microcirculation Flashcards
what does each individual organ have
it’s own microcirculation
which branches off the main artery an rejoins to main vein
what does the 1st order arteriole do
lots of smooth muscle
deliver blood to capillaries (where exchange takes place) across organ/tissue
goes to venule > drains to main vein
what is the overall aim of the cardiovascular system
to get adequate blood flow through the capillaries
what is blood flow rate
volume of blood passing through a vessel per unit time
what is Darcy’s law
fluid circuit
change in pressure gradient = flow rate x resistance
Q = pressure gradient / resistance
equation for pressure gradient (change in P)
pressure gradient = pressure A - pressure B
what is flow rate directly proportional to
pressure gradient
what is flow rate inversely proportional to
resistance
what is the definition of resistance
hindrance to blood flow due to friction between moving fluid and stationary vascular walls
what is the equation for resistance
R = 8Ln/pi r^4
vessel length = L
vessel radius = r halving the radius decreases the flow 16 times
blood viscosity = n
only the radius really changes minute to minute - the rest are fairly constant
what happens to pressure gradient and flow rate when increased BP
pressure gradient goes up
flow rate goes up
what happens to resistance and flow rate with arteriolar vasoconstriction
resistance goes up
flow rate goes down
what is mean arterial pressure (number)
93 mmHg
pressure in arteries same amount around the body
what is blood flow of an organ is dependent on
pressure gradient
using pressure B as the pressure leaving the organ (venule)
if flow rate cannot be the same for each organ - what does this indicate about the resistance for each organ
considering pressure entering and leaving are the same for each organ - the resistance must change significantly
without this pressure difference, blood would not reach capillary beds
what does vasoconstriction do to radius, resistance and flow rate
radius decreases
resistance increases
flow rate decreases
(contraction)
what does vasodilation do to radius, resistance and flow rate
increase radius
decrease resistance
increase flow rate
(relaxation)
what does vascular tone mean
partial constriction of arteriolar smooth muscle
this way you can either constrict further or dilate (if completely dilated then you can only constrict) -
in a state of partial constriction you can both dilate and constrict to increase or decrease blood flow
what are 2 reasons why radii of arterioles are adjusted independently
1) to match blood flow to the metabolic needs of specific tissues (depending on bodys momentary needs)
2) to help regulate systemic arterial blood pressure
describe ACTIVE HYPERAEMIA
regulated by intrinsic controls and is independent of nervous or endocrine stimulation
ACTIVE HYPERAEMIA
1) tissue is doing more
2) using more oxygen
3) generates metabolites (influences and is detected by arterioles)
4) arterioles dilate
describe MYOGENIC AUTOREGULATION
MYOGENIC AUTOREGULATION
1) damage to tissue
2) leakage of fluid
3) ice pack/decreased blood temp
4) vasoconstriction - diverting blood away from cold area to preserve body temp
increased stretch (distension) due to high BP > myogenic autoregulation
use exercise as an example to describe matching blood flow to meet demands
perfusion pressure - pressure through tissue bed
1) start exercise
2) pressure increases (good in some tissue but in most = not)
3) increased pressure leads to increased flow to that tissue
4) immediate increase in flow stretches arterioles
5) the arterioles respond to physical stretch
6) cause local constriction called AUTOREGULATION to bring the pressure/flow down
equation for blood pressure
cardiac output (Q) = blood pressure (MAP) / total peripheral resistance (TPR) so blood pressure (MAP) = cardiac output (Q) x total peripheral resistance (TPR)
definition of cardiac output
amount of blood flowing through system
