CBF Regulation And BBB

Question 1

What happens to the brain after CBF is interrupted

Answer 1

When blood flow to the brain is interrupted = insufficient oxygen delivery, unconsciousness and after a few minutes irreversible damage.

Syncope (fainting) is a common manifestation of reduced blood supply to the brain, causes are reduced blood pressure, postural changes, vasovagal attack, sudden pain, emotional shock.

Question 2

Describe the importance of glucose supply to the Brain.

Answer 2

Normally it’s a vast supply because the brain can’t synthesise or utilise anything else, so severe hypoglycaemia can lead to brain function loss, if less than 2 mm - unconsciousness, coma, death (normal fasting should be 4-6mm)

Question 3

What are the mechanisms that regulate cerebral blood flow?

Answer 3

1. Mechanisms affecting total CBF

2. Mechanisms which relateactivity to the requirement in specific brain regions by altered loacalised blood flow.

Question 4

Explain the mechanisms affecting total CBF

Answer 4

Autoregulated at 60-160, over a wide range of arterial pressures, the arteries/ arterioles dilate or contract to maintain blood flow.

Myogenic = stretch sensitive cerebral vascular smoothe muscle dilate at high BP and contract at low BP

However above this range, any increased blood flow can lead to swelling of brain tissue which is not accommodated by the closed cranium

Question 5

What are two local mechanisms of control of CBF

Answer 5

1. Natural control: (a) SNS - sympathetic innervation of the main cerebral arteries can cause vasoconstriction when arterial blood pressure is high. (B) PNS (facial) cause slight vasodilation (C) central corticol neurones = neurones within the brain itself that can release neurotransmitter such as catecholamines that cause vasoconstriction (D) dopaminergic neurones produce vasoconstriction effect related to brain activity.
2. Chemical factors: Co2 - vasodilator, PH - vasodilator, NO - vasodilator,
   K+ - vasodilator, adenosine - vasodilator, anoxia - vasodilator.

Question 6

Describe the control of cerebral arterial vasodilation via Co2

Answer 6

Co2 from the blood or local metabolism generates H+ using carbonic anhydride in surrounding neural tissue and in smoothe muscle cells. Elevated H+ means lower PH which causes relaxation of muscle and dilation of vessels = increased blood flow.

Question 7

Explain the fluid compartments of the brain.

Answer 7

CSF produced be regions of choroid plexus in the cerebral ventricles which is a protective mechanism. The ventricles, aqueduct and canals of the brain are lined with ependymal cells which form the choroid plexus.

Question 8

Describe the Formation of the CSF by choroid plexus

Answer 8

1. Capillaries are leaky but local ependymal cells have extensive tight junctions
2. Secrete CSF into ventricles (lateral, 3rd ventricles via the intraventricular foramina, down central aqueduct into 4th ventricle and into subarachnoid space via medical and lateral apparatus - circulates).

Question 9

What are the 3 functions of the CSF

Answer 9

1. Protection (chemical and physical)
2. Nutrition of the neurones
3. Transport of molecules

Question 10

Describe the function of BBB

Answer 10

1. Protected the brain tissue from certain toxins and circulating transmitters like catecholamines
2. Protected the brain from weird variations of ion concentrations

Question 11

Describe the structure of BBB

Answer 11

BBB capillaries gave extensive tight junctions at the endothelial cell-cell contacts, massively