Fluid Shift Across the Capillary Wall

Question 1

What is the function of interstitial fluid?

Answer 1

Bathes the body cells

Acts as a go-between blood and body cells

Question 2

How are lipid soluble (e.g. O2, CO2) substances transported across the capillary wall?

Answer 2

Through endothelial cells

Question 3

How are small, water soluble substances (e.g. Na+, K+, glucose, amino acids) transported across the capillary wall?

Answer 3

Through the pores between endothelial cells

Question 4

How are exchangeable proteins transported across the capillary wall?

Answer 4

Vesicular transport

Question 5

How are plasma proteins transported across the capillary wall?

Answer 5

Generally cannot cross the capillary wall

Question 6

What is the net filtration pressure?

Answer 6

Forces favouring filtration - forces opposing filtration

Also affected by net fluid filtration

Question 7

Which forces favour filtration in transcapillary fluid flow?

Answer 7

Capillary hydrostatic pressure

Interstitial fluid osmotic pressure

Question 8

Which forces oppose filtration in transcapillary fluid flow?

Answer 8

Capillary osmotic pressure

Interstitial fluid hydrostatic pressure

Question 9

What happens to the capillary hydrostatic pressure as you move down a capillary?

Answer 9

Decreases from the arteriole to venule end

Question 10

What are the significant forces involved in transcapillary fluid flow?

Answer 10

Capillary hydrostatic pressure

Capillary osmotic pressure

Question 11

What is the net filtration pressure at the arteriolar and venular end of a capillary?

Answer 11

Arteriolar = +10mmHg
Venular = -8mmHg

Question 12

What overall affect do the Starling Forces have on fluid shift in a capillary?

Answer 12

Favours filtration at the arteriolar end (fluid is forced out of the capillary into the interstitium)
Favours reabsorption at the ventral end (fluid is forced into the capillaries from the interstitium)

Question 13

How is excess fluid returned to the circulation?

Answer 13

Via lymphatics as lymph

Question 14

Why dos excess fluid accumulate in the interstium?

Answer 14

Filtration rate exceeds reabsorption (10 out 8 in)

Question 15

What is oedema?

Answer 15

Accumulation of fluid in the interstitial space

Question 16

How does pulmonary oedema affect the lungs?

Answer 16

Diffusion distance increases -> compromised gas exchange

Compliance of the lungs is restricted -> breathlessness

Question 17

What are the main causes of oedema?

Answer 17

Raised capillary pressure
Reduced plasma osmotic pressure
Lymphatic insufficiency
Changes in capillary permeability

Question 18

What can cause a raised capillary pressure?

Answer 18

Arteriolar dilatation
Raised venous pressure =
LVF, RVF, prolonged standing

Question 19

What form of oedema is caused by left ventricular failure?

Answer 19

Pulmonary oedema

Question 20

What form of oedema is caused by right ventricular failure?

Answer 20

Peripheral oedema

i.e. ankle, sacral etc.

Question 21

What form of oedema is caused by prolonged standing?

Answer 21

Swollen ankles

Question 22

What can cause a reduced plasma osmotic pressure?

Answer 22

Malnutrition
Protein malabsorption
Excessive renal excretion of protein
Hepatic failure

Question 23

How does a reduced plasma osmotic pressure cause oedema?

Answer 23

The forces opposing filtration and drawing the fluid back into the capillaries are lost

Question 24

What can cause lymphatic insufficiency?

Answer 24

Lymph node damage

Filariasis - elephantiasis

Question 25

Why do you not see pitting oedema in lymphatic insufficiency?

Answer 25

Pitting oedema is caused by fluid moving back into the lymphatics
Fluid cannot move if lymphatics are not working correctly

Question 26

What can cause changes in capillary permeability?

Answer 26

Inflammation

Histamine increases leakage of protein