Microcirulation Flashcards
what is the point of microcirculation — what are capillaries
3 forces of material exchange
where are capillaries highest? least?
point of ciruclation –> get O2 and nutrients while removing waste and CO2
- this process is best conducting at the capillary–> where these is thin areas of 1cell thick for passing
capillaries: made of endothelium approx. 5-10 micrometers (1 rbc size!)
how is material exchanged?
1. diffusion
2. filteration
3. absorption
highest capilarry density?
- in striated muscle (where they’re working & need more nutrition!!) – heart, skeletal muscle
lowest?
- connective tissue, subcut. fat & cartilage
how is blood flow to the capillary determined?
- what is the PRIMARY determinant factor?
we know blood flow is not uniform – depending on demand, need, etc. there is change in blood flow
but blood from TO a capillary is primarily dependednt on the arteriole contractile (or dialted) state!!!
- the post-capillary flow can play role too — like in CHF, backup, leading to edma – but the primary reason is the arteriole flow in (high pressure systems with low velocity!!)
what is the difference between nutrtional and non-nutritional flow?
nutritional flow: blood flow that parcipitates with gas excahange and exchange of soultes (proteins) from plasma to tissue
non-nutrtional flow: flow that is due to “shunting” or bypassing a specific area
– think about blood flow to teh gut during SNS stimulation –> you’re going to bypass blood (low metabolic activity)
the pre-capillary vessel closes– shunts blood around
types of capillaries
continuous: virtually no gaps – only allows ionsand other small particles to diffuse
- this is in muscle, fat and lungs
fenstrated: capillaries with intercellular gaps: allowing for exchange of some larger particles – think like proteins
- this is kidney, GI, glands
discontinuous: large gaps with a discontinuous basement membrane – allows whole cells to escape
- see in the bone marrow, liver and spleen
how does intracapillary pressure change
- at rest
- during arteriolar constriction
- during dialation
at rest
p(in) - 25
p(out) - 12
during constriction
p(in) - 12
p (out) - 8
(less of a difference in pressure leads to less flow through)
during dilation (the difference in pressures will increase allowing for a greater flow)
p(in) - 40
p(out) - 25
how are capillaries about to withstand such high pressures if need be?
how is the pressure inside a capillary determined?
small radius = small tension = small pressure!
- able to maintain the pressures (although not crazy high) still maintained becuase the capillaries are so small – so there is not much tension (on the wall)
if you increase the radius (think about the aorta) – then youll have a greater tension force on the wall – therefore a greater pressure on the wall (less velocity through)
how is pressure determined in the capillary?
- well the flow in = flow out
- the capillary is so small – that it increases resistance to the flow –> so that the flow decreases
what is the passive role of endothelium in capillary exchange?
(not the constriction and relaxation)
discuss diffusion of lipid soluable and water soluable things
we have to think about osmotic and hydrostatic pressures here too!
- the small molecules will equlibriate between a capillary and the interstitum
- but the proteins will not!! higher protein in the blood than interstitium
Lipid-soluable (non-polar)
- things like O2 and CO2 can DIFFUSE directly across the membrane walls
water-soluable (polar)
- they wont be able to pass through via simple diffusion
- need a PORE or channel to allow them through
- water, glucose, Na+
- but there are so many pores that this happens easily
permiability through a pore is determiend by size
concentration and difusion
-flow-limited diffusion vs.
-diffusion-limited
high to low concentration is how things diffuse
- small molecules are “flow limited” meaning how much blood is getting to whatever tissue is the only factor in determining how theyre able to diffuse
- larger molecules are diffusion limited – meaning that they NEED the pore to diffuse – doesnt matter how much (volume) of the blood is there – if there arent pores they cant
physiologic factors which control the rate of “diffusion” therefore absporbtion and filteration of solutes
filteration v. absorbtion
what forces play a role
filteration: the movement of fluid and solutes OUT of the capillary into the interstital space
absorption: the movement of fluid and solutes INTO the capillary from the interstitial space
Forces
- capillary pressure & interstital pressure = hydrostatic pressure = net force is a movement outwards the water flowing outward to interstitum
- osmotic/collid pressures (of capillary and interstitum) = pressure due to protein = net flow of osmotic pressure is back into the capillary (higher protein concentration in here)
** protein = albumin (globulin lesser extent)
absorption and filteration – should they be equal?
- what are they like in inflammation?
- in shock?
- in CHF?
- in hepatic failure?
under normal conditions: the rate of absorbtion and filteration should be equal
in inflammation = the arteries dialate to let all the inflammatory molecules rush to the site of injury –> increased pressure within the capillary with increased dilation –> there is an increase in filteration out until the interstitum (and minimal flow back to capillary) = net increase filteration to the outside into the insterstitum of fluid
in shock = results in a SUDDEN drop in pressures of the capillaries (becuase poor flow) so there is net absorbtion back into the capillaries = think compensation for volume loss
in CHF: there is back-up of flow (venous volume too high)which results in a high pressure in the capillaries = net flow of filteration into the interstitum = edema!
in hepatic failure: decrease proteins being made and traveling through the blood– less “pull” of oncotic pressure back into the capillaries – net flow out into the interstitum
how is lymph flow able to happen ?
lymph flow occurs because of interstital pressure
- elevated capillary pressure pushes stuff into interstitum –> therefore evenetually increases interstitial pressure and therefore impacting lymph pressure and flow!
the “pump” of lymph
- muscle movement of smooth muscle guide lymph flow
- some valve component in lymph
- external compression and increase lymph flow
