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
nodes in the lymph system
prevent pathogens from getting dumped into the circulatory system
increase of 20 mmHG in SBP and 10 mmHG DBOM
2x increase risk of death from
stroke
heart dz
other vascular dz
these structures transport blood under high pressures to the tissues and have strong vascular walls and rapid flow
arteries
these are the last small branches of the arterial system and act as control conduits through which blood is released into the capillaries
the arterioles
this is the site of fluid exchange nutrients and other substances in the blood and the interstitial fluid
capillaries
these structures collect blood from the capillaries
venules
these structures function as conduits to transport blood from the tissues back to the heart
veins
compared to the arteries, veins have ____walls and ____ pressure
thin walls and low pressure
arteriel pressure is controlled by what
independent of CO or local flow but rather nervous reflexes that increase HR
contraction of venous reservoirs (more blood to the heart) and constriction of most of the arterioles throughout the body
also the kidenys play a role via hormones
what is the equation for determining blood flow through a vessel
Flow= change in pressure over resistance
the percentage of blood that is composed of cells is called the ______ and is usually around _____
hematorcit
40
which is to say that 40 % of the blood is cells
___________ attenuates the effect of aterial pressure on tissues
autoregualation
through changes in vascular resistance
the two most important factors that can influence pulse pressure
1) increased stroke volume
2) decreased arterial compliance usually due to arteriosclerosis
what changes in pulse pressure would we see with a patent ductus arteriosus
some of the blood pumped through the aorta flows immediately through the patent ducuts into the pulmonary artery causing the diastolic pressure to be very low
which means a very great pulse pressure would be observed and
what changes in pulse pressure would we see with a aortic valve stenosis
you would see a diminished pulse pressure because of the inability of blood to make it through the valve
what changes in pulse pressure would we see with aortic regurgitation
aortic pressure would fall very low because of back flow leading to an increase in pulse pressure
kortkoff sounds
sounds heard with auscultation when the bp cuff is sufficient to close an artery during part of the cycle
when the blood pressure cuff falls below the systolic pressure you can hear a sound
