Capillary Permeability Week 5 test 2 Flashcards
Cell type of capillary wall
single layer of endothelial cells to promote efficient exchange
capillary exchange
all nutrients, gases, metabolites and water are continuously exchanged between the blood and cells
What are the two reasons capillaries are efficient sites for gas and nutrient exchange?
- blood velocity is low give adequate time to allow exchange across the membrane
- capillaries have a HUGE surface area for gas and nutrient exchange.
Stats on capillaries
more than 10 million capillaries, equivalent to about 25,000 miles of capillaries
Diffusion
movement of nutrients, gas and lipid soluble substances through the semipermeable capillary wall.
**plasma proteins generally cannot cross the capillary wall
Bulk Flow (ultrofiltration)
movement of protein free ECF and water soluble substances in and out through water filled pores or intercellular clefts
Vesicular transport
translocation of larger, exchangeable macromolecules across capillary endothelium via vesicular trancytosis (pinocytosis, calveolae)
4 factors that affect the rate of diffusion
- faster at higher temps
- faster with higher concentration gradient
- faster for smaller solutes
- slower in more viscous solutions
* * diffusion can only occur if membrane is permeable to the solute
difference between water soluble materials and fat soluble materials
water soluble materials must pass through fenestrations
eg. ions, glucose , AAs
lipid soluble can pass directly through plasma mem.
eg. gases, steroid hormones
hydrostatic pressure and oncotic pressure operate at capillary beds to cause most of the plasmas fluid to be filtered and reabsorbed where?
filtration occurs at arteriolar end 20L/Day
reabsorption occurs at venous end 17 L/Day
where does the fluid in the interstitial space go that isn’t reabsorbed in the venous side of the capillary?
lymphatic vessels collect excess interstitial fluid and return it to the venous bloodstream.
once in the lymphatic vessels it is called lymph
Crystalline osmotic pressure
oncotic pressure due to small molecules in the plasma(mainly NaCl, Na HCO3, glucose, urea, AAs).
-since these are all water soluble their concentrations are equivalent on either side of capillary wall so there is NO EFFECT on water flow!!
Oncotic pressure aka colloid osmotic pressure
osmotic pressure exerted by impermeable plasma proteins, notably albumin, in blood vessels plasma that pull water into the circulatory system from the interstitial fluid.
increases along the length of the capillary due to the proteins concentrating because they don’t filter
hydrostatic pressure
force that is directed out of the capillary by a fluid pushing against the capillary wall.
what two pressures are responsible for capillary transfers?
hydrostatic and oncotic
Net filtration pressure
net forces pushing out - net forces pushing in
(capillary hydrostatic pressure + osmotic pressure due to interstitial fluid protein concentration) (-) (interstitial hydrostatic pressure+ oncotic pressure due to protein concentration.)
Forces at the arteriolar end
hydrostatic out and osmotic in, net is out
postive value
forces at the venous end
hydrostatic is out and osmotic is in, this time net is in because the osmotic pressure is higher
-negative value
hydrostatic pressure
largest pressure drop is from arteries to arterioles
SM in arterioles tightly regulate BP in capillaries
pressure progressively gets lower as blood leaves capillaries to the vena cava
capillary bed
branch off the metarteriole and return to the thoroughfare channel at the distal end of the bed; site of optimal exchange
vascular shunts
metarteriole-thoroughfare channel connecting an arteriole directly with a postcapillary venule (bypassing true capillary bed)
Precapillary sphincter
cuff of SM that surrounds each true capillary and regulates blood flow into the capillary in response to vasomotor nerves (sympathetic) and local chemical conditions, so it can either bypass or flood the capillary bed
Vesicular transport
translocation of large macromolecules in a membranous sac across capillary endothelium.
eg. fluids, large solutes, Abs
**requires ATP
Vesicles can also fuse together creating pores across endothelial cells for bulk flow transport.
Pinocytosis or Trancytosis
used both for endocytosis and for exocytosis
pinocytic vesicles formed at one surface of the cell may, after being detached, move through the cell to the opposite surface and there discharge their contents
Lymphatic capillaries
blind-ended sacs in interstitial space low pressure absorb fluids from interstitial space unidirectional wider than blood capillaries colorless and contain lymph
Potential causes of edema
increased capillary BP
decreased plasma colloid osmotic pressure
increased capillary permeability
obstruction/disruption of lymphatics
