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Flashcards in Physiology-Cerebral Circulation Deck (11)
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1

What arteries originate outside of the brain and contribute to the circle of Willis?

Internal carotids and vertebral arteries

2

What portion of the brain would be affected if there was a thromboembolism in the middle cerebral artery? 

The middle cerebral artery supplies much of the outer motor cortex of the brain and is actually the most common site of thromboembolism in stroke. This is why you see motor deficiencies so often in ischemic stroke.

3

What are the different cells that surround the capillary endothelial cells in the brain and create the blood-brain barrier?

Microglia, pericytes, neurite and astrocytes.

4

Since the brain also has arterioles, it has smooth muscle cells that release substances into the blood: adenosine, H+, K+, CO2, O2 and lipids. Which of these substances can cross the blood-brain barrier?

CO2, O2 and lipids can cross. Adenosine, H+ and K+ cannot. Adenosine, K+ and H+ are released from INSIDE the brain to modulate blood flow.

5

A patient comes to see you after having a stroke. MRI studies reveal and expanding mass within the spinal cord, increasing CSF pressure. If arterial pressure is 100mmHg, what might his CSF pressure have been to cause his stroke?

50mmHg. Perfusion pressure is equal to arterial - venous pressures. However, when CSF pressure exceeds venous pressure, perfusion pressure to the brain = arterial pressure - CSF pressure. A CSF pressure of 50mmHg leaves him with 50mmHg perfusion pressure, which is the point at which you see ischemic reactions in the brain.

6

A 23 year old male comes to the ER after a car crash with cerebral hemorrhage. Before operating, the neurosurgeon has the anesthesiologist hyperventilate the patient. Why would he do this?

The brain is sensitive to CO2. As [CO2] decreases, blood vessels constricts and bleeding decreases.

7

A newborn baby is having difficulty getting rid of CO2 and it is accumulating rapidly. At what partial pressure of CO2 do you need to start monitoring and controlling the blood pressure of the baby?

60mmHg. It is at this point the brain no longer auto regulates and blood flow to the brain will become linear. At this point blood pressure will need to be regulated by the doctor.

8

What causes the brain to stop auto regulation of blood flow at this point?

It is the point at which hemoglobin saturation comes off of the plateau phase.

9

What substances play a role in modulating and auto regulating blood flow in the brain?

NO, prostaglandins (secreted by astrocytes), K+, H+ and adenosine.

10

What type of role does neural control play in auto regulation of blood flow to the brain?

The circle of Willis and arteries in the pia matter re well innervated by the adrenergic, cholinergic and NANC nerves. However, local control by far trumps neural control.

11

Why are gliomas and neuromas so difficult to treat with chemotherapy?

Chemotherapy involves the use of highly charged particles that cannot cross the blood-brain barrier.

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