16: Cerebral Vasculature Flashcards
How much blood is required per minute?
750ml
What makes up the circle of Willis?
2 internal carotids + basilar A (from 2 vertebral A’s)
Explain the Circle of Willis
There is little mixing of blood in is - so blockage of blood flow will only impact part of the brain, causing localized ischemia
Two neurotransmitters for symp innervation of cerebral circulation
Norep, neuropeptide Y
What does parasymp innervation do in cerebral circulation
Vasodilation of larger blood vessels, but physiological relevance is uncertain
Three neurotransmitters for parasymp innervation of cerebral circulation
Ach, VIP, PHM-27
What does VIP stand for
Vasoactive intestinal polypeptide
What is PHM-27 derived from?
Pre-pro-VIP
What happens with sensory innervation to cerebral circulation with decreased CSF volume
Brain is effectively heavier, and simple motion can cause torsion of blood vessels, causing pain
Why is autoregulation of cerebral circulation important?
high BP could damage the BBB
How does the body protect against high BP in the brain?
Symps in the brain will vasoconstric vasculature, increasing systemic BP but protecting the brain and BBB from damage
Four factors that can increase intracranial pressure
- Hydrocephaly
- Cerebral edema
- Intracranial bleeding
- Tumor
How much CSF is present in a given moment?
150ml
How much CSF is made in a day?
550ml
Weight of brain in air vs with CSF
In air: 1400g
In CSF: 50g
Four ventricles in the brain
Two lateral ventricles, third ventricle, fourth ventricle
Flow of CSF generally
Is in one direction through the ventricular system
What absorbs CSF at the end of its path?
Arachnoid villi
Primary mechanism of arachnoid villi CSF absorption (and a secondary method)
Bulk flow of CSF into venous sinus (also uses pinocytosis)
Absorption of CSF is proportional to what?
Intracranial pressure
Normal intracranial pressure (in mmCSF)
112 mmCSF
If intracranial pressure is below what value, CSF will not be reabsorbed?
Below 68mm CSF
How many times more dense is mmHg vs mm CSF?
X13
What area makes the most CSF and how much of it is it making? Where is the rest of CSF made?
Choroid plexus: makes 50-70% of CSF
Other locations: lining of ventricles
Surface area in choroid plexus
Is v high to make lots of CSF
Why is HCO3 important in CSF?
Controls pH
How do Mg and Cl enter CSF?
Are added in
How does CO2 enter CSF
Due to neuronal metabolism
Why must K be tightly controlled in CSF?
Is permeable to neuronal membrane
Why must Ca be tightly controlled in CSF?
Can be toxic
Does glucose cross BBB readily?
No it does not
Two components of the brain capillaries that limit exchange in the BBB
- Tight junctions between endothelial cells
2. Glial endfeet: come into close contact with blood vessels
Three major functions of the BBB
- Protect CSF from blood-borne agents and toxins
- Maintains electrolyte composition (mostly K)
- Maintains Vm
What do P-glycoprotein and MDR1 stand for?
Pump glycoprotein, multi-drug resistance protein 1
What is the neurohypophysis?
Posterior pituitary
Why are there four regions with a handicapped BBB?
They require exposure to blood substances
What are the capillaries like in circumventricular organs?
Capillaries doesn’t have tight junctions
Circumventricular organs
The four brain regions with a handicapped BBB
