microcirculation Flashcards
controls flow into and out of capillary bed
i. Arteriole -
as vessel size goes down pressure
also goes down
what’s important to pressure is the total cross section diameter of the vascular system
aorta is the biggest artery in the body but there is only one of them
If you add up the total diameter of the capillaries in the system, the diameter of the system is way bigger than the diameter of the one single aorta
Coming off the arteriole there are small muscular rings called
precapillary sphincters
these dictate flow into the capillary bed
based on the needs of that organ
i. Vasomotion
contraction or relaxation of the small arterioles and the precapillary sphincters and the result of that is intermittent flow
b. Vasomotion regulation
Oxygen content/tension - tissues that are O2 starved will be dilated and will have more flow
nutrient demand theory
why does lipid or water soluble have to do with it?
Lipid soluble substance able to move through the membranes (CO2 can do this as well)
in order to move water soluble molecule you need a pore or transport molecule
what determines how a molecule might move across a capillary membrane
concentration: driving force
molecular size
solubility
presence or absence or a transport protein or channel that allows them to flow
what is interstitial fluid
Fluid like plasma with no proteins
i. Collagen fibers
ii. Polyuronic acid
iii. Glycose amino glycan
iv. These form the brush border and make the interstitial gelatinous
Only 1% free fluid
this is what get’s filtered out of the blood stream and proteins are big and negatively charged
Blood entering on the left from the arterial side, leaving on the right to enter the venous return back to the heart what will come out
Water, glucose w/ transport molecule , CO2 moving in and out of the bloodstream and into the tissue
this is going to happen at the front of the capillary and movement will be determined by STARLING FORCES
Balance of ______ is going to determine whether it has net filtration or absorption at this capillary bed
- Balance of starling forces is going to determine whether it has net filtration or absorption at this capillary bed
most important starling force
hydrostatic pressure
- Causes outward pressure
- Tend to filter fluid out and increase pressure in the vessel
Interstitial fluid pressure (Pif) is going to oppose
the capillary fluid pressure
when would you have high interstitial pressure
with edema
Plasma colloid pressure (IIp) comes from
non diffusible elements in the blood
cells
proteins
pressure from nondiffusable elements in the plasma that would tend to _____
pressure from nondiffusable elements in the plasma that would tend to draw the fluid in (inward pressure)
Donnan equilibrium effect
Pressure is a little bit higher than you would expect b/c proteins are negatively charged which attracts Ca++ ions around it and that makes the Ca++ attached to the proteins nondiffusable and enhances the amount of nondiffusable elements in the plasma
halo of Ca
donna with a halo
the theory is that the Ca is being sequestered in the blood because it is attracted to proteins
for this reason we see less movement of Ca
Interstitial fluid colloid osmotic pressure (IIif) . tends to
ii. Tend to pull fluid out of the vessel (outward pressure)
describe starling forces in the capillary
two fluid pressures oppose
two colloid pressures oppose
this balance determined filtration of absorption
why do we see negative interstitial fluid pressure
because the lymphatics are constantly pulling fluid back
Average capillary filtration pressure
~ 0.3 mmHg
1. Over our entire circulatory system, there is a small amount of fluid that does not get absorbed–> get it back through the lymphatic system
XIII. Starling Equilibrium - what is this
balancing of filtration and absorption
a. Fluid volume leaving capillaries is balanced by absorption at other capillaries and by lymphatic return
Normal net filtration about
b. Normal net filtration about 2ml/min
how does ascites and edema work?
i. The more pressure goes up, the more we filter, the bigger the demand on the lymphatic system to return that volume and the greater risk of ascites and edema when we overwhelm the lymphatic system’s ability to return that volume
lymphatic channels are characterized by there __ directional flow
i. There are valves to ensure one way flow
ii. No pumps
iii. Open ended tubes to collect the lymph
