Cerebral Blood Flow and ICP Overview
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Questions and Answers

What is the primary pathway for radicular veins to drain blood from the spinal cord?

  • Into the internal vertebral venous plexus (correct)
  • Through the subclavian vein
  • Directly into the jugular vein
  • Via the anterior spinal artery

    • According to the Monro-Kellie Doctrine, what is the relationship between the components of the cranial cavity?

  • Any volume change must be compensated by a displacement or replacement of another component. (correct)
  • An increase in one component does not change intracranial pressure.
  • Increased brain tissue volume directly leads to increased cerebrospinal fluid volume.
  • They are independent and do not affect each other.

    • Which condition is NOT typically associated with increased intracranial pressure (ICP)?

  • Neck stiffness
  • Severe headache
  • Papilledema
  • Bradycardia (correct)

    • What effect does an increase in CO2 levels have on cerebral blood flow?

    <p>It increases cerebral blood flow through vasodilation.</p> Signup and view all the answers

    What mechanism primarily controls blood circulation in the brain?

    <p>Local metabolic factors and brain tissue itself</p> Signup and view all the answers

    Which of the following is a consequence of increased intracranial pressure?

    <p>Herniation of cranial contents</p> Signup and view all the answers

    Which metabolites are involved in the local regulation of cerebral blood flow during increased activity?

    <p>H+, K+, CO2, O2, and adenosine</p> Signup and view all the answers

    Which option best describes the consequences of hypocapnia on cerebral blood flow?

    <p>It decreases cerebral blood flow due to vasoconstriction.</p> Signup and view all the answers

    Which structure primarily receives blood via the internal carotid artery?

    <p>Cerebrum</p> Signup and view all the answers

    What is the primary venous drainage system of the spinal cord?

    <p>Internal venous plexus</p> Signup and view all the answers

    How does the Monro-Kellie doctrine relate to intracranial pressure?

    <p>It indicates that intracranial pressure increases when there is an increase in one of the components.</p> Signup and view all the answers

    Which factor is NOT involved in the regulation of cerebral blood flow?

    <p>Venous return</p> Signup and view all the answers

    What effect does increased intracranial pressure typically have on cerebral blood flow?

    <p>Decreases cerebral blood flow due to reduced perfusion pressure.</p> Signup and view all the answers

    What is the primary function of venous sinuses in the brain?

    <p>To drain cerebral veins into the internal jugular veins</p> Signup and view all the answers

    How many anterior and posterior spinal arteries are present in the spinal cord?

    <p>1 anterior and 2 posterior</p> Signup and view all the answers

    What characteristic distinguishes the irregular pairs of the spinal veins?

    <p>They can be sometimes incomplete</p> Signup and view all the answers

    Which arteries are known to arise from spinal branches and run along spinal nerve roots?

    <p>Radicular medullary arteries</p> Signup and view all the answers

    What is the significance of the Circle of Willis in cerebral circulation?

    <p>It provides collateral blood flow in case of arterial blockage</p> Signup and view all the answers

    What form of neurological deficit is primarily associated with lacunar infarcts?

    <p>Contralateral hemiparesis of face, arm, and leg</p> Signup and view all the answers

    Which of the following accurately describes the drainage pattern of spinal veins?

    <p>They form a total of six veins draining into anterior and posterior channels</p> Signup and view all the answers

    How does the presence of the internal jugular veins relate to cerebral venous drainage?

    <p>They are the main drainage pathways for all cerebral veins</p> Signup and view all the answers

    What determines the flow of blood in the venous sinuses of the brain?

    <p>Gravity and intracranial pressure changes</p> Signup and view all the answers

    What role do thickened brain capillaries play in the prevention of brain edema?

    <p>They reduce the permeability of capillaries.</p> Signup and view all the answers

    What is the primary source of energy for the brain under normal resting conditions?

