Microcirculation Flashcards
What are the parts of the microcirculation?
1st order arteriole
terminal arteriole
pericytic venule
venule
capillaries
precapillary sphincter
smooth muscle
What is the overall aim of the cardiovascular system?
adequate blood flow through the capillaries
What is blood flow rate?
volume of blood passing through a vessel per unit time
How do you calculate flow rate?
Q= deltaP/ resistance
flow rate= pressure gradient/ resistance
What is the pressure gradient?
What is resistance?
Hindrance to blood flow due to friction between moving fluid and stationary vascular walls
How do you calculate resistance?
R= 8L/ r^4
l= vessel length
r= vessel radius
it can also be R= (8 x n x L)/ r^4
n= blood viscosity
What happens when you halve the radius?
flow decreases x16
What happens to pressure, resistance and flow when blood pressure increases?
pressure increases
flow increases
What happens to pressure, resistance and flow when there is arteriolar vasoconstriction?
resistance increases
flow decreases
Where does the biggest pressure drop occur?
between arterioles
What regulates the pressure within the system?
arterioles
How do you calculate flow in an organ?
What is special about the pressure gradient in tissues?
They are all the same
- only resistance varies
- it determines flow
What happens if there is no pressure difference?
Blood would not reach tissue capillary beds
Why is vascular tone important?
It allows the arteriole to constrict further or dilate
What happens during relaxation/ vasodilation to radius, resistance and flow?
radius increases
resistance decreases
flow increases
What happens during contraction/ vasoconstriction to radius, resistance and flow?
radius decreases
resistance increases
flow decreases
What is vascular tone?
arteriolar smooth muscle normally displays a state of partial constriction- aka the vascular tone
Radii of arterioles are adjusted independently to accomplish two functions, what are these 2 functions?
Function 1: Match blood flow to the metabolic needs of specific tissues (depending on body’s momentary needs)
Function 2: Help regulate systemic arterial blood pressure
How is the “Match blood flow to the metabolic needs of specific tissues (depending on body’s momentary needs)” regulated?
Regulated by local (intrinsic) controls and independent of nervous or endocrine stimulation
How is the “Help regulate systemic arterial blood pressure” regulated?
Regulated by extrinsic controls which travel via nerves or blood and are usually centrally coordinated
Explain in more detail the function “Match blood flow to the metabolic needs of specific tissues (depending on body’s momentary needs)”.
This function may be chemically driven.
Increases metabolites and O2 usage.
Vasodilation of arterioles.
- skeletal muscles dilate to allow more nutrients etc. to a particular tissue
This is called active hyperaemia (chemically driven change)
Explain in more detail the function “Help regulate systemic arterial blood pressure”.
This function may be physically driven.
Decrease blood temperature.
Increase stretch (distension) due to increased BP.
Vasoconstriction of arterioles
- divert blood away
This is called myogenic autoregulation (physically driven change e.g., using an ice pack)
What happens to resistance, flow, perfusion with autoregulation and no autoregulation?
How do you calculate cardiac output?
blood pressure (MAP)/ Total peripheral resistance (TPR)
Q= MAP/ TPR
How does the neural aspect of the arteriole function “help regulate arterial blood pressure” work?
Neural
Cardiovascular control centre in the medulla
Leads to vasoconstriction
Leading to decreased blood flow in specific organs (you want this acutely as this can become dangerous)