Exchange and the lymphatic system

Question 1

Characteristics of the capillaries

Answer 1

1 cell thick
large SA:V ratio
short diffusion pathway
exchange system

Question 2

Different types of capillaries

Answer 2

Continuos: No cleft or channels e.g. brain or just Clefts e.g. muscle
Fenestrated: Many clefts and channels in large exchange systems e.g. kidneys and intestines
Discontinuos: very very large channels e.g. liver

Question 3

Different exchange systems?

Answer 3

Diffusion: non-polar can diffuse straight across
Carrier-mediated e.g. glucose
BULK FLOW:
Hydrostatic/oncotic pressure:
-close to arterioles there is a higher hydrostatic pressure inside the cells- higher water content- so water flows out
-closer to veins there is a higher oncotic pressure- higher concentration of proteins- so water flows back in
-20 litres lost
-17 litres regained
-3 enter the lymph system

Question 4

pathologies of the lymph system:

Answer 4

LIQUID LOST IN PERIPHERY

• Lymph obstruction- due to surgery
• LV failure: increases the capillary venous pressure
• hypoprotenemia: water does not flow back in
• increased capillary permeability: more water is lost

Question 5

How a clot forms

Answer 5

Platelet plug:

• damage to endothelium- tissue factor released
• vasoconstriction
• restricted blood flow
• platelets adhere

Complement cascade:

• tissue factor causes prothrombin to become thrombin
• fibrinogen is converted to fibrin by thrombin
• forms mesh around clot

Question 6

Anti-clotting mechanisms:

Answer 6

• tissue factor pathway inhibitor-inhibits thrombin
• thrombomodulin-inhibits thrombin
• heparin-inhibits thrombin
• stop blood from contacting platelets
• prostacyclin and NO release- prevents platelet aggregation
• tissue plasminogen activator- digests clots