Fluid shift across the wall: Pulmonary and Systemic Oedema Flashcards
what proportion of our bodies is extracellular fluid?
1/3 rd roughly
what percentage of ECV is interstitial i.e bathing the body cells
about 75%
where does the exchange of nutrients occur?
at the capillaries
what does the thin capillary wall allow for?
rapid exchange of gases, water and solutes with interstitial
what are the other functions of the capillaries ? 2 things
- removal of metabolites from cells
- delivery of nutrients and oxygen to the cells
what does the blood flow in the capillaries depend on?
the contractile state of the terminal arterioles
In some tissues (e.g. mesentry) there is another component involved in the regulation of flow, wha is this?
the precapilary sphincters
what is the rate of blood flow like in the capillary beds?
very slow to allow adequate time for exchange
which molecules can cross the capillary wall? 3 things - generally
- lipid soluble sustances
- small, water soluble substances
- exchangeable proteins
how are lipid soluble substances moved from the capillaries to the interstitium?
they pass through the endothelial cells
how are small water soluble substances moved from the capillaries to the interstitium?
through the water filled pores between endothelial cells
how are exchangeable proteins moved from the capillaries to the interstitium?
they are moved across by vesicular transport
which molecules cannot generally cross the capillary wall?
plasma proteins
give some examples of the small water-soluble substances that can pass through the pores?
Na, K, Glucose and amino acids
give some examples of the lipid soluble substances that can pass through the endothelial cells ?
O2 and CO2
Fluid movement follows _____
Gradient (bulk flow)
Fluid movement follows Pressure Gradient (bulk flow)
which law does the movement of gases and solutes follow?
flick’s law of diffusion
Transcapillary fluid flow is _____ driven by _____ gradients across the capillary wall
It is called ___ i.e. exchange across the capillary wall of essentially protein-free ___
Transcapillary fluid flow is passively driven by pressure gradients across the capillary wall
It is ultra-filtration i.e. exchange across the capillary wall of essentially protein-free plasma
what is the NPP =
forces favouring filtration (ie movement of fluid from the capillary to the interstitium) - forces opposing filtration
what is the other factor that effects net fluid filtration?
filtration coefficient (kf). Pressure is more important though
what are the two forces favouring filtration just after the arterioles
Pc - capillary hydrostatic pressure
(pi)i interstitial osmotic pressure
what are the two forces opposing filtration just before the venules
(pi)c - capillary osmotic pressure
Pi - interstitial hydrostatic pressure
the main one is the capillary osmotic pressure
NFP = (P_ + π_) - (π_ + P_)
(PC + πi) - (πC + Pi)
Starling forces favour ___ at arteriolar end, ______ at venular end
Starling forces favour filtration at arteriolar end, reabsorption at venular end
what are the major forces involve din systemic transcapillary flow?
Pc and (pi) c
During a day filtration exceeds reabsorption by 2- 4 litres. How is the excess fluid returned to the circulation?
via the lymphatics as lymph
what are the mechanisms to protect the lungs against pulmonary oedema? 4 things
Pulmonary resistance is only ~10% of that of the systemic circulation
Pulmonary capillary hydrostatic pressure is low (~ 8-11 mmHg)
Capillary osmotic pressure at 25 mmHg
Efficient lymphatic drainage remove any filtered fluid thus preventing accumulation of interstitial fluid
what is oedema?
accumulation of fluid in interstitial space
Diffusion
what does pulmonary oedema affect in the lungs? two things
gas exchange and compliance
what are the 4 causes of oedema?
- raised capillary pressure
- reduced plasma osmotic pressure
- lymphatic insufficiency
- changes in capillary permeability
what are the two main causes of raised capillary pressure
- arteriolar dilatation
- raised venous pressure
what three things may cause raised venous pressure?
- LV failure
- Right ventricular failure
- prolonged standing
where is the oedema in LVF?
lungs
where is the oedema in RVF?
peripheral oedema )ankles, sacral)
what is the normal plasma osmotic pressure?
65-80 g/l
what plasma osmotic pressure is required for oedema?
what can cause a low plasma osmotic pressure?
malnutrition
protein malabsorption
excessive renal excretion of protein
hepatic failure
what can cause lymphatic insufficiency?
- lymph node damage
- filariasis - elephantiasis
what kind of oedema is present in lymphatic insufficiency and why?
if someone has a lymphatic obstruction you get non-pitting oedema because you cannot push the fluid back into the lymphatics
what causes changes in the capillary permeability?
inflammation
- histamine increases leakage of protein
what is the symptom from pulmonary oedema?
breathless
wat are the signs of pulmonary oedema?
creps at the lung bases
what does a cxr show in pulmonary oedema?
haziness in perihilar region
