AN SC 310
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What are the exchange mechanisms across capillary walls
- Diffusion (lipophobic and lipophillic)
- Transcytosis - exchangable proteins
- mediated transport - in brain
What is bulk flow? Filtration? absorption?
- Movement of solutes and water with the purpose to distrubute the ECF
- Filt = movement out of the capillary
- Abs = movement into the capillary
Force of bulk flow?
- Hydrostatic pressure gradient = force due to fluid
- osmotic pressure = osmotic pressure on water by non permeating solutes (proteins)
- oncotic pressure = osmotic pressure of proteins
Capilary hydrostatic pressure?
Interstial hydrostatic pressure?
- arteriole end = 38 mm Hg
- venous end = 16 mm Hg
- favours filtration
- 0-1 mm Hg
- favours reabsorption
Hydrostatic pressure gradient?
- Art: 38-1 = 37 mm Hg, filtration
- Ven: 16-1 = 15 mm Hg favours reaborption
Osmotic pressure gradient:
- Capillary oncotic osmotic pressure: 25 mm Hg favours reabsorption
- Interstital fluid oncotic osmotic pressure: 0-1 mm Hg favours filtration
25-0 = 25 mm Hg which favours reabsorption
Net Filtration pressure?
- Arteriole end: (38+0) - (25+1) = 12 mm Hg filtration
- Venous end: (16+0) - (25+1) = -10 mm Hg absorption
What is the effects of Net filtration pressure?
- Net acrosss capilary Filtration > Absorption
- 3 L per day of filtation
- lyphatic system will pick up all that is left and return to circulation
Factors effecting filtration/absorption
- standing on feet increases hydrostatic pressure
- injuries - capillaries damaged and leak fluid and proteins
- histamine increases and capillary permeability to proteins
- Liver disease
- Kidney disease
- Heart Disease
- smaller than arterioles
- connect capillaries to veins
- little smooth mushc in walls
- some exchange of material between blood and IF
- Large diameter
- valves allow unidirection of blood flow
Where are valves found in viens
in perpherial veins absent from central veins
How are veins a volume resovoir?
- Expand with little change in pressure
- 60% of total blood in systemic is present in them at rest
- veins hold a large volume with small pressure change due to high compliance
Skeletal muscle pump. What happens when it conracts and relaxes?
- Contract: squeezes on veins increasing pressure, blood moves to the heart cannot move back because of the veins
- relaxes: blood flows into the veins between muscles
Respiratory pump? Inspiration?
- Inspiration causes a decrease in pressure in thoracic cavity which causes an increase in the pressure in the adominal cavity
- pressure in the veins in the abdominal cavity creates gradient that favors blood movement to thoaric cavity
What happens with increased and decresed blood volume respect to venous pressure?
- increased leads to increased venous pressure
- decreased blood volume leads to decreased venous pressure
Venomotor tone? what causes an increase?
- Venomotor tone = smooth muscle tension in veins
- increase in venomotor tone is caused by contraction of smooth muscle in wall of vein. Leads to increase venous pressure and decreased venous compliance. Leads to increased stroke volume and increased cardiac output
- system of vessles, nodes and organs
- vessels that circulate excess filtrate
- lymphatic veins drain into thoracic duct which empties into right atrium
- contain macrophages
- filter lymph flowing thru the node. They are able to filter bacteria, toxins, or other foreign material
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