15 Questions
What is the primary reason why the brain has a high capillary density?
To meet the brain's high oxygen demand
What is the effect of an increase in blood flow on vessel diameter in the brain?
Vasoconstriction
What is the primary stimulus for metabolic autoregulation in the brain?
Change in pCO2 levels
What is the effect of Cushing's reflex on heart rate?
Decrease in heart rate
What is the primary function of skeletal muscle circulation during exercise?
To meet the metabolic need of the muscle
What is the effect of a pathological increase in intracranial pressure on blood flow to the brain stem?
Decrease in blood flow
What is the term for the triad of symptoms that occurs when Cushing's reflex fails?
Cushing's triad
What is the primary mechanism by which the Circle of Willis maintains a constant blood supply to the brain?
Anastomoses between basilar and internal carotid arteries
What is the primary reason why the brain is very intolerant to reduced blood supply?
Because it has a high oxygen demand
Which of the following adaptations helps maintain a constant blood supply to the brain in case one side fails?
Circle of Willis
What is the effect of hypocapnia on cerebral blood flow?
Vasoconstriction
What is the primary function of skeletal muscle circulation during rest?
Maintain a basal level of blood flow
Which of the following is NOT a feature of cerebral circulation?
Long diffusion distance
What is the effect of increased intracranial pressure on sympathetic activity?
Increased sympathetic activity
Which of the following is a feature of Cushing's reflex?
Increased sympathetic activity
Study Notes
Cerebral Circulation
- Brain has a high oxygen demand and is very intolerant to reduced blood supply.
- Interruptions in blood supply can lead to unconsciousness within 5 seconds and irreversible damage after 4 minutes.
- Adaptations to ensure constant blood flow include:
- High capillary density in the brain.
- Short diffusion distance of approximately 10 um.
- High basal flow rate.
- High oxygen extraction from the blood.
Maintenance of Constant Blood Flow
- Structural adaptations:
- Circle of Willis, which provides anastomoses between basilar and internal carotid arteries, ensuring a constant blood supply to the brain.
- Functional adaptations:
- Myogenic autoregulation:
- Increase in blood pressure leads to constriction of blood vessels.
- Decrease in blood pressure leads to vasodilation.
- Metabolic autoregulation:
- Increase in pCO2 (hypercapnia) leads to vasodilation.
- Decrease in pCO2 (hypocapnia) leads to vasoconstriction.
- Myogenic autoregulation:
Cushing's Reflex
- Pathological increase in intracranial pressure (ICP) compresses the brain, leading to:
- Impaired blood flow to the brain stem.
- Increase in sympathetic activity.
- Increase in blood pressure.
- Increase in blood flow.
- If this fails, Cushing's triad occurs, characterized by:
- Bradycardia.
- Irregular respiration.
- Systolic hypertension.
Skeletal Muscle Circulation
- Functions:
- Meeting metabolic needs during exercise.
- Many capillaries are closed off from the rest of the circulation due to the contraction of pre-capillary sphincters.
Cerebral Circulation
- Brain has a high oxygen demand and is very intolerant to reduced blood supply.
- Interruptions in blood supply can lead to unconsciousness within 5 seconds and irreversible damage after 4 minutes.
- Adaptations to ensure constant blood flow include:
- High capillary density in the brain.
- Short diffusion distance of approximately 10 um.
- High basal flow rate.
- High oxygen extraction from the blood.
Maintenance of Constant Blood Flow
- Structural adaptations:
- Circle of Willis, which provides anastomoses between basilar and internal carotid arteries, ensuring a constant blood supply to the brain.
- Functional adaptations:
- Myogenic autoregulation:
- Increase in blood pressure leads to constriction of blood vessels.
- Decrease in blood pressure leads to vasodilation.
- Metabolic autoregulation:
- Increase in pCO2 (hypercapnia) leads to vasodilation.
- Decrease in pCO2 (hypocapnia) leads to vasoconstriction.
- Myogenic autoregulation:
Cushing's Reflex
- Pathological increase in intracranial pressure (ICP) compresses the brain, leading to:
- Impaired blood flow to the brain stem.
- Increase in sympathetic activity.
- Increase in blood pressure.
- Increase in blood flow.
- If this fails, Cushing's triad occurs, characterized by:
- Bradycardia.
- Irregular respiration.
- Systolic hypertension.
Skeletal Muscle Circulation
- Functions:
- Meeting metabolic needs during exercise.
- Many capillaries are closed off from the rest of the circulation due to the contraction of pre-capillary sphincters.
This quiz covers the importance of cerebral circulation, brain's oxygen demand, and adaptations to maintain blood flow. It also explores how secure blood flow is maintained in the brain.
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