pulmonary and systemic oedema

Question 1

what are capillaries?

Answer 1

• 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

Question 2

what is the role of terminal arterioles?

Answer 2

• they regulate regional blood flow to the capillary bed in most tissues

Question 3

what is the role of precapillary sphincters?

Answer 3

• they regulate flow in few tissues eg mesentery

Question 4

why is blood flow through capillary bed slow?

Answer 4

• to allow adequate time for exchange

Question 5

do plasma proteins leave the capillaries to go into the interstitial?

Answer 5

• no

Question 6

which substances go through the endothelial cells?

Answer 6

• lipid soluble substances

Question 7

which substances go through the water filled pores?

Answer 7

• water soluble substances

Question 8

what is transcapillary fluid flow?

Answer 8

• passively driven by pressure gradients aross the capillary wall
• it is ultra-filtration
• forces favour filtration
• A filtration coefficient also affect net fluid filtration

Question 9

what is ultra filtration?

Answer 9

• exchange across the capillary wall of essential protein-free plasma

Question 10

what forces favour filtration? (starling forces)

Answer 10

• Pc = capillary hydrostatic pressure

- PiI = interstitial fluid osmotic pressure

Question 11

which forces oppose filtration? (starling forces)

Answer 11

• PiC = capillary osmotic pressure

- Pi = interstitial fluid hydrostatic pressure (-ve in some tissues)

Question 12

how is NFP calculated?

Answer 12

• (PC + PieI) - (PieC + Pi)

Question 13

what are the major forces involved in systemic transpcapillary fluid flow - favouring filtration?

Answer 13

• Pc = capillary hydrostatic pressure

Question 14

what are the major forces involved in systemic transpcapillary fluid flow - opposing filtration?

Answer 14

• PieC = capillary osmotic pressure

Question 15

what is oedema?

Answer 15

• accumulation of fluid in interstitial space

- diffusion distance increases - gas exchange compromised in pulmonary oedema

Question 16

what are the causes of oedema?

Answer 16

1. raised capillary pressure
2. reduced plasma osmotic pressure
3. lymphatic insufficiency
4. changes in capillary permeability

Question 17

how does raised capillary pressure cause oedema?

Answer 17

• arteriolar dilation
• raised venous pressure
• LVF - pulmonary oedema
• RVF - peripheral oedema (ankle, sacral)
• prolonged standing - swollen ankles

Question 18

how does reduced plasma osmotic pressure cause oedema?

Answer 18

• normal = 65-80
• oedema if <30
• malnutrition
• protein malabsorption
• excessive renal excretion of protein
• hepatic failure

Question 19

how does lymphatic insufficiency cause oedema?

Answer 19

• lymph node damage

- filariasis - elephantiasis

Question 20

how do changes in capillary permeability cause oedema?

Answer 20

• inflammation

- histamine increases leakage of protein

Question 21

what is pulmonary oedema?

Answer 21

• 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