7 - Microcirculation Flashcards
What is blood flow rate? What is the equation?
Volume of blood passing through a vessel per unit time. Flow rate (Q) = Pressure gradient(P) / Resistance(R)
What is pressure gradient? Increase in pressure gradient affects what?
Pressure A (at start of arteriole, MAP) - Pressure B (end of arteriole)
Bigger pressure gradient = increased flow rate
What is resistance and what factors affect resistance in blood vessels?
Hinderance to blood flow due to friction between moving fluid and stationary vascular walls.
Vessel Length
Vessel Radius
Blood Viscosity
How does increased blood pressure affect flow rate and pressure gradient?
Pressure gradient increases = Flow rate increases
How does arteriolar vasoconstriction affect resistance and flow rate?
Resistance increases = Flow rate decreases
How do you determine blood flow to an organ? (equation)
F(organ) = Pressure gradient (MAP) / Resistance (organ)
Pressure gradient is MAP as capillary pressure is so small its negligible.
What is vasoconstriction?
Contraction -
Radius decreases
Resistance increases
Flow rate decreases
What is vasodilation?
Relaxation -
Radius increases
Resistance decreases
Flow rate increases
What is vascular tone and why is it important?
The partial constriction which is always present in arteriolar smooth muscle.
Important as it allows both constriction and dilation to occur.
What are the 2 reasons that the radius of arterioles is adjusted?
- To match blood flow to metabolic needs of tissue (intrinsic control)
- To maintain blood pressure (extrinsic control)
Function 1: What is chemically driven change in vasodilation of arterioles? What is this also called?
e.g. during exercise a cell requires more metabolites and more oxygen. This causes vasodilation so blood flow increases.
Called active hyperaemia
What does hyperaemia mean?
Increase in blood flow to an area.
Function 1: How can vasoconstriction be physically driven?
If blood temperature drops
If blood vessels are physically stretched (due to increased bp)
What is myogenic autoregulation?
Pressure induced vasocontriction.
e.g. When blood vessels are physically stretched (due to increased bp)
Also allows blood to go where it needs to go.
What is the equation for blood pressure (MAP)
Cardiac output x Total peripheral resistance
Function 2: How is blood pressure regulated?
Neural control - cardiovascular control centre in medulla controls vasoconstriction to control blood flow to specific organs.
Function 2: What are 3 major hormonal vasoconstrictors?
Vasopressin
Angiotensin II
Adrenaline/Noradrenaline
Arterioles are the major WHAT vessels?
Resistance
What is the purpose of the capillaries?
To deliver metabolic substrates to the cells of an organism.
Why is capillary density important?
To minimise diffusion distance
To maximise surface area for diffusion
What is a pre-capillary sphincter?
Wraps around beginning of capillary to effectively shut off a capillary network if it is not needed at that time.
Why do some structures have denser capillary networks? Examples.
Because they are more metabolically active - brain and skeletal muscle (DURING EXERCISE ONLY).
Lung capillary network is massive as it is the location for gas exchange.
What are the 3 types of capillary?
Continuous
Fenestrated
Discontinuous
What is in the continuous capillary gap junction?
Water