    <p>Glucose</p> Signup and view all the answers

    Which of the following can cause increased capillary pressure leading to brain edema?

    <p>Concussion</p> Signup and view all the answers

    What is the consequence of interrupted cerebral blood flow lasting longer than 5-8 minutes?

    <p>Irreversible neuron damage</p> Signup and view all the answers

    How does mannitol function as a treatment for brain edema?

    <p>As an intravascular hyperosmotic agent.</p> Signup and view all the answers

    What is the average rate of glucose consumption by brain tissue per day?

    <p>110g</p> Signup and view all the answers

    Which factor does NOT contribute to the regulation of cerebral blood flow?

    <p>Body temperature fluctuations</p> Signup and view all the answers

    What happens to the brain's oxygen storage capabilities during anaerobic metabolism?

    <p>They are nearly non-existent.</p> Signup and view all the answers

    What is the role of 'glial feet' in brain edema protection?

    <p>Regulating blood-brain barrier permeability.</p> Signup and view all the answers

    What is the arterial pressure range where autoregulation of cerebral blood flow remains constant?

    <p>60 to 140 mmHg</p> Signup and view all the answers

    Which statement is true regarding the brain's capacity for anaerobic metabolism?

    <p>It has low glycogen reserves and cannot sustain much anaerobic metabolism.</p> Signup and view all the answers

    Which of the following factors does NOT contribute to cerebral ischemia?

    <p>Normocapnic conditions</p> Signup and view all the answers

    What is a characteristic of the blood-brain barrier (BBB) at circumventricular organs?

    <p>It is missing or poorly formed.</p> Signup and view all the answers

    What type of substances have high permeability across the blood-brain barrier?

    <p>Gases like O2 and CO2</p> Signup and view all the answers

    What is a primary function of the blood-brain barrier?

    <p>To protect the brain from toxins</p> Signup and view all the answers

    Which imaging technology has replaced the use of radioactive isotopes for assessing vascular integrity in the brain?

    <p>CAT and NMR scans</p> Signup and view all the answers

    What occurs as a result of arterial pressure exceeding 180 mmHg?

    <p>Cerebral oedema or hemorrhage</p> Signup and view all the answers

    Which of the following substances is least likely to cross the blood-brain barrier?

    <p>Penicillin</p> Signup and view all the answers

    What role do astrocytes play in the blood-brain barrier?

    <p>They wrap around blood capillaries and support barrier integrity.</p> Signup and view all the answers

    What is the effect of cerebral ischemia on brain function?

    <p>Loss of consciousness</p> Signup and view all the answers

    What are the three protective systems that prevent brain edema?

    <p>Glial feet, thickening of brain capillaries, and constriction of arterioles.</p> Signup and view all the answers

    How does mannitol aid in treating brain edema?

    <p>Mannitol functions as an intravascular hyperosmotic substance, drawing water back into the capillaries.</p> Signup and view all the answers

    What is the primary source of energy for the brain during resting conditions?

    <p>Glucose stored as glycogen.</p> Signup and view all the answers

    What is the consequence of blood flow interruption to the brain lasting longer than 5-8 minutes?

    <p>Irreversible neuron damage occurs.</p> Signup and view all the answers

    Why is the brain's capability for anaerobic metabolism limited?

    <p>The brain has low glycogen storage and does not store significant oxygen.</p> Signup and view all the answers

    What regions of the brain are primarily affected by a blockage of the Middle Cerebral Artery (MCA)?

    <p>The lateral surface of the brain and the temporal pole are primarily affected.</p> Signup and view all the answers

    How does a blockage of the Anterior Cerebral Artery (ACA) manifest in a patient?

    <p>It typically results in paresis of the contralateral leg and sensory loss.</p> Signup and view all the answers

    What visual impairment is associated with a blockage of the Posterior Cerebral Artery (PCA)?

    <p>It often leads to contralateral homonymous hemianopia with macular sparing.</p> Signup and view all the answers

    Describe the neurological deficits resulting from an occlusion of the ACA.

