Exchange and the Lymphatic System Flashcards
How are capillaries suited to diffusion?
- Lots of them so a lot of exchange can go on
- Very small and a large surface area to volume ratio so diffusion increases
What are the two bypass structures in a cap bed?
- Arteriovenous bypass
- Metarterioles
What is the distance between two epithelial cells known as?
Cleft
Which capillaries have large pores?
Fenestrated capillaries
Describe continous capillaries
- Leaky celfts between cells
- No channels
Where would you find specialised continuous capillaries that have no clefts of channels?
- Blood brain barrier
- Blood testes/ovary barrier
Where would you find specialised continuous capillaries that have larger clefts?
Muscle
Where would you find fenestrated capillaries?
Intestine
What are discontinuous capillaries?
Have massive channels and clefts
Where would you find discontinuous capillaries?
Liver
Why are the capillaries in the liver discontinuous?
To allow lots of proteins to enter the bloodstream
What two aspects does clotting involve?
- Formation of a platelet plug
- Formation of a fibrin clot
What is the basement membrane that the capillary sits on made of?
- Collagen
What happens for a clot to begin to form?
Endothelium ruptures
What is the process of a blood clot forming after the endothelium ruptures?
- Collagen that is revealed attracts platelets
- This forms a platelet plug
- Fibrinogen floating in the blood is converted to fibrin by thrombin
- Fibrin plug created
When is the clotting mechanism dangerous?
If it occurs in capillaries where the blood flow is slow and has a higher chance of clotting
What 6 methods does the epithelium use to stop blood clotting from happening?
- Stops blood contacting collagen
- Produces prostacyclin and nitric oxide
- Produces tissue factor pathway inhibitor (TFPI)
- Expresses thrombomodulin
- Expresses heparin
- Secretes tissue plasminogen activator (t-PA)
How does stopping the blood contacting the collagen stop clotting?
No platelet aggregation
How does prostacyclin and NO stop clotting?
Both inhibit platelet aggregation
What does tissue factor pathway inhibitor (TFPI) stop the production of?
Thrombin
What does thrombomodulin do to stop clotting?
Binds to thrombin deactivating it
What does heparin act on to stop clotting?
Also inactivates thrombin in the same way as thrombomodulin
What does tissue plasminogen factor do?
- Converts plasminogen to plasmin
- Plasmin digests clot
What is self regulation in reference to diffusion?
- If cells use more oxygen the conc. gradient increases so more of it diffuses into the cell
What is non saturable in reference to diffusion?
- If oxygen required channel they’d have a maximum rate where they all become saturated
- Diffusion stops this
How do polar substances get through the capillary?
Through clefts/channels
What channels exist in the brain capillaries to allow glucose to cross the blood-brain barrier?
Glucose transporters
What is hydrostatic pressure?
- Think of a hose with holes in it
- As water moves through it some of it moves out
- The higher the pressure in the hose the more that will move out
What is osmotic pressure?
- Created by plasma proteins unable to leave capillaries
- Osmotic pressure draws water into the capillary
What is the osmotic pressure created by plasma proteins called?
Oncotic pressure
On average how much water is lost through hydrostatic pressure each day?
20L
On average how much water is regained through oncotic pressure each day?
17L
What happens to the remaining 3L that is lost?
Taken up by the lymphatic system
How does the fluid that enters the lymph vessels stay there?
Enters through 1 way valves
How is lymph able to move through the system back to the blood?
- Squeezed by smooth muscles contracting
- Eventually enters thoracic duct/right lymphatic duct
- Passes through lymph nodes on the way
In what ways can oedema come about?
- Lymph obstruction
- Raised central venous pressure
- Hypoproteinemia
- Increased capillary permeability
What can lymphatic obstruction be a result from?
- Filariasis (similar to elephantisis)
- Surgery
- Elephantisis (parasitic worms grow and multiply in lymph)
What can result in a raised central venous pressure?
Ventricular failure
How can a raised central venous pressure result in oedema?
Increases hydrostatic pressure
What can hypoproteinamia be due to?
- Nephrosis
- Liver failure
- Nutrition
Name a condition caused by hypoproteinemia
- Kwashiorkor
- Reduces oncotic gradient
