pulmonary and systemic oedema Flashcards
what are capillaries?
- single layer of endothelial cells
- allows for exchange
- delivery of nutrients and O2 to the cells
- removal of metabolites
- blood flow in the capillaries depends on the contractile state of the aterioles
what is the role of terminal arterioles?
- they regulate regional blood flow to the capillary bed in most tissues
what is the role of precapillary sphincters?
- they regulate flow in few tissues eg mesentery
why is blood flow through capillary bed slow?
- to allow adequate time for exchange
do plasma proteins leave the capillaries to go into the interstitial?
- no
which substances go through the endothelial cells?
- lipid soluble substances
which substances go through the water filled pores?
- water soluble substances
what is transcapillary fluid flow?
- passively driven by pressure gradients aross the capillary wall
- it is ultra-filtration
- forces favour filtration
- A filtration coefficient also affect net fluid filtration
what is ultra filtration?
- exchange across the capillary wall of essential protein-free plasma
what forces favour filtration? (starling forces)
- Pc = capillary hydrostatic pressure
- PiI = interstitial fluid osmotic pressure
which forces oppose filtration? (starling forces)
- PiC = capillary osmotic pressure
- Pi = interstitial fluid hydrostatic pressure (-ve in some tissues)
how is NFP calculated?
- (PC + PieI) - (PieC + Pi)
what are the major forces involved in systemic transpcapillary fluid flow - favouring filtration?
- Pc = capillary hydrostatic pressure
what are the major forces involved in systemic transpcapillary fluid flow - opposing filtration?
- PieC = capillary osmotic pressure
what is oedema?
- accumulation of fluid in interstitial space
- diffusion distance increases - gas exchange compromised in pulmonary oedema
what are the causes of oedema?
- raised capillary pressure
- reduced plasma osmotic pressure
- lymphatic insufficiency
- changes in capillary permeability
how does raised capillary pressure cause oedema?
- arteriolar dilation
- raised venous pressure
- LVF - pulmonary oedema
- RVF - peripheral oedema (ankle, sacral)
- prolonged standing - swollen ankles
how does reduced plasma osmotic pressure cause oedema?
- normal = 65-80
- oedema if <30
- malnutrition
- protein malabsorption
- excessive renal excretion of protein
- hepatic failure
how does lymphatic insufficiency cause oedema?
- lymph node damage
- filariasis - elephantiasis
how do changes in capillary permeability cause oedema?
- inflammation
- histamine increases leakage of protein
what is pulmonary oedema?
- accumulation of fluid in the interstitial and intra alveolar lung spaces
- manifested clinically by SOB
- may be crepitations in auscultations of lung bases
- CXR shows haziness in perihilar region