    <p>The occlusion leads to mental impairment, gait issues, and urinary dysfunction.</p> Signup and view all the answers

    What is the significance of the Circle of Willis in relation to the cerebral arteries?

    <p>It provides an anastomosis that ensures collateral circulation to the brain.</p> Signup and view all the answers

    What are lacunar infarcts and where do they commonly occur?

    <p>Lacunar infarcts are small subcortical lesions that typically occur in the Internal Capsule.</p> Signup and view all the answers

    What is the role of the venous sinuses in cerebral venous drainage?

    <p>Venous sinuses are channels between the dura mater layers that allow for the drainage of cerebral veins.</p> Signup and view all the answers

    What distinguishes the arterial supply to the spinal cord?

    <p>The spinal cord receives blood supply primarily from one anterior spinal artery and two posterior spinal arteries.</p> Signup and view all the answers

    Describe the configuration of spinal veins involved in drainage.

    <p>The spinal veins consist of one anterior and one posterior vein, along with multiple paired anterolateral and posterolateral veins.</p> Signup and view all the answers

    How does hypertension contribute to neurological deficits?

    <p>Hypertension can lead to occlusion of penetrating arteries, causing lacunar infarcts and resulting in hemiparesis.</p> Signup and view all the answers

    What is the significance of the Circle of Willis in the context of lacunar infarcts?

    <p>The Circle of Willis serves as a crucial arterial network that can influence the potential for collateral circulation during lacunar infarcts.</p> Signup and view all the answers

    What is the overall function of radicular medullary arteries?

    <p>Radicular medullary arteries provide blood supply along the spinal nerve roots.</p> Signup and view all the answers

    Identify the type of neurological symptoms associated with lacunar infarcts.

    <p>Lacunar infarcts are commonly associated with hemiparesis of the contralateral face, arm, and leg.</p> Signup and view all the answers

    What two pairs of vessels primarily supply blood to the brain?

    <p>The internal carotid arteries and the vertebral arteries.</p> Signup and view all the answers

    Describe the pathway of the vertebral artery as it supplies the brain.

    <p>The vertebral artery ascends through the transverse foramina of the cervical vertebrae and enters the cranial cavity at the foramen magnum, where it unites to form the basilar artery.</p> Signup and view all the answers

    What branches does the internal carotid artery give rise to after entering the cranial cavity?

    <p>The internal carotid artery branches into the anterior and middle cerebral arteries.</p> Signup and view all the answers

    How does the blood supply differ between anterior and posterior circulation of the brain?

    <p>Anterior circulation is supplied by the internal carotid arteries, while posterior circulation is supplied by the vertebral arteries.</p> Signup and view all the answers

    What role does the basilar artery play in cerebral circulation?

    <p>The basilar artery supplies blood to the brainstem and cerebellum and branches into the posterior cerebral arteries.</p> Signup and view all the answers

    What anatomical structure do the internal carotid arteries pass through to reach the skull?

    <p>They enter the carotid canal located in the petrous part of the temporal bone.</p> Signup and view all the answers

    Why is the connection between the vertebral arteries significant?

    <p>The connection forms the basilar artery, which is critical for posterior cerebral circulation and brainstem perfusion.</p> Signup and view all the answers

    How does the anterior and posterior circulation of the brain ensure adequate blood supply?

    <p>They form an interconnected network through the Circle of Willis, allowing collateral circulation if one artery is compromised.</p> Signup and view all the answers

    Explain how increased intracranial pressure can lead to herniation of cranial content.

    <p>Increased intracranial pressure compresses brain structures and can force them to shift into regions where they do not normally fit, such as through the foramen magnum, leading to herniation.</p> Signup and view all the answers

    Identify the primary components that must maintain equilibrium according to the Monro-Kellie Doctrine.

