10. Exchange and the Lymphatic System Flashcards
What allows arterioles to constrict and dilate for good blood regulation and control?
- smooth muscle around it (layers of endothelial cells)
What allows capillaries to have an effective gas exchange mechanism? (2)
- short distance for diffusion due to one cell thick wall
- high SA:volume ratio
Do capillaries have smooth muscle around them?
No, just one cell-thick walls
What gross structure features of capillaries makes them ideal for exchange?
- lots in numbers
- thin walled (small diffusion barrier)
- small diameter ( big SA; volume)
What are 3 main types of capillaries?
- fenestrated
- continous
- discontinous
What determines capillary permeability?
Junctions between cells and the holes between them (either cells closely stuck together or slightly separated)
What is the structure of continous capillaries?
- no clefts or channels
Where do continous capillaries exist in the body?
in the brain (blood-brain barrier prevents K leaking out acrs)
What is an exception of continous capillaries where clefts exist? (in which body region?)
in muscles
What is the structure of fenestrated capillaries?
clefts and channels
Where do fenestrated capillaries exist in the body?
in the intestine
What is the structure of discontinous capillaries?
clefts and massive channels
Where do discontinous capillaries exist in the body?
in the liver
Do majority of capillaries have clefts?
Yes
What 2 things does clotting involve?
- formation of a platelet plug
2. formation of a fibrin clot
What enzyme converts fibrinogen to fibrin for forming clots?
thrombin
Describe the mechanism for forming clots.
- platelets react with collagen and clump together
- this forms a platelet plug
- fibrin clot (made from fibrinogen) then attaches to the platelet plug forming the clot.
What are anti-clotting mechanisms of the endothelium?
- 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 contacting collagen prevent clotting?
endothelium forms a physical barrier between platelets interacting collagen and no platelet aggregation happens
How does production of prostacyclin and NO prevent clots?
both inhibit platelet aggregation
How does production of tissue factor pathway inhibitor (TFPU) prevent clots?
it stops thrombin production
How does expression of thrombomodulin prevent clots?
it binds thrombin and inactivates it
How does expression of hepatin prevent clots?
inactivates thrombin
How does secretion of tissue plasminogen activator (t-PA) prevent clots?
Does the opposite of thrombin (which forms clots), instead it BREAKS down and digests clots forming plasmin and digested clot
What are 2 main features of diffusion?
- self-regulating
2. non-saturable (the more O2 available, the more O2 will travel across, it’s not limited)
How do non-polar and polar substances travel across membranes?
- non-polar substances diffuse straight across membrane
- polar substances diffuse through clefts and channels
In what 2 ways does exchange in capillaries happen?
- diffusion
2. carrier-mediated transport/facilitated diffusion (e.g. glucose transporter) which doesn’t use energy
Which blood vessels have the highest and lowest pressures?
- arterioles have highest hydrostatic pressure
- venules have lowest hydrostatic pressure
What pressure pushes fluid and solute OUT of the capillaries?
Hydrostatic pressure (increases filtration
What pressure pulls fluid into the capillaries and/ or prevents fluid from leaving?
Osmotic (oncotic) pressure
Roughly how much fluid in litres is lost each day?
~20L
Roughly how much fluid in litres is regained each day?
~17L
Why does concentration of proteins go up as you move along a capillary?
Because water continually leaks out of capillary (like a hose) whereas proteins are too big to get through and leak out so conc. increases as you move along the capillary tube
What happens to remaining 3L of fluid in capillaries?
gets “recycled” and re-used in the lymphatic system
What are 2 parts of Starling’s forces?
- capillary hydrostatic pressure via ISF hydrostatic pressure (first part in equation)
- plasma osmotic pressure vs ISF osmotic pressure (second part in equation)
What is the general equation for net filtration pressure?
(Hydrostatic forces of capillary-ISF) - (plasma osmotic pressure -ISF osmotic pressure)
How does lymphatic system regulate body fluids?
- fluid is pushed into intracellular space by hydrostatic pressures
- this interstitial fluid is reabsorbed into lymph capillaries and becomes lymph
- lymph squeezed fluid into lymph nodes are return it into venous system eventually
What can occur if too much interstitial fluid leaks out of capillaries?
oedema
Do lymphatic vessels have valves?
Yes
What is the definition of oedema?
accumulation of excess fluid
What are the 4 causes of oedema?
- lympathic obstruction
- raised ventral venous pressure (CVP)
- hypoproteinemia
- increased capillary permeability
What can cause a lymphatic obstruction? (2)
- surgery
- filariasis
What can cause raised central venous pressure?
ventricular failure (blood is pumped out and more is accumulating from the venous side on the right side, which means hydrostatic pressures are not in balance)
What can cause hypoproteinemia? (3)
- nephrosis (losing protein in kidney due to abnormal function)
- liver failure
- nutrition
What can cause increased capillary permeability?
- inflammation (e.g. rheumatism)
Which organ is the only place where specific carriers are needed for diffusion purposes?
the brain
