Capillary Solute and Fluid Exchange II Flashcards
Why does fluid move across the membrane into the interstitial space?
Due to blood flow which exerts a hydraulic pressure.
What is oncotic pressure?
An osmotic pressure which creates a suction force to move fluid into the capillary caused by large molecules that can’t pass through the membrane.
What are the 4 pressures that determine filtration rate?
Osmotic pressures - plasma proteins /
- interstitial proteins
Hydrostatic pressures - capillary blood pressure /
- interstitial fluid pressure
Explain the following equation.
Jv = LpA [(Pc-Pi) - sigma(pi p-pi i)]
Jv = net fluid movement
Lp = hydraulic conductance of the endothelium (how leaky it is to fluid)
A = wall area
(Pc - Pi) = hydraulic pressure difference
sigma = reflection coefficient (1 means nothing conducted across capillary wall and 0 means all)
(pi p-pi i) = osmotic pressure difference
In normal conditions Lp and A are constant.
What are typical pressures for: Pc Pi pi p pi i
Pc = 35mmHg
Pi = -1mmHg
pi p = 25mmHg
pi i = 10mmHg
In a well perfused capillary where there is filtration along the entire capillary what is the new equation used to calculate net filtration pressure?
Jv = Pc - [sigma(pi p-pi i) + Pi] where sigma(pi p-pi i) is about 13mmHg
What does the lymphatic circulation do?
How does it do this?
Returns excess tissue fluid/solutes back to the cardio-vascular system
Lymph vessels have valves and SM and there is surrounding skeletal muscle that contributes to lymph flow.
How does the body compensate for low BP in the case of a haemorrhage?
Capillary pressure will drop to almost half - BP drops more as you go along the capillary - reabsorption occurs because pi p stays the same as the conc of proteins is still the same. Reabsorption makes material move from the interstitial space into the circulation. This maintains SV and CO so blood flow is maintained to major organs. Low BP also stimulates symp stimulation which induces vasoconstriction of arterioles - pressure gets less downstream and so reabsorption can occur.
What is oedema?
How is it caused?
Excess of fluid within the interstitial space.
Increased Pc, decreased pi p, inflammatory response, lymphatic problems.
Describe what may happen when you have increased capillary pressure with prolonged orthostasis.
More blood goes into veins in lower limb - DVT/ cardiac failure. DVT may happen in a femoral vein - blockage - prevents venous return from certain area. Blood still enters area but is not drained properly - increase pressure in lower limb - increase back-up pressure leading to increased Pc across capillaries and therefore you will get a net filtration - more fluid in interstitial space and swelling of lower limb.
What is an outcome to the lungs due to left ventricular heart failure?
What is an outcome of right sided heart failure?
Not much blood ejected to body so build-up of pressure in left ventricle which will back up into left atrium and pulmonary vein. This causes capillary pressure to build up in the lungs - extra filtration - pulmonary oedema.
Swelling in limbs - back up of pressure in great veins and venous system of the lower limbs.
What is and happens in Kwashiorkor syndrome?
What other diseases can allow symptoms of this syndrome to occur?
It occurs when a patient has malnutrition - not enough protein in diet so don’t make enough plasma proteins. Low plasma proteins means less oncotic pressure is exerted and so there is less suction force taking fluid from the interstitial space into blood. This means there is more filtration and you get oedema and swelling.
Hepatic failure, nephrotic syndrome
Explain what happens in inflammatory mediated oedema.
Swelling is triggered by local chemical mediators of inflammation. The capillary permeability changes and becomes more leaky. You get contraction of the endothelial cells and so much bigger intercellular spaces. Hydraulic pressure can force fluid out by filtration.
Give 2 names of diseases that occur due to lymphatic obstruction.
How does the obstruction occur?
Filariasis/Elephantitis
Worm infestation - larvae migrate to lymphatic system and form nests which block lymph drainage.
When is lymphatic removal used?
What is a side effect of the surgery?
To treat testicular cancer
Reduced ability of areas in the body to reabsorb the fluid that is filtered.
