Exchange and the Lymphatic System Flashcards
In what 3 ways are capillaries specialised for exchange?
- There are lots of them with every tissue being within 100 micrometres of one
- Thin-walled presenting a small diffusion barrier
- Small diameter producing a big surface area to volume ratio
What do continuous capillaries contain?
Cell junctions which are tight together
What do fenestrated capillaries contain?
Clefts and channels
What are absent in the continuous capillaries found in the brain?
Channels and clefts
What are found in the fenestrated capillaries?
Clefts and channels
Give an example of where fenestrated capillaries are found.
Intestine
What are found in the discontinuous capillaries?
Clefts and massive channels
Give an example of where discontinuous capillaries would be found?
Liver
Why are discontinuous capillaries found in the liver?
Exchange of proteins
What does clotting involve?
- Formation of a platelet plug
- Formation of a fibrin clot
How is a platelet plug formed?
- If the endothelium is torn then there is exposure to the basement membrane
- There is exposure to collagen which forms the platelet clot
How is a fibrin clot formed?
Thrombin acts on fibrinogen to form fibrin
What anti-clotting mechanisms of the endothelium are there?
- Stops blood contacting collagen
- Produces prostacyclin and NO
- Produces tissue factor pathway inhibitor (TFPI)
- Expresses thrombomodulin
- Expresses heparin
- Secretes tissue plasminogen activator (t-PA)
How does stopping blood contact with collagen prevent clotting?
Stops platelet aggregation
How does producing prostacyclin and NO prevent clotting?
Inhibits platelet aggregation
How does producing TFPI prevent clotting?
Stops thrombin production and inactivates it
How does expressing thrombomodulin prevent clotting?
Inactivates thrombin
How does the secretion of t-PA prevent clotting?
Plasminogen becomes plasmin and digests any clot formed
In what ways can molecules be exchanged between tissues and the capillaries?
- Diffusion
- Carrier-mediated transport
- Bulk flow
How does diffusion allow transport?
- Self regulates as it responds to concentration gradients
- Non-saturable as it responds to changes in the concentration gradient
- Non-polar substances diffuse across the membrane
- Polar substance diffuse through clefts and channels
Give an example of a carrier-mediated transporter.
Glucose transporter
What are the 2 pressures involved in Starlings forces?
- Capillary hydrostatic pressure vs ISF hydrostatic pressure
- Plasm osmotic pressure vs ISF osmotic pressure
How does the hydrostatic pressure vary from arteriole to venule?
Decreases
How does the osmotic pressure vary from arteriole to venule?
Increases
Which side of the capillary is the high pressure side?
Arteriole
How is bulk flow established?
- Hydrostatic pressure greater at arteriole
- Water is moved out of the capillary from arteriole to venule
- There is therefore an increase in the solutes concentration
- In response the osmotic pressure increases from arteriole to venule
What is the fluid exchange of bulk flow?
- 20l lost per day
- 17l gained per day
- 3l enters the lymphatic system
What is Kwashiorkor caused by?
Insufficient protein in the diet leading to proteinemia and causing an imbalance in starling forces
What do lymph capillaries tend towards?
The heart
What happens when skeletal muscle contracts?
Squeezes on lymph system
What is oedema?
Accumulation of fluid
What 4 states can cause oedema?
- Lymphatic obstruction
- Raised CVP
- Hypoproteinemia
- Increased capillary permeability
What can cause lymphatic obstruction?
- Filariasis
- Surgery
What can cause raised CVP?
Ventricular failure
What can cause hypoproteinemia?
- Nephrosis
- Liver failure
- Nutrition
What can cause increased capillary permeability?
-Inflammation e.g rheumatism
