Peripheral vascular physiology Flashcards
What is the rate of cerebral blood flow?
750ml per minute
What percentage of the cardiac output does the brain receive per minute?
15-20%
In what 3 ways is the cerebral circulation adapted for it’s specialised nature?
Arterial anastamoses
BBB
Autoregulatory mechanisms
Why is the circle of Willis important?
Because this anastomosis provides collateral blood supply which is protective against cerebral ischaemia
Which 3 paired vessels are the main constituents of the circle of willis?
Anterior referral arteries
Internal carotid arteries
Posterior cerebral arteries
Which vessels connect the 3 paired vessels together to complete the circle of willis?
Anterior and posterior communicating arteries
What is the blood brain barrier?
A high selective permeable barrier that separates blood from the brain ECF in the CNS
Which 2 properties of the brain endothelium allow the BBB to be effective?
Tight junctions that prevent paracellular movement of molecules
AND
No transendothelial pathways (i.e. intracellular vesicles)
What is the BB permeable to?
Water
Non-ionised lipid soluble substances (barbiturates, ethanol, caffeine)
What is the BBB impermeable to?
Proteins
Protein-bound substances (drugs, hormones)
Strongly hydrophilic substances (Na/ K)
Most bacteria, antibodies and antibiotics (too large to cross BBB)
What allows molecules with low lipid solubility to move across the BBB?
Carrier-mediated transport.
How does glucose cross the BBB and enter the brain?
Enters the brain via the GLUT-1 transport protein.
What are the main auto regulatory mechanisms that help to regulate cerebral blood flow?
Myogenic and metabolic autoregulation
What is myogenic auto regulation?
A mechanism that regulates local blood flow to the brain by allowing changes in the diameter of blood vessels in response to changes in BP.
What does a fall in blood pressure do to vessels in the brain?
Compensatory vasodilation of blood vessels = increased blood flow
At what blood pressure does myogenic auto regulation fail?
50mmHg (blood vessels cannot dilate any further at this point)
What is metabolic auto regulation?
A mechanism that helps to maintain local blood flow to the brain by allowing compensatory changes in blood vessel diameter in response to changes in the partial pressure of arterial CO2.
What does metabolic auto regulation respond to?
CO2
What does myogenic auto regulation respond to?
Blood pressure
What does hypercapnia cause to happen to vessels in the brain?
Vasodilation
**Hypercapnia is indicative of high metabolic demand = increased blood flow needed
What does hypocapnia cause to happen to vessels in the brain?
Vasoconstriction
An increase in which ion causes vasodilation in the cerebral circulation?
Potassium
How is the pulmonary circulation adapted to facilitate consistent gas exchange for high volumes of blood?
Anatomical adaptations
Short diffusion distance
Hypoxic pulmonary vasoconstriction
Give the 3 anatomical adaptations of pulmonary circulation that allow for effective gas exchange.
Low pressure system
Low resistance system
Large surface area for gas exchange