    <p>The primary components are brain tissue, blood, and cerebrospinal fluid (CSF).</p> Signup and view all the answers

    What physiological changes occur in cerebral blood flow during hypercapnia?

    <p>Hypercapnia results in increased levels of CO2, leading to vasodilation and an increase in cerebral blood flow.</p> Signup and view all the answers

    Discuss the relationship between oxygen levels and cerebral blood flow during hypoxia.

    <p>During hypoxia, cerebral blood flow increases due to vasodilation in response to reduced oxygen levels.</p> Signup and view all the answers

    How does autoregulation of cerebral blood flow respond to fluctuations in arterial pressure?

    <p>Autoregulation maintains relatively constant cerebral blood flow despite changes in arterial pressure through vasodilation or vasoconstriction of cerebral vessels.</p> Signup and view all the answers

    What are the warning symptoms associated with elevated intracranial pressure?

    <p>Warning symptoms include neck stiffness, severe headaches, and papilledema.</p> Signup and view all the answers

    Describe the role of local vasodilator metabolites in regulating cerebral blood flow.

    <p>Local vasodilator metabolites like H+, K+, CO2, and adenosine increase cerebral blood flow by inducing vasodilation in active brain regions.</p> Signup and view all the answers

    Contrast the effects of hypocapnia and hypercapnia on cerebral blood flow.

    <p>Hypocapnia causes vasoconstriction and a decrease in cerebral blood flow, while hypercapnia causes vasodilation and an increase.</p> Signup and view all the answers

    Which cerebral artery supplies the medial and superior surfaces along with the frontal pole?

    <p>Anterior cerebral artery</p> Signup and view all the answers

    A blockage in the Middle Cerebral Artery (MCA) can lead to contralateral paralysis of the arm and the lower part of the face.

    <p>True</p> Signup and view all the answers

    What visual defect is typically associated with a blockage of the Posterior Cerebral Artery (PCA)?

    <p>Contralateral homonymous hemianopia</p> Signup and view all the answers

    The three cerebral arteries supply a _____ and a pole.

    <p>surface</p> Signup and view all the answers

    Match the following cerebral arteries with the corresponding areas they supply:

    <p>Anterior cerebral artery = Medial and superior surface, frontal pole Middle cerebral artery = Lateral surface, temporal pole Posterior cerebral artery = Inferior surface, occipital pole</p> Signup and view all the answers

    What is the main cause of lacunar infarcts?

    <p>Occlusion of penetrating arteries from a large cerebral artery</p> Signup and view all the answers

    The internal jugular veins drain blood directly from the spinal cord.

    <p>False</p> Signup and view all the answers

    What type of arteries descend inferiorly as branches of the vertebral artery to supply blood to the spinal cord?

    <p>Anterior and posterior spinal arteries</p> Signup and view all the answers

    The __________ are channels formed between the two layers of the dura mater that facilitate venous drainage in the brain.

    <p>venous sinuses</p> Signup and view all the answers

    Which venous structures are responsible for draining blood from the spinal cord?

    <p>Anterior and posterior spinal veins</p> Signup and view all the answers

    Match the spinal vein type with its description:

    <p>Anterolateral veins = Paired, irregular, and found laterally Posterolateral veins = Paired, irregular, and found laterally Anterior spinal veins = Single vein in midline Posterior spinal veins = Single vein in midline</p> Signup and view all the answers

    The radial medullary arteries arise from spinal branches of lumbar or intercostal arteries.

    <p>True</p> Signup and view all the answers

    What are the two main types of spinal arteries that supply blood to the spinal cord?

    <p>Anterior spinal artery and posterior spinal arteries</p> Signup and view all the answers

    What substance is used as a treatment for brain edema due to its hyperosmotic properties?

    <p>Mannitol</p> Signup and view all the answers

    The brain is capable of significant anaerobic metabolism due to stored oxygen.

    <p>False</p> Signup and view all the answers

    What is the primary energy source for the brain under normal resting conditions?

