Oedema

Question 1

What are the two main pressures at work in the kidney?

Describe what they do?

Answer 1

Hydrostatic pressure: forces fluid out of the capillaries into interstitial space (surrounding cell) (like squeezing a balloon with a hole in it). Higher the BP, higher hydrostatic pressure

Oncotic pressure: pressure exerted by protein (albumin) in the bloodstream. Water wants to be where protein is, so protein in bloodstream keeps water in bloodstream

Question 2

Mechanism of oedema?

Answer 2

Misbalance between hydrostatic and oncotic pressure

Low oncotic pressure, due to fewer proteins in the blood, will mean there is less force keeping water in the vessels. It will leak out into interstitial space causing oedema

OR

High hydrostatic pressure, higher blood volume (blood backing up due to heart failure) means more fluid forced out of capillaries and into interstitial space

Question 3

What are the causes of oedema?

Explain!

Answer 3

Reduced oncotic pressure due to reduced serum protein / albumin

• reduced production in liver dysfunction
• loss of protein in kidney dysfunction, meaning less is in blood stream

Raised hydrostatic pressure due to higher blood volume
- in RHF, blood backs up into venous system, which means blood backs up into capillaries. There’s more blood there so higher volume, so higher hydrostatic pressure