Exchange and Lymphatic System Flashcards
What is the space called between two cells?
Cleft - varies in size depending on how close cells are together
Describe the pore size in fenestrated capillaries
Large (fenestrations or pores)
Allows direct travel through the cell
Where do you find continuous capillaries?
brain
no clefts or channels in capillaries
Give an example of what the blood brain barrier might halt the diffusion of?
Potassium
Where might you find fenestrated capillaries?
intestine - contains clefts and channels
Where might you find discontinuous capillaries?
Liver - Lots of proteins made and need to enter plasma - leave via sinusoids
Contains clefts and massive channels
What part of a blood vessel is very involved in the formation of blood clots?
Endothelium
What are the two stages clot formation?
Formation of a platelet plug
Formatin of a fibrin clot
When will platelets start releasing clotting factor?
When integrity of endothelium is compromised and platelets have access to collagen of basement membrane
What is the function of thrombin?
Converts fibrinogen to fibrin
How does the epithelium prevent clot formation?
Stops blood contacting collagen
Produces prostacyclin and NO
Produces tissue factor pathway inhibitor (TFPI)
Expresses thrombomodulin (anticoagulant)
Expresses heparin
Secretes tissue plasminogen activator
What is the effect of stopping blood contacting collagen?
No platelet aggregation
What is the effect of prostacyclin and NO?
Both inhibit platelet aggregation
What is the effect of tissue factor pathway inhibitor?
Stops thrombin production
What is the effect of thrombomodulin?
Binds thrombin and inactivates it
What is the effect of heparin?
Also inactivates thrombin
What is the effect of tissue plasminogen activator?
Turns plasminogen into plasmin which digests clot
Why is diffusion described as self-regulating?
More O2 needed means more O2 enters the cell by means of diffusion
Why is diffusion of O2 described as unsaturable?
no use of protein pumps (no chance of all pumps being used at once)
Why type of substances can cross membranes?
Non-polar substances
What type of substances travel through clefts and channels?
Polar substances (potassium, glucose)
What type of molecules are carrier mediated transport?
Glucose transporter in brain
What are the pressures responsible for the green and black arrows?
Green - hydrostatic pressure
Black - oncotic pressure
Why does water get drawn back into the capillary?
Concentration of proteins increases from left to right (creates osmotic pressure) draws water back in
What is the average volumes of water which are lost and regained each day?
Lost - 20L
Regained - 17L
What causes Kwashiorkor?
Hypoproteinaemia
no production of osmotic pressure and little water renters the capillary.
What is oedema defined as?
Accumulation of excess fluid
What are the causes of oedema?
Lymphatic obstruction (eg to filariasis surgery)
Raised central venous pressure - due to ventricular failure - increase in hydrostatic pressure
Hypoproteinaemia - water leaves capillaries by hydrostatic pressure, re-enters via oncotic pressure - absent here Causes - nephrosis, liver failure
Increased capillary permeability - inflammation eg. rheumatism
Why does heart failure result in oedema?
Backward failure of right ventricle leads to congestion of systemic capillaries
This generates excess fluid accumulation body
Increased pressure forces additional fluid out of blood into tissue
This results in oedema in tissue
Right sided heart failure commonly starts in ankles where venous pressure is high due to effects of gravity
Might occur in abdominal cavity where fluid build-up is called ascites