    <p>Glucose</p> Signup and view all the answers

    The brain is at risk of irreversible neuron damage if blood flow is interrupted for more than ___ minutes.

    <p>5-8</p> Signup and view all the answers

    Match the causes of brain edema with their descriptions:

    <p>Increased capillary pressure = Pushes fluid from capillaries into the brain Damage to capillary walls = Allows excess fluid leakage into brain tissue Mannitol treatment = Restores osmotic balance in capillaries</p> Signup and view all the answers

    What is the main consequence of increased intracranial pressure (ICP)?

    <p>Herniation of cranial contents</p> Signup and view all the answers

    Cerebral blood flow increases with elevated levels of oxygen (O2).

    <p>False</p> Signup and view all the answers

    What is the Monro-Kellie Doctrine?

    <p>It is the principle stating that the cranial cavity is a closed box and that changes in volume must be compensated by displacing other contents.</p> Signup and view all the answers

    An increase in _______ levels can lead to vasodilation and increased cerebral blood flow.

    <p>CO2</p> Signup and view all the answers

    Match the following conditions with their respective effects:

    <p>Hypoxia = Vasodilation Hypercapnia = Vasodilation Hypocapnia = Vasoconstriction Increased ICP = Optic nerve swelling</p> Signup and view all the answers

    Which metabolites are primarily involved in the regulation of cerebral blood flow?

    <p>H+, K+, CO2, O2, and adenosine</p> Signup and view all the answers

    A decrease in oxygen levels (hypoxia) leads to vasoconstriction in the brain.

    <p>False</p> Signup and view all the answers

    What is a common warning symptom of increased intracranial pressure (ICP)?

    <p>Severe headache</p> Signup and view all the answers

    What occurs at arterial pressures greater than 180 mmHg?

    <p>Cerebral edema or hemorrhage</p> Signup and view all the answers

    The blood-brain barrier is fully permeable to antibiotics such as penicillin.

    <p>False</p> Signup and view all the answers

    What is the primary function of the blood-brain barrier (BBB)?

    <p>To protect the brain from toxins and prevent neurotransmitter escape.</p> Signup and view all the answers

    Cerebral ischemia occurs when arterial pressure falls below _______ mmHg.

    <p>50</p> Signup and view all the answers

    Match the barriers with their corresponding characteristics:

    <p>BBB = Brain capillaries barrier Arachnoid barrier = External protective layer of the CNS Choroid epithelium = Produces cerebrospinal fluid Circumventricular organs = Areas where BBB is missing</p> Signup and view all the answers

    What is the level of permeability of the blood-brain barrier for gases like O2 and CO2?

    <p>High permeability</p> Signup and view all the answers

    Astrocytes play a role in forming tight junctions in brain capillaries.

    <p>True</p> Signup and view all the answers

    Which imaging technologies have replaced the use of radioactive isotopes for assessing vascular integrity in the brain?

    <p>CAT and NMR scans.</p> Signup and view all the answers

    Study Notes

    Radicular Veins

    • Drain into the internal vertebral venous plexus located between the dura mater and vertebrae.
    • Connect with the ascending lumbar, azygos, and hemiazygos veins for the lower spinal cord, while the upper spinal cord is connected via vertebral veins.
    • Ultimately return blood to the vena cava.

    Cerebral Blood Flow

    • Governed by the Monro-Kellie Doctrine, which states that the cranial cavity is a closed box that maintains a balance of brain tissue, blood, and cerebrospinal fluid (CSF).
    • Intracranial pressure (ICP) increases if there's a change in volume of intracranial contents, risking herniation and potential death.
    • Increased ICP indicators include neck stiffness, severe headaches, and papilledema.

    Increased Intracranial Pressure (ICP)

    • Papilledema, or swelling of the optic disc, is a direct sign of increased ICP examined via ophthalmoscope.
    • Normal ICP range is 10-20 cm H2O.

