Microcirculation Flashcards
features of the microcirculation
1st order arteriole with smooth muscle (bring substances to capillaries)
terminal arteriole
precapillary sphincter
capillaries (exchange)
pericytic venule
venule (substances deposited then blood leaves the tissue)
microvasculature differences between organs
specific to each organ
aim of CVS
adequate blood flow through the capillaries
what is the blood flow rate
volume of blood passing through a vessel (and to the tissue) per unit time
what is Darcy’s law
pressure gradient = flow rate *resistance
flow rate =
pressure gradient/resistance
pressure gradient =
pressure A - Pressure B
where is pressure A and B
A - start of arteriole
B leaving arteriole - determines how much blood flows through the capillaries
affect of increasing pressure gradient
increase blood flow
what is resistance
Hinderance to the blood flow due to friction between moving fluid and stationary vascular walls
variation in vessel length and blood viscosity
very slow changes
variation in vessel radius
change in seconds - has a major effect on resistance
affect of increasing blood pressure on pressure gradient, resistance and flow
P - increase
R - no change
F - increase
affect of arteriolar vasoconstriction on pressure gradient, resistance and flow
P - no change
R - increase
F - decrease
MAP entering arterioles
99mmHg
MAP leaving arterioles
37mmHg
affect of arterioles
huge pressure drop from 1 side to the other
pressure gradient in arterioles
pressure in = MAP
out - low mmHg
therefore pressure gradient = MAP
without it - blood wouldn’t reach capillaries
in arterioles flow(organ) =
MAP/R(overall)
affect of contraction on radius, resistance and flow
r - decrease
R - increase
F - decrease
affect of relactation on radius, resistance and flow
r - increase
R - decrease
F - increase
why does arteriolar smooth muscle normally display partial contraction
so either further dilation/contraction can take place
why are the radius of arterioles changed
1 - match blood flow to metabolic needs - intrinsic controls, main function. Each tissue regulate arteriolar muscle based on conditions in that tissue
2 - help regulate systemic arterial pressure - extrinsic control via nerves/blood
how are chemicals used to match blood flow to metabolic needs
there is an increase in metabolite production and oxygen usage
bv react to local change
more blood flow - vasodilation
ACTIVE HYPERAEMIA
how is blood flow matched to metabolic needs using physical methods
decrease in temp/increase in stretch due to increase in bp
reduce flow to skin arterioles
eg add cool to stop swelling
MYOGENIC AUTOREGULATION
effect of autoregulation when Bp is increased
there is a change in pressure gradient in every tissue - not enough blood to perfuse all of the tissues
with no autoregulation - flow increases and resistnace decreases
with autoregulation - R increases and flow decreases
skeletal muscle arterioles response during exercise
active hyperaemia
small intestine arterioles response during exercise
myogenic vasoconstriction
increased pressure - these arterioles don’t need it son reduce the blood flow
CO =
MAP/total peripheral resistance
MAP =
CO*TPR
how do arterioles regulate arterial bp via neurons
nervous and hormonal control
nerves from cardiovascular control centre in the medulla
predominantly cause vasoconstriction
if you vasoconstrict and increase resistance and pressure decreases flow to specific organs
if you lose a lot of blood - vasoconstriction of all vessels - negative consequences if long termn
how do arterioles regulate arterial bp via hormones
ADH(vasopressin), angiotensin II and adrenaline/noradrenaline cause vasoconstriction
other action of Ang II
preserves water
relationship between neuronal and hormonal control of Bp
work together in times of need
focussed on ensuring flow to the brain
what is the purpose of capillary exchange
delivery of metabolic substrates to the cells of the organism
why is capillary density important
ensures that every cell is relatively close to the capillaries
highly metabolic capillaries have denser capillary networks
what are capillaries designed for
to enhance diffusion - Fick’s law
minimise distance
maximise the SA - branching
3 most heavily perfused tissues with capillaries
lung 3500cm2/g
brain/myocardium 500
skeletal muscle 100
what are precapillary sphincters
allow some capillaries to be shut down - eg skeletal muscles have a huge capacity but limited flow at rest, at exercise they take a lot of output
tissue with low capillary density
adipose
describe continuous capillaries
most common
small water filled gap junction
transport through continuous capillaries
if lipid soluble - pass through the cell
if small - pass through gap junction
if big - need mechanism to travel through cell eg channel
describe fenestrated capillaries
filter stuff of a certain size - in glomerulus of kidney
stiff ends up in the urine
P-glycoprotein transporter kick stuff out of the capillaries
if water soluble a mechanism is needed
if really lipid soluble - enter the brain
fenestrae 80nm
location of fenestrated capillaries
glomerulus in kidney
describe discontinuous blood flow
very large gaps
where are there discontinuous capillaries
bone marrow - WBC need to enter blood
liver - need to metabolise lots of things - need substances to be able to easily access liver tissue
type of capillary that forms the blood brain barrier
continuous with tight junctions instead of gap junctions
tighter control of what enters and leaves the cell
what is a leaky blood brain barrier
normal continuous structure
access and sample blood easier
describe fluid movement in capillaries
bp force fluid through capillaries
fluid squeezed into tissues
protein free plasma leaves the bv, mixes with interstitial fluid and is reabsorbed - bulk flow
if lost all blood vol and pressure would decrease so need counter force to draw fluid in
oncotic pressure in blood (plasma proteins) not in interstitial fluid
starling’s forces
what does the hydrostatic force do
push out of the capillaries
what does the oncotic force do
pull into the capillaries
osmotic oressure caused by proteins
explain the balance between hydrostatic and oncotic forces
if pressure in capillary is bigger than in interstitial fluid - untrafiltration - ie fluid out
if inward driving pressure hogher than outward driving pressure - reabsorption - fluid in
why is oncotic pressure stable
protein composition doesn’t change
change in hydrostatic pressure down the capillary
it decreases
what is the result of ultrafiltration being more effective than reabsorption
always losing blood from the system
without mechanism fluid would be lost
role of lymphatic system
change of 1
describe the lymphatic system
wherever a blood capillary is there is a lymphatic capillary
lymph capillaries are blind ending
fluid diffuses into a lymphatic flap - allow fluid in but don’t let it out
features of the lymphatic system
lymphatic endothelium anchoring filament interstitial fluid opening lymphatic capillary
other role of lymphatic system
immune surveillance mechanism
fluid through lymphatic system - stimulate lymphocyte production in lymph nodes
structure of the lymphatic system
no pump for flow
drain from R lymphatic duct to thoracic duct
and into the R and L subclavian valves
here there is a close connection to vein - deposit in the venous system
3L a day
limitations with the lymphatic system
if rate of production of fluid is highe than the rate of drainage - then oedema
elephantiasis - parasitic blockage of lymph node
tissue damage - inflammation, capillaries leakier, more fluid is forced into the tissue so can’t be drained properly
how does vessel length increase resistance
more of the vessel for the blood to make contact with
what is cardiac output
blood flow - amout of blood out
what in total peripheral resistance
store of resistance in every tissue - total resistance in system
