Microcirculation Flashcards
(40 cards)
What is the overall aim of the CVS?
Adequate blood flow
through the capillaries
What is the microcirculation?
- Arterioles
- Capillaries
- Venules
What is blood flow rate?
Volume of blood passing through a vessel per unit time
How do you calculate flow rate?
Q (flow rate) = Pressure gradient / Resistance
What is pressure gradient?
Pressure gradient (DP) = Pressure A – Pressure B
What will an increase in pressure gradient do?
Increase flow rate
What is resistance?
Hindrance to blood flow due to friction between moving fluid and stationary vascular walls
What impacts resistance?
- Vessel length
- Vessel radius (changes)
- Blood viscosity
What happens in increased blood pressure?
Pressure gradient: increase
R:
F: increase
What happen in arteriolar vasoconstriction?
Pressure gradient:
R: increase
F: decrease
When is the biggest pressure difference?
One end of arteriole to another
How do you calculate flow rate for an organ?
Forgan = pressure gradient (MAP) / Rorgan
-Without this pressure difference blood would not reach tissue capillary beds
What happens in vaso contraction?
r: decrease
R: increase
F: decrease
What happens in vasodilation?
r: increase
R: derease
F: increase
-
Why is vascular tone important?
- Arteriolar smooth muscle normally displays a state of partial constriction (this is vascular tone)
- If you need capacity to both dilate and contract (can contract further or dilate)
How many ways can radii of arterioles adjust independently?
Radii of arterioles are adjusted independently to accomplish two functions
What is the first function? How is this regulated?
- Function 1: Match blood flow to the metabolic needs of specific tissues (depending on body’s momentary needs)
- Regulated by local (intrinsic) controls and independent of nervous or endocrine stimulation
What is the second function? How is this regulated?
- Function 2: Help regulate systemic arterial blood pressure
2 Regulated by extrinsic controls which travel via nerves or blood and are usually centrally coordinated
How does the arterioles match blood flow to the metabolic needs of specific tissues (depending on body’s momentary needs) chemically?
- If more active: function may be chemically driven
- increase metabolites + O2 usage
- Therefore vasodilation of arterioles (tissue dilates)
- Called active hyperaemia
How does the arterioles match blood flow to the metabolic needs of specific tissues (depending on body’s momentary needs) physically?
- function may be physically driven
1. Decrease blood temp
2. Increase stretch (distension) due to increase BP - Therefore vasoconstriction of arterioles
- Called myogenic auto regulation
What happens if BP increases?
- Flow to nay tissue bed increases
- As blood flow increases it stretches
- If tissue realises it doesn’t need this responds and contracts
- To ensure that blood doesn’t increase to every tissue
In exercise what happens?
- Skeletal muscle arterials go to active hyperaemia
2. Small intestine arterioles go toward myogenic vasoconstriction
Generate and equation for flow across the whole circulation and rearrange to generate a BP equation?
Cardiac output (Q) = Blood pressure (MAP) / totally peripheral resistance (TPR)
How do arterioles help regulate arterial blood pressure (centrally)?
- Cardiovascular control centre in medulla (e.g. loss of blood) for vasoconstriction (to maintain BP)
- This would decrease blood flow to specific organs as vasoconstriction decrease flow
- Brain is no1 💓