    Control of Blood Circulation (Brain)

    • The brain regulates its own blood flow despite constituting only 2.5% of body weight, receiving 15% of resting cardiac output (750-900 ml/min).
    • Normal cerebral blood flow is 50-65 ml/100 g/min, with constant total blood flow and oxygen consumption.
    • Local vasodilator metabolites such as H+, K+, CO2, and adenosine facilitate increased regional blood flow.

    Effect of O2 and CO2 on Cerebral Blood Flow

    • Increased CO2 or H+ ions lead to vasodilation, enhancing cerebral blood flow, while hyperventilation (decreased CO2) results in vasoconstriction and potential syncope.
    • Decreased O2 levels trigger vasodilation to maintain blood flow, although responses to O2 alterations are smaller compared to CO2.

    Brain Edema

    • Defined as fluid transudation from capillaries into brain tissue.
    • Protection against edema includes glial feet, thickened capillary walls, and constricted arterioles.
    • Causes include increased capillary pressure and capillary wall damage (e.g., concussion).
    • Mannitol, an intravascular hyperosmotic agent, is commonly used for treatment as it encourages fluid reabsorption into capillaries.

    Brain Metabolism

    • The brain accounts for 15% of the body's total metabolism while comprising only 2% of body mass.
    • Primary energy sources include glucose, ketones, lactate, and pyruvate.
    • The brain lacks substantial anaerobic metabolism capacity due to limited oxygen storage and low glycogen levels.
    • Approximately 110 g of glucose is consumed daily, and irreversible neuron damage can occur if blood flow is halted for longer than 5-8 minutes.

    Neurological Deficits in Cardiovascular Disease

    • Lacunar infarcts from occlusion/blockage of penetrating arteries commonly impact the Internal Capsule, resulting in hemiparesis of the contralateral face, arm, and leg.

    Brain Venous Drainage

    • Comprised of venous sinuses, formed between the two dura mater layers, into which cerebral veins drain before the internal jugular veins.

    Spinal Cord: Arterial Blood Supply

    • Supplied by one anterior spinal artery and two posterior spinal arteries that branch from the vertebral artery.
    • Radicular medullary arteries accompany spinal nerve roots and originate from lumbar or intercostal arteries.

    Spinal Cord: Venous Drainage

    • Consists of anterior and posterior spinal veins, with additional irregularly paired anterolateral and posterolateral spinal veins.

    Autoregulation of Cerebral Blood Flow

    • Maintained between arterial pressures of 60 to 140 mmHg, with optimal autoregulation under normal CO2 levels.
    • Pressures below 50 mmHg risk ischemia; pressures above 180 mmHg can cause edema or hemorrhage.

    Blood-Brain Barrier (BBB)

    • Constructed from brain capillaries, arachnoid barrier, and choroid epithelium.
    • BBB absent at circumventricular organs to allow hormonal communication, while astrocyte extensions surround capillaries.
    • Permeable to gases (O2, CO2), but impermeable to larger substances like antibiotics and proteins, complicating infection treatments.

    Functions of the Blood-Brain Barrier (BBB)

    • Protects the brain from various toxins.
    • Prevents neurotransmitter escape from the CNS.

    Blood Supply to the Brain

    • The brain receives blood supply from two main artery pairs: internal carotid arteries (anterior circulation) and vertebral arteries (posterior circulation).
    • Internal carotid arteries ascend to the skull base and give off the ophthalmic artery, branching into the anterior and middle cerebral arteries that enter the subarachnoid space.
    • Vertebral arteries originate from the subclavian artery, ascend through cervical vertebrae, and form the basilar artery upon uniting at the medulla.

    Circle of Willis

    • The Circle of Willis represents anastomosis of arteries supplying the cerebrum, surrounding the optic chiasma and infundibulum of the pituitary gland.
    • Supplies the brainstem and offers collateral circulation between cerebral arteries.

