1 Chapter 17: Blood Supply Chris Rorden University of South Carolina Norman J. Arnold School of Public Health Department of Communication Sciences and Disorders University of South Carolina

2 Role of Blood Supply Nutrition to parenchyma (functional parts of organ = brain cells). –Brain is completely dependent on oxygen supply - No O2 reserves. Irreversible damage in 4-6 minutes if no oxygen Brain requires 20% of O2 for 2% of body weight. –Brain requires glucose for energy No ability to use fat Remove carbon dioxide and waste-products from cells Cerebral perfusion –> 60 ml/100gr min-1 in Gray matter –40 < X < 60 in White matter –750mL blood pumped per minute and circulated blood returned for reoxygenation

3 Vascular Network Network of arteries and veins –Arteries carry blood away from the heart –Arteries divide into smaller vessels called: arterioles –Arterioles divide further into capillaries Vascular Network –Veins carry blood toward the heart –Smallest level are venules that are connected to capillaries –Venules Carry blood to sinuses on cortical surface

4 Local blood flow Arteries Arterioles Capillaries Venules Sinuses

5 Cerebrovascular Supply Two Systems –Carotid System –Vertebral Basilar System Meet in Circle of Willis

6 Vertebral / Basilar Arteries Brain stem –Basilar Artery –Vertebral Arteries

7 Vertebral Basilar System Two Vertebral Arteries enter skull through Foramen Magnum Join to form the Basilar Artery and then Circle of Willis Numerous small branches Supplies the brainstem and cerebellum Cerebellum: Superior Cerebellar Artery Anterior Inferior Cerebellar Artery Posterior Inferior Cerebellar Artery

8 Carotid Arteries

9 Carotid System Common Carotid Artery Divides into two branches –External Branch Supply blood to facial muscles, forehead and oral, nasal and orbital cavities –Internal Branch (enters the skull through the carotid foramen) Anterior choroidal artery (supplies optic tract, posterior limb of internal capsule, branches to midbrain,and lateral geniculate nucleus). Ophthalmic artery (Supplies blood to the eyeball and ocular muscles) –Major source of blood to the brain –After joining Circle of Willis becomes anterior cerebral and middle cerebral arteries

10 Circle of Willis

11 Circle of Willis Wreath-shaped circle of Willis located at ventral surface of brain Connects Carotid and Vertebral Basilar Systems –Middle and Anterior Cerebral Arteries –Anterior Communicating Artery –Posterior Cerebral Artery –Posterior Communicating Artery

12 Cortical Blood Supply –ACA: Medial Frontal Perfusion –MCA: Lateral Perfusion –PCA: Posterior medial Perfusion, cerebellum –Watershed Areas: overlap between major arteries Major Arteries Carotid Anterior Cerebral Middle Cerebral Posterior Cerebral

13 Two Types of Arteries Cortical (Circumferential) Branches –Supply External Brain Structures Central (Penetrating) Branches –Small –Penetrate ventral surface to supply internal brain structures

14 Anterior Cerebral Artery Supplies Orbital and Medial Surfaces of Frontal and Parietal Lobes Interruption causes –Cortical Arteries –Paralysis of legs and feet –Difficulty in prefrontal lobe functions of cognitive thinking, judgment, motor initiation and self monitoring

15 Middle Cerebral Artery Direct continuation of carotid artery Cortical Branches –Temporal –Parietal –Frontal

16 MCA: Cortical Branches Supplies blood to entire lateral surface of brain –Somatosensory Cortex –Motor Cortex –Broca's Area –Heschl’s Gyrus –Wernicke’s Area Therefore, symptoms include –Aphasia –Motor deficits –Neglect (right hemisphere)

17 MCA – Penetrating Arteries Supplies basal ganglia and diencephalon Interruption causes –Contralateral hemiplegia –Impaired sensory systems –Touch –Pain and temperature

18 Central Penetrating Arteries Arise from cortical arteries or from Circle of Willis Penetrate inferior surface of brain Can form channels to facilitate blood supply Central (Penetrating) Arteries Supply –Thalamus –Hypothalamus –Basal Ganglia –Internal capsule –Choroid Plexus

19 Posterior Cerebral Artery Supplies blood to anterior and inferior temporal lobes, uncus, inferior temporal gyri, inferior and medial occipital lobe Watersheds with middle cerebral artery Interruption causes –Homonymous hemianopsia –Possible total blindness –Cerebellar symptoms

20 Collateral Circulation Redundant arteries provide alternative supply when primary supply is lost Small, normally closed arteries open up after occlusion, connecting two larger arteries or different parts of the same artery. Dependent on location and severity of blockage –Better collateral circulation if blockage is near main trunk –Better if blockage occurs gradually

21 Vascular Pathologies Occlusive (Something is blocked causing ischemia). 80% of strokes are ischemic –Embolism: object from another part of the body which travels through artery until it gets stuck. –Thrombosis: object originating within a blood vessel: local buildup of fatty substances usually at a bifurcation of artery, these can rupture leading to catastrophic blockage Hemorrhagic (Bleed). 20% of strokes are due to arteries rupturing.

22 Risk factor for ischemic stroke Atherosclerosis from reduced lumen due to lipids, calcium fatty particles etc. (‘Athera’ = porridge in Greek) A form of Arteriosclerosis: a general term describing any hardening (and loss of elasticity) of arteries. Leads to stenosis (narrowing) of the artery, gradually leading to insufficient blood supply Plaques can rupture, creating a thrombus in blood supply

23 Vascular Pathologies - Bleeds Hemorrhagic Bleeding from ruptured vessels Types –Intracerebral: More common in thalamus and basal ganglia –Subdural –Aneurysm Aneurysm

24 Haemorrhages 20% of strokes are bleeds Typically, due to ruptured aneurysm –An aneurysm is a sac-like protrusion of an artery caused by a weakened area within the vessel wall. –Introspectively, the worst headache of your life. – –Surgery to clip aneurysm can save patients life. CT of recent haemorrhage

25 Arteriovenous Malformations AVMs can cause hemorrhagic strokes Tangled web of arteries and veins present since birth ~3 percent of all AVMs hemorrhage

26 Venous Sinus System Blood returns to lungs for oxygen Drain into Sinus System Dural Sinuses –Superior Sagittal Sinus –Inferior Sagittal Sinus –Straight Sinus –Transverse Sinus –Cavernous Sinus –Petrosal Sinuses

27 Notes Regulation of Cerebral Blood Flow –Closed system under constant pressure –Controlled by elasticity of blood vessels, and metabolic needs –Aging can cause less elasticity responsiveness and eveness of flow Blood-Brain Barrier –Tight system does not allow direct contact of all brain tissues with blood –Specialized system to extract needed molecules –May impede medicine entering the brain