Oedema

Question 1

A precapillary sphincter is a band of smooth muscle around the arterioles. What does it do?

Answer 1

regulates blood flow into the capillaries (mainly in the mesenteric microcirculation).

Question 2

net filtration pressure = ____ - _____

Answer 2

forces favouring filtration - forces opposing filtration

Question 3

what is the filtration coefficient?

Answer 3

the permeability of the capillary to fluid

Question 4

what is the osmotic pressure of a solution?

Answer 4

the pressure by which water is drawn into it through the semi-permeable membrane: the more concentrated the solution, the greater the osmotic pressure

Question 5

what are the 2 forces favouring filtration in the circulation?

Answer 5

hydrostatic pressure of the capillaries

osmotic pressure of the interstitial fluid

Question 6

what are the 2 forces opposing filtration in the circulation?

Answer 6

hydrostatic pressure of the interstitial fluid

osmotic pressure of the capillary

Question 7

Starling forces favour filtration / reabsorption at arteriolar end?

Answer 7

filtration

Question 8

Starling forces favour filtration / reabsorption at venular end?

Answer 8

reabsorption

Question 9

what are the two major forces that contribute to NFP?

Answer 9

capillary osmotic pressure and capillary hydrostatic pressure

Question 10

more fluid is filtered than reabsorbed. Where does the excess fluid go?

Answer 10

returns to circulation as lymph

Question 11

what is special about the pulmonary resistance and the pulmonary capillary hydrostatic pressure?

Answer 11

the pulmonary resistance and pulmonary hydrostatic pressure are very low. Capillary osmotic pressure is higher than hydrostatic –> resulting in efficient lymphatic drainage, preventing accumulation of interstitial fluid

Question 12

causes of oedema?

Answer 12

• raised capillary pressure (due to arteriolar dilatation, raised venous pressure due to LV failure - pulmonary oedema, RV failure (peripheral oedema), prolonged standing (swollen ankles))
• reduced plasma osmotic pressure (oedema is plasma proteins are low due to e.g. malnutrition, protein malabsorption, excessive renal excretion of protein, hepatic failure)
• lymphatic insufficiency (lymph node damage, filariasis (parasitic infection)
• change in capillary permeability (inflammation, histamine increases leakage of protein)