    Cerebral Arteries and Their Areas of Supply

    • Anterior cerebral artery: Supplies the medial and superior surfaces of the frontal lobe.
    • Middle cerebral artery: Supplies the lateral surface and temporal pole.
    • Posterior cerebral artery: Supplies the inferior surface and occipital pole.

    Neurological Deficits from Cerebral Artery Blockage

    • Anterior cerebral artery blockage leads to leg paresis, sensory loss, and cognitive impairments.
    • Middle cerebral artery blockage causes contralateral arm paralysis, facial weakness, and potential language loss if dominant hemisphere affected.
    • Posterior cerebral artery blockage results in visual field defects, amnesia, and visual perceptual disorders.

    Venous Drainage of the Brain

    • Venous sinuses are formed between layers of the dura mater and cerebral veins drain into these sinuses, ultimately into the internal jugular veins.
    • Superficial and deep veins have complex arrangements draining various areas of the brain.

    Blood Supply to the Spinal Cord

    • Supplied by one anterior and two posterior spinal arteries, which are branches of the vertebral artery.
    • Features radicular medullary arteries arising from lumbar or intercostal arteries along spinal nerve roots.

    Venous Drainage of the Spinal Cord

    • Comprised of anterior and posterior spinal veins, alongside additional anterolateral and posterolateral veins.
    • Drains into the internal vertebral venous plexus and subsequently into the vena cava.

    Cerebral Blood Flow

    • Governed by the Monro-Kellie Doctrine, indicating cranial contents must remain in balance to maintain normal intracranial pressure (ICP).
    • The brain accounts for 15% of resting cardiac output, with normal flow rates between 50 to 65 ml per 100 g of brain tissue per minute.

    Influence of Oxygen and Carbon Dioxide on Cerebral Blood Flow

    • Increased CO2 or H+ levels cause vasodilation, enhancing cerebral blood flow; conversely, hyperventilation leads to vasoconstriction.
    • Decreased O2 levels also promote vasodilation, but the response to CO2 changes is more pronounced.

    Brain Edema

    • Defined as fluid transudation from capillaries, with protective mechanisms including glial cells and thickened capillary walls preventing damage from high blood pressure.
    • Causes include elevated capillary pressure and damage from concussions; treated with mannitol to draw fluid back into circulation.

    Brain Metabolism

    • The brain encompasses 15% of total body metabolism despite being only 2% of total body mass.
    • Primary energy sources include glucose (from glycogen), ketones, lactate, and pyruvate.
    • Minimal anaerobic metabolism capability; reliant on a constant cerebral blood flow with irreversible damage occurring if blood flow halts for over 5-8 minutes.
    • Daily glucose consumption by the brain is approximately 110 g.

    Cerebral Arteries: Circle of Willis

    • The Circle of Willis is an anastomosis of arteries supplying the cerebrum.
    • It encircles the optic chiasma and infundibulum of the pituitary gland.

    Cerebral Artery Supply

    • Anterior Cerebral Artery (ACA): Supplies the medial and superior surfaces of the frontal pole.
    • Middle Cerebral Artery (MCA): Supplies the lateral surface and temporal pole.
    • Posterior Cerebral Artery (PCA): Supplies the inferior surface and occipital pole.

    Neurological Deficits: Blockages

    • ACA blockage results in:

      • Paresis of the contralateral leg and sensory loss.
      • Impaired gait and micturition.
      • Mental impairment and dyspraxia.

    • MCA blockage leads to:

      • Contralateral paralysis of the arm and lower face (upper motor neuron lesion).
      • Contralateral sensory loss and potential loss of language if the dominant hemisphere is affected.

    • PCA blockage causes:

      • Visual field defects (usually contralateral homonymous hemianopia with macular sparing).
      • Amnesic syndrome and language disorders.
      • Complex visual perceptual abnormalities.

