Exchange and the lymphatic system

Question 1

Describe the structure and function of capillaries

Answer 1

Structure: 1 cell thick means small thin wall for diffusion. small diameter and many means large surface area to volume ratio
Function: exchange in all parts pf tissues.

Question 2

List the three types of capillary

Answer 2

Continuous
Fenestrated
Discontinuous

Question 3

What is the function of clefts and channels in capillaries?

When they are temporary what are they formed by?

Answer 3

Go right through basement membrane and can go right through cells.
When temporary, formed by invagination of cell membrane

Question 4

Describe the structure of continuous capillaries and give an example

Answer 4

Clefts ONLY BETWEEN CELLS for small cells or no clefts.
Anything lipophilic is unable to get in.
Eg blood brain barrier

Question 5

Describe the structure of fenestrated capillaries and give an example

Answer 5

Clefts and channels in cells
Where a lot of exchange occurs
Eg small intestine

Question 6

Describe the structure of discontinuous capillaries and give an example

Answer 6

Clefts and massive channels

Eg liver

Question 7

Describe how clots are normally formed when an endothelium becomes damaged

Answer 7

Damage -> 
leakage of platelets out -> 
collagen in basement membrane and aggregate -> 
signals to thrombin -> 
activates fibrinogen -> 
converted to fibrin -> 
forms clot

Question 8

Describe the anti-clotting properties of the capillary endothelium

Answer 8

• Prevents platelets contacting collagen
• NO and prostacyclin prevent platelet aggregation
• INHIBITOR TISSUE PATHWAY FACTOR INHIBITOR, inhibiting part o the thrombin pathway
• THROMBOMODULIN expression inactivates thrombin
• Secretion of TISSUE PLASMINOGEN FACTOR activates PLASMINOGEN -> PLASMIN to lyse clot

Question 9

Name the three types of exchange that take place across capillary endothelium

Answer 9

Diffusion
Carrier-mediated transport
Bulk Flow

Question 10

Describe diffusion

Answer 10

Self regulation - increased concentration gradient -> increased supply (eg the more O2 used, the more supplied)
Non-saturable
Non-polar
Polar molecules - via clefts and channels

Question 11

Give an example of carrier-mediated transport

Answer 11

Glucose transporter at the blood brain barrier

Question 12

Describe bulk flow by defining hydrostatic and oncotic pressures

Answer 12

Hydrostatic pressure: higher pressure in plasma than interstitial fluid (ISF). This pushes water out of the capillaries leaving behind bigger solute molecules.
The bigger molecules create osmotic/oncotic pressures which lead to water re-entering the capillary

Question 13

State the equation for net filtration pressure

Answer 13

Net filtration pressure = (Pc-Pif) - (Pi p - Pi if)

Question 14

Of the 20l of fluid that leaves the capilliaries each day, how much is regained?

Answer 14

17l

Question 15

What happens to the 3l from capillaries that isn’t reabsorbed back into the capillaries

Answer 15

3l in interstitial fluid -> 
lymphatic capillaries -> 
lymphatic vessels -> 
lymph nodes -> 
venous blood (via thoracic or right lymphatic (RUQ only) duct)

Question 16

Define oedema

Answer 16

Excessive fluid accumulation

Question 17

List the causes of oedema and give examples

Answer 17

Lymphatic obstruction eg filiarisis, surgery
Raised CVP eg RV failure
Hyperproteinaemia eg nephrosis, liver failure, malnutrition (kwashiorkor)
Increased capillary permeability eg inflammation - rheumatism