Central Blood Flow Regulation and the Blood-Brain Barrier

Question 1

How much oxygen is supplied to the brain per minute?

Answer 1

55 ml/100g of tissue/min

Question 2

Why is there a vast surplus of glucose delivery to the brain?

Answer 2

Because the brain can only metabolise glucose

Ketone bodies can be metabolized if there is a shortage of glucose but glucose is the main nutrient

Question 3

Blood glucose below what value will lead to loss of consciousness, coma and death?

Answer 3

2 mM

Question 4

On what levels do you get regulation of cerebral blood flow?

Answer 4

Mechanisms affecting total cerebral blood flow

Mechanisms that relate activity to requirement in specific brain regions by altered localised blood flow

Question 5

Between what range in mean arterial blood pressure can autoregulation maintain a constant cerebral blood flow?

Answer 5

60-160 mm Hg

Question 6

Name one important factor to do with the smooth muscle lining arterioles that allows regulation of blood flow.

Answer 6

Myogenic Mechanism – when the smooth muscle surrounding arterioles is stretched, it will contract to maintain a constant blood flow
This occurs when there is a change in blood pressure in the body

Question 7

What are the two types of control of cerebral blood flow regulation?

Answer 7

Neural and Chemical

Question 8

What are the four types of neural control of cerebral blood flow?

Answer 8

Sympathetic innervation of the main cerebral arteries – causes vasoconstriction when arterial blood pressure is high
Parasympathetic (facial nerve) stimulation – can cause a little bit of vasodilation
Central cortical neurons – neurons within the brain itself can release neurotransmitters such as catecholamines that cause vasoconstriction
Dopaminergic neurons – produce vasoconstriction (important in regulating differential blood flow to areas of the brain that are more active)

Question 9

What feature do capillaries in the brain have that allow them tocontract?

Answer 9

They are surrounded by pericytes, which are contractile cells
They are a type of brain macrophage that have several functions e.g. contractile, immune function, transport properties

Question 10

What do the dopaminergic neurons affecting cerebral blood flow innervate?

Answer 10

Pericytes around capillaries and smooth muscle around arterioles

Question 11

Dopaminergic neurons cause contraction of pericytes via which receptors?

Answer 11

Aminergic and serotoninergic neurons

Question 12

Which fibres innervate the main arteries in the brain?

Answer 12

Sympathetic fibres

Question 13

Name some chemical factors that increase blood flow to particular tissues.

Answer 13

Carbon dioxide  
NO
pH
Anoxia 
Adenosine 
K+
Other (e.g. kinins, prostaglandins, histamine, endothelins)

Question 14

How does change in pH affect blood flow?

Answer 14

The lower the pH (the higher the H+ concentration) the more the vesselvasodilates

Question 15

Describe how carbon dioxide indirectly causes vasodilation in the cerebral vessels.

Answer 15

H+ ions can’t cross the blood-brain barrier but carbon dioxide can
Carbon dioxide moves from the blood through the blood-brain barrier into the smooth muscle cells
Within the smooth muscle cells, in the presence of carbonic anhydrase, the carbon dioxide reacts with water to form bicarbonate and H+ ions
This internally generated H+ ions within the smooth muscle cells cause smooth muscle relaxation (vasodilation)

Question 16

Describe how nitric oxide (NO) causes vasodilation.

Answer 16

Nitric oxide stimulates guanylyl cyclase
Guanylyl cyclase converts GTP - cGMP
cGMP causes vasodilation

Question 17

Where is CSF produced?

Answer 17

Choroid plexus – these are specific cells associated with the ventricles (in particular the lateral ventricles)

Question 18

What name is given to parts of the brain that receive blood flowlike anywhere else but do not have a blood-brain barrier?

Answer 18

Circumventricular organs

Question 19

Describe the passage of CSF through the ventricular system.

Answer 19

CSF is produced by specialized ependymal cells of the choroid plexus (mainly in the lateral ventricles)
From the lateral ventricles it goes through the foramen of Monro to the 3rd ventricle
From the 3rd ventricles, CSF flows down the cerebral aqueduct to the 4th ventricle
From the 4th ventricle it enters the subarachnoid space (via medial and lateral apertures) and eventually drains back into the venous system via arachnoid granulation

Question 20

What is the volume of CSF in a normal person?

Answer 20

80-150 mL

Question 21

What is the volume of CSF formed per day?

Answer 21

450 mL/day

Question 22

State three functions of the CSF.

Answer 22

Protection (chemical and physical)
Nutrient provision to neurons
Transport of molecules

Question 23

Describe the structure of the blood-brain barrier. Which cells areinvolved?

Answer 23

The capillaries in the brain have endothelial cells with very tight junctions so there is tight control of what can pass through the wall of the capillary
The capillaries are also surrounded by pericytes with end-feet runningalong the capillary wall
When the pericytes contract they make it more likely for the molecules to leave the capillary

Question 24

What type of molecule can cross the blood-brain barrier easily?

Answer 24

Lipophilic molecules

Question 25

How do water and glucose cross the blood-brain barrier?

Answer 25

Water pass through aquaporin molecules

Glucose passes through Glut 1 transporters

Question 26

Name three circumventricular organs.

Answer 26

Median eminence region of the hypothalamus
Subfornical organ
Organum vasculosum of the lamina terminalis

Question 27

State four components that have a lower concentration in the CSF than the plasma.

Answer 27

K+
Calcium
Amino acids
Bicarbonate

Question 28

State two components that have a higher concentration in the CSF than the plasma.

Answer 28

Magnesium

Chloride

Question 29

How is the osmolarity different between the CSF and the plasma?

Answer 29

The same

Question 30

How is the pH different in the CSF compared to the plasma?

Answer 30

CSF is slightly more acidic