    Contralateral Homonymous Hemianopia

    • Refers to the visual fields of both eyes (temporal and nasal) corresponding to areas in the visual pathways (temporal and nasal hemiretinas).

    Neurological Deficits and Cardiovascular Disease

    • Occlusion of penetrating arteries from major cerebral arteries can lead to lacunar infarcts.
    • Symptoms include hemiparesis of the contralateral face, arm, and leg, crossing specific cerebral artery domains.

    Venous Drainage of the Brain

    • Venous sinuses are channels between the dura mater layers.
    • Cerebral veins drain into these sinuses, ultimately emptying into the internal jugular veins.

    Spinal Cord Blood Supply

    • Supplied by one anterior and two posterior spinal arteries from the vertebral artery.
    • Radicular medullary arteries arise from lumbar or intercostal arteries.

    Spinal Cord Venous Drainage

    • One anterior and one posterior spinal vein are midline; two anterolateral and two posterolateral veins are irregular and paired.
    • These drain through anterior and posterior radicular veins to the internal vertebral venous plexus.

    Cerebral Blood Flow

    • Governed by the Monro-Kellie Doctrine, which states that the cranial cavity is a closed box where changes in blood volume affect intracranial pressure (ICP).
    • Increased ICP can lead to herniation and severe neurological impairment.

    Intracranial Pressure (ICP)

    • Symptoms of increased ICP include neck stiffness, severe headaches, and papilledema.
    • Papilledema indicates increased pressure affecting the optic nerve.

    Control of Cerebral Blood Circulation

    • The brain maintains autonomy over its blood flow, constituting 2.5% of body weight and receiving 15% of resting cardiac output.
    • Total cerebral blood flow remains consistent despite varying demands due to local metabolite release.

    Effects of Oxygen and Carbon Dioxide on Cerebral Blood Flow

    • High levels of CO2 and H+ ions cause vasodilation, increasing cerebral blood flow.
    • Hypoxia also leads to increased blood flow, while low CO2 results in vasoconstriction, which can lead to syncope.

    Autoregulation of Cerebral Blood Flow

    • Effective within a range of arterial pressures (60 to 140 mmHg).
    • Pressures below 50 mmHg cause cerebral ischemia, while pressures above 180 mmHg can lead to cerebral edema or hemorrhage.

    Blood-Brain Barrier (BBB)

    • Comprises three barriers: endothelial brain capillaries, the arachnoid barrier, and the choroid epithelium.
    • The BBB is absent in circumventricular organs, allowing limited diffusion for certain substances.

    BBB Permeability

    • High permeability for gases (O2, CO2) and lipid-soluble substances.
    • Low permeability for proteins and antibiotics, complicating treatment for brain infections.

    Functions of the Blood-Brain Barrier

    • Protects the brain from toxins and prevents neurotransmitter leakage into circulation.
    • Maintains a stable microenvironment for neurons.

    Brain Edema

    • Defined as fluid transudation from capillaries into brain tissue.
    • Protective mechanisms include glial feet and the structural integrity of capillaries.
    • Causes include increased capillary pressure and damage from trauma (e.g., concussion).

    Brain Metabolism

    • The brain consumes 15% of total body metabolism despite being only 2% of body mass.
    • Primarily relies on glucose, but can utilize ketones and lactate during metabolic stress.

    Brain Energy Supply

    • Limited capacity for anaerobic metabolism with only a small, short-term glycogen reserve.
    • Continuous supply of glucose is critical, with irreversible damage occurring after 5-8 minutes of ischemia.

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    Blood Supply and Brain Metabolism PDF

    Description

    This quiz explores key concepts related to cerebral blood flow, the Monro-Kellie Doctrine, and the implications of increased intracranial pressure (ICP). It examines the anatomy and physiological mechanisms involved in regulating blood circulation in the brain, as well as signs indicative of altered ICP. Test your knowledge on the important connections and functions relevant to cerebral health.

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