Fluid shift across capillary wall (wk5)

Question 1

What is interstitial fluid?

Answer 1

Extracellular fluid that bathes the cells of the body.

Question 2

How thick is a capillary? what is its function?

Answer 2

One cell thick

Exchange of gasses and nutrients with the interstitial fluid.

Question 3

What substances can or cannot and how do they pass through the capillary wall?

Answer 3

• Lipid soluble substances move through endothelial cells.
• Small water soluble substances pass through pores.
• Exchangeable proteins move by vesicular transport
• Plasma proteins cannot move across capillary wall

Question 4

What laws do fluid and gas movement follow?

Answer 4

• fluid : follows pressure gradient

- Gasses : follow Ficks law of diffusion (partial pressure difference)

Question 5

What happens in fluid flow in the capillary?

Answer 5

Follows Pressure gradients across the capillary wall.

Ultra filtration process- exchange of protein free plasma.

Question 6

What are the forces favouring/ opposing capillary flow?

Answer 6

1. For
   - Capillary hydrostatic pressure (pressure generated by fluid on capillary wall)
   - interstitial fluid osmotic pressure (pressure exerted by proteins in interstitial fluid)
2. Against
   - Interstitial fluid hydrostatic pressure
   - Capillary osmotic pressure

Question 7

What are the Net filtration pressure values in the arteriolar and venous ends? (+/-?)

Answer 7

1. Arteriolar= +, filtration

2. Venous= -, reabsorption.

Question 8

What happens to excess fluid?

Answer 8

Drains into lymphatic system as lymph.

Question 9

What is different about pulmonary capillaries that helps prevent fluid build up?

Answer 9

Efficient lymphatic drainage- removes any filtered fluid in the lungs out as lymph. prevents accumulation of interstitial fluid.

Question 10

What happens in pulmonary oedema?

Answer 10

Build up of fluid in interstitial space. Gas exchange compromised

Question 11

What are the causes of oedema?

Answer 11

1. Raised capillary pressure: arteriolar dilatation, raised venous pressure.
   LVF- Pulmonary oedema
   RHF- Systemic oedema.
   Prolonged standing- swollen ankles
2. Reduced plasma osmotic pressure- malnutrition, protein malabsorption, excessive protein excretion, hepatic failure.
3. Lymphatic insufficiency- lymph node damage, filariasis
4. Changes in capillary permeability- inflammation, histamine leakage of protein.

Question 12

What is the main symptom of Pulmonary odema?
What can be heard on clinical examinations?
What does the CXR show?

Answer 12

SOB
Crepitations in lung bases
Haziness in perihilar region