Microcirculation Flashcards
Aim of cardiovascular system
Adequate blood flow through the capillaries
What is blood flow rate defined as
Volume of blood passing through a vessel per unit time
Flow rate
Flow rate=pressure gradient/resistance
State the law that is linked with the fluid circuit and state the equation of this law?
Darcy’s Law
Delta P = Q x R
Where q is flow rate
What would increasing the pressure gradient do?
Increases flow rate- we would increase pressure A by vasodilation and therefore increased blood flow rather than vasoconstriction (because although constriction would technically increase pressure, less blood would flow through it so less pressure)
Pressure difference importance
Without it blood wouldn’t reach tissue capillary bed
Define resistance in terms of blood flow
Hindrance to blood flow due to friction between moving fluid and stationary walls.
Equation for resistance
Resistance =8Ln/pir^4
Where l is length r is radius and n is blood viscosity
What does increasing BP do to pressure gradient, resistance of the vessel and flow to capillaries?
- Increases pressure gradient
- No change to resistance of the vessel
- Increases flow to capillaries
- What does arteriolar vasoconstriction do to pressure gradient, resistance of the vessel and flow to capillaries?
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- No change to pressure gradient
- Increase in resistance of the vessel
- Decrease in flow to capillaries
How do work out flow rate of blood
F=mean arterial pressure/change in pressure gradient/resistance
Vascular tone
Partial constriction enables alterations to blood flow through constriction and dilation (room to accommodate movements)
What is an increase in blood in response to local need called?
Active hyperaemia
Happens via vasodilation
Increased by o2 usage
- When would vasoconstriction of arterioles happen?
If blood temp dropped or stretch increased (distension) due to increased bp- called myogenic autoregulation
Small intestine arterioles undergo myogenic vasoconstriction
- Help regulate systemic arterial blood pressure e.g. maintain bp at 120/80- what is this regulated by?
Extrinsic controls which travel via nerves or blood and are usually centrally coordinated
Such as avp angiotensin I
- What equation links mean arterial blood pressure, cardiac output and total peripheral resistance
Blood pressure (MAP)=cardiac output times total peripheral resistance
Capillary size
7 micrometers diameter
1 micrometer cell width
Why is capillary density important?
So that they are ideally suited to enhance diffusion through Fick’s law
This is through minimising diffusion distance and maximising SA and time for diffusion
Which tissues have denser capillary networks?
Highly metabolically active tissues have denser capillary networks
- What is the structure of capillaries (diagram)?
Cells have small H2O-filled gap junction between them but vessel still called continuous
Cells are covered with basement membrane which is continuous
Some cells have holes called fenestrae which allow >80nM things to pass through- these still have continuous basement membrane though which the things will have to deal with
What are discontinuous capillaries like?
They have fenestrae but also breaks in basement membrane
Common in liver- liver also has sinusoids (sinusoidal capillaries) which are discontinuous structures
What type of capillary is blood brain barrier
Continuous- protects brain as it only allows things to enter which we want
Neonates and premature babies have much leakier BBB so more susceptible to CNS infections secondary to infection in blood
Bulk flow
A volume of protein-free plasma filters out of capillary by hydrostatic pushing force, mixes with surrounding interstitial fluid (IF) and is reabsorbed by capillaries by oncotic pulling force due to higher conc of plasma proteins in vessels
- What are the hydrostatic and oncotic pressure like at the arteriole and venule ends of capillaries?
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Ultrafiltration occurs when pressure inside the capillary is greater in interstitial fluid and reabsorption occurs when there is a negative hydrostatic pressure
Lymph vessels
Are discontinuous
Lymph drains into thoracic duct and right and left subclavian veins
3L travels per day