Microcirculation Flashcards
In microcirculation, substances are transferred between??? How?
Between plasma and interstitial fluid by diffusion
What can diffuse directly through cell membrane of capillaries?
Lipid soluble substances (CO2, O2)
How does water soluble substances cross capillary walls? Give examples
Water-filled intercellular clefts (pores). H20, sodium, chloride.
Describe width of capillary intercellular slit pores in a typical muscle capillary.
VERY SMALL
Permeability of capillary pores for different substances varies according…
According to their molecular diameters
T/F Capillaries in different tissues have similar permeabilities.
FALSE.
There are extreme differences. Brain has tight junctions with pores very close together (blood brain barrier) to prevent substances from getting into brain. Liver has large gaps/pores because liver metabolizes a lot of substances.
Factors for diffusion
1-concentration gradient
2-Size of molecule
3-Size of pore
Kidneys have how many microcirculation systems
2
General net fluid movement across capillaries
1-Absorb at arterial end
2-Reabsorb at venous end (but not everything is absorbed)
3-Whatever is not absorbed, lymphatics pick up.
Edema occurs if there is low reabsorbtion and lymphatic don’t pick up.
What are the primary forces that determine fluid movement through capillary membrane. All move fluid in what direction?
- Capillary pressure
- Plasma colloid osmotic pressure
- Interstitial fluid pressure
- Interstitial fluid colloid osmotic pressure
Move in ONE direction
Explain capillary hydrostatic pressure
Pushes fluid OUT of capillary pores “holes in hose”
Pushes water into interstitial fluid
Explain interstitial fluid hydrostatic pressure
Can have (-) or (+) pressure
+)Pushing fluid INTO capillary
(-)Vacuuming fluid OUT of capillary (most cases is (-)
Explain colloid osmotic pressure
Proteins in plasma in capillaries oppose filtration to keep water in capillaries.
Opposes filtration causing osmosis of water inward through the membrane.
Explain Interstitial fluid colloid osmotic pressure
Proteins in plasma in interstitiual fluid try to PULL H20 out of caps.
Capillary filtration coefficien (Kf) measures. Describe using kidney, liver, and brain.
Measure of the capacity of the capillary membrane to filter water given net filtration pressure.
Capillary bed with more/or wider pumps have higher Kf
So, Liver Kf >Brain Kf
Kidney Kf> Brain Kf
Explain hydrostatic pressure from arterial end to venous end
As blood goes from arterial end to venous end the hydrostatic pressure decreases.
So arterial side, water trying to be pushed out of capillary
Venous side, water trying to be pushed into capillary.
What causes the majority of colloid osmotic pressure of plasma?
Albumin (75%)
Globulins (25%)
Interstitial fluid colloid osmotic pressure
Small amounts of proteins leak through capillary membranes into interstitial space based on pores in tissue.
The more protein the higher osmotic pressure.
Excess fluid that is not reabsorbed into venous end of capillaries goes…
Into lymph vessels and dumped back into circulation via subclavian vein.
What happens if lymph vessels are blocked?
You’ll get fluid build up-edema
Explain what would happen in microcirculation with a dog that had heart worms
Due to increase in atrial pressure, there’s an increase in venous pressure. There is an increase in filtration of capillaries (interstitial fluid coming out of capillaries) at atrial end and not much absorbing of interstitial fluid at venous end.
If lymphatic system doesn’t drain excess interstitual fluid, and there’s heart failure on the right side, edema forms in peripheral system (legs, abdomen, etc)
If lymphatic system doesn’t drain excess interstitual fluid, and there’s heart failure on the left side, edema forms in pulmonary system (llungs).
Benefits of lymphatic system
- Prevents edema
- Returns proteins and high molecular weight substances that can’t be reabsorbed into blood
- Major route for absorption of nutrients from the GI tract
- Plays important role in the immune system- picks up bacteria.
Factors that increase interstitial fluid pressure and lymph flow
- elevated capillary pressure
- decreased plasma colloid osmotic pressure
- Increased interstitial fluid colloid osmotic pressure
- Increased permeability of capillaries
Three scenarios where capillary pressure is increased or plasma colloid interstitial fluid pressure is increased
1-Nephrotic syndrome= decrease in plasma proteins
