Lecture 14-Capillary Exchange Flashcards
How do the capillaries provide a short distance for diffusion
thin walls-Thin walls (1µm)
Small diameter (8µm)
Close proximity to cells
why does blood flow slowly in capillaries
large cross-sectional area of capillary network
how does the capillary have a large surface area for exchange
10+ billion capillaries
600m^2
what are the 3 types of capillaries
continuous
fenestrated
sinusoid
which is the most common capillary
continuous
where are fenestrated capillaries found
endocrine organs, intestine and kidneys
features of fenestrated capillaries
water-filled pores to allow rapid change of water and solutes
where are sinusoid capillaries found
endocrine organs, liver, bone marrow, spleen
features of sinusoid capillaries
large clefts between endothelial cells and incomplete BM to allow free exchange of water and larger solutes e.g. plasma proteins
what are the transport mechanisms in capillary exchange
diffusion (down conc gradient)
bulk flow (down pressure gradient)
transcytosis (by vesicular transport; through endothelial cells)
what substances travel through endothelial cells via diffusion in capillary exchange
-lipid soluble gases and molecules e.g. O2, CO2, Fatty Acids
-ions e.g. Na+, K+, Ca2+,Cl- (via ion channels in the ECs)
what substances travel between endothelial cells in capillary exchange
small water-soluble molecules e.g water, ions, glucose, urea, amino acids
what substances travel via transcytosis in capillary exchange
macromolecules e.g glycoproteins in vesicles
where does bulk flow occur during capillary exchange
down pressure gradients between gaps and pores
what is bulk flow associated with in capillary exchange
filtration and reabsorption
what determines bulk flow between capillaries and interstitial fluid
the net pressure difference across capillary walls
what 4 forces influence fluid and solute movement
-capillary hydrostatic pressure
-interstitial fluid hydrostatic pressure
-blood colloid osmotic pressure
-interstitial fluid colloid osmotic pressure
capillary hydrostatic pressure
the blood pressure exerted on capillary walls ‘pushing’ fluid out
interstitial fluid hydrostatic pressure
the pressure exerted on the outer capillary walls by the IF pushing fluid in
blood colloid osmotic pressure
the plasma osmotic pressure pulling the fluid in
interstitial fluid colloid osmotic pressure
the osmotic pressure of the interstitial fluid pulling fluid out
net filtration pressure formula
net filtration pressure= net hydrostatic pressure - net osmotic pressure
net hydrostatic pressure formula
capillary hydrostatic pressure (decreases along capillary) - interstitial fluid hydrostatic pressure (generally negligible- 0)
what does net hydrostatic pressure favour
favours pushing fluid from capillary to IF
net osmotic pressure
blood colloid osmotic pressure - interstitial fluid colloid osmotic pressure
what is blood colloid osmotic pressure affected by
blood volume
why is interstitial fluid colloid osmotic pressure generally negligible
IF has few plasma proteins in suspension
what does a positive net filtration pressure lead to
filtration
what does a negative net filtration pressure result in
reabsorption
what are the values of capillary hydrostatic pressure from the arterial to the venous end
35 -> 18mmHg
what is the value of blood colloid oncotic pressure along the capillary
25mmHg
what gets filtered out of the capillaries
nutrients to tissues
what gets absorbed into the capillary
waste from tissues
what volume of substance is filtered per day
24L/day
how many litres of filtration is delivered to the lymphatic system
3.6 L/day
how many liters of filtration gets reabsorbed
20.4L/day
max filtration pressure is greater than…
max absorption pressure
transition point
filtration is equal to absorption
where is the transition point in capillary exchange located
towards the venous end
what is the effect of hypertension on net filtration pressure
-increased capillary
-hydrostatic pressure
-increased net filtration
-fluid collects in extremities
-systemic oedema
effect of severe hemorrhage on net filtration pressure
-lower CHP
-decreased net filtration pressure
-increased reabsorption
-fluid recalled from tissue into the bloodstream
-increased BP and CO
effect of dehydration on net filtration pressure
-increased blood colloid oncotic pressure
-reduced net filtration pressure
-fluid recalled from tissue into bloodstream
-delays onset of symptoms
effect of tissue damage on net filtration pressure
-increased ICOP as plasma proteins leak into IF
-increased net filtration pressure
-local swelling (oedema)
in pulmonary circulation, what occurs when O2 level falls? How does this differ to other organ vessels
-arterioles constrict in regions of low O2 to shunt blood flow to O2 rich areas
-Enhances O2 absorption
-in other organs, vessels dilate when oxygen levels fall (enhances o2 delivery)
how many alveoli does pulmonary circulation supply
Pulmonary circulation supplies >300 million alveoli
why is pulmonary vascular resistance very low
Arterioles are shorter, wider and have thinner walls
CHP in pulmonary circulation compared to systemic circulation
10 mmHg rather than 35 mmHg
why are arteries more distensible in pulmonary circulation
Can accommodate increased CO with little increase in pressure
what happens if pulmonary CHP exceeds 25mmHg
fluid leaks into alveoli impacting respiration causing pulmonary oedema
what does SNS/ adrenaline cause in the coronary circulation? How does this differ to other organs?
promotes coronary artery vasodilation increasing coronary flow
-in other organs, this would cause vasoconstriction
why is coronary blood flow restricted during systole
due to compression of the left coronary artery
when is coronary flow the highest in the cardiac cycle
during diastole, enabled by arterial elastic recoil
how does coronary circulation compensate for loss of blood flow during systole
Cardiomyocytes have high O2 reserves
The myocardium has high capillary density → increases O2 extraction
in neural emergencies does vasodilation or vasoconstriction occur in cerebral vessels
vasodilation
how much co2 does the brain consume for 2% body mass
12%
flow rate of the brain
750ml/min
do neurons have good or bad metabolic reserves
bad
how many arteries are used to supply the brain
4 arteries that anastomose inside the cranium to maintain flow is there is a disruption
