Pituitary: Releases hormones such as oxytocin and vasopressin directly into the circulation.