Flashcards in Circulation 1: Hemodynamics Deck (61):
What is the function of ...
arterial side- control pressure
venous side- control volume
global control- sympathetic
local control- dep. on metabolic demand
Clinically the central venous pressure is used to monitor blood volume very carefully. Why?
If someone is bleeding internally would you see a change in arterial pressure or venous pressure?
bc its v sensitive to blood volume
see a change in venous pressure immediately and no change at all in arterial pressure. why? bc arterial pressure is regulated by baroreceptor reflex. and you need to lose a large volume of fluid before you start to see changes in arterial pressure. on other side of system, venous system not regulated at all. big bag of fluid. not strong regulation bc holds volume. arterial side maintains pressure. volume side-venous. has low pressure under normal conditions (between 2-5) and small changes in volume cause dramatic changes in pressure bc not regulated. thats what central venous line is for- measure pressure… give transfusion, is pressure going back up? bc that pressure pushes blood into heart.
What is a main job of the circulatory system?
maintain arterial bp.
that bp is designed to perfuse and bring O to tissues.
There is not enough blood in the circulatory system to perfuse all organs at the same moment. How does the circulatory system compensate?
circulatory system designed to distribute blood to organs that need blood at moment. little blood to GI unless eating. little blood to skeletal while sitting. blood to brain… most of blood to 3 vital organs (brain, pulmonary system and heart) , 25 percent to kidneys all the time… brain needs constant O. even 5 sec without it and you’d pass out. v dep. on O. as far as body those are only 3 that need to be perfused all the time
so during hypo-volumic shock. bleeding, the sympathetic baroreceptor reflex closes blood flow to kidneys, splanchin region, skin, and shunts blood to 3 vital organs.
What is Poiseuille's Law? Describe it and provide the equation.
Describes how blood flow is regulated
-applies to steady laminar flow of Newtonian fluids through uniform cylindrical tubes.
(CV system is composed of branching, elastic tubes of varying diameter and a non-Newtonian fluid (blood)
-analogous to Ohm's Law
Law: F= P/R (change in pressure over Resistance)
1. Flow is directly proportional to pressure gradient
2. Flow inversely proportional to resistance
F= (P1-P2) pi r^4/(8L x viscosity)
Blood flow is directly proportional to the pressure gradient.
Blood flow is directly proportional to the vessel radius to the fourth power.
Blood flow is inversely proportional to vessel length and blood viscosity.
Resistance is directly proportional to the vessel length and blood viscosity.
Resistance is inversely proportional to vessel radius to the fourth power.
The most important determinants of blood flow in the cardiovascular system are the pressure gradient and radius to the fourth power. The pressure gradients are generally held constant by feedback mechanisms (baroreceptors). Therefore, small changes in arteriolar radius can cause large changes in blood flow to a tissue or organ because flow and radius are related by the fourth power.
What is flow equal to?
flow equal to pressure generated across cardiovascular system.
flow L to R, generates pressure gradient- blood flowing forward.
related to pi r^4 ...r is the radius of the vessel
What is the significance of r^4?
means that blood flow is related to the 4th power of radius of vessel which means that very small decreases in radius cause very large decrease in blood flow.
if vessel diameter increases 2 times. blood flow goes up r^4… 2^4… 16. so blood flow goes up 16x for increased diameter of only 2x.
Describe resistance and the relationship between resistance and radius.
Resistance is inversely related to r^4. as radius goes up, resistance goes down by the same factor.
R= 8/viscosity x Lviscosity/r^4
Resistance is related to the L of the tube... as blood flows across circulatory system the tube is long, longer blood flows across tube the more resistance it encounters. one of reasons bp drops over distance
Describe how length of system is related to bp.
as blood flows across circulatory system the tube is long, longer blood flows across tube the more resistance it encounters. one of reasons bp drops over distance. L of system - resistance is high. as blood flows arterial side, capillaries to venous side, that L affects resistance of system or det. resistance of system. one reason bp drops, losing E against that resistance
What is viscosity?
viscosity directly related to resistance. higher viscosity, higher resistance. viscosity =(internal frictional resistance of fluid flowing across itself) …
=internal frictional resistance between adjacent layers of a fluid
Why does the L ventricle generate so much more pressure than the R side even though the CO is the same?
pressure generated by L ventricle high even tho CO same bc of resistance… same CO generated by R ventricle but pressure low bc resistance low
Describe shear stress and shear rate and its relationship to viscosity. How do they relate to each other (Provide equations for viscosity and shear rate)
shear stress= resistance to movement between laminae (pressure)
shear rate= relative velocities between laminae (velocity of blood flow)
viscosity= shear stress/shear rate (pressure/velocity of fluid thru system)
shear rate (V)= shear stress (P)/viscosity
Describe the parabolic profile of velocity.
If viscosity is very low how will that affect the parabolic profile?
In a blood vessel the shearing laminae of blood are concentric cylinders that move with different velocities. The inner most cylinder moves with the highest velocity, while the outermost cylinder moves at the slowest velocity. As a result, the velocity profile is a parabola with the maximum velocity at the central axis.
The lower the viscosity, the sharper the parabolic profile.
if blood flow moving faster bc of viscosity, would stick out every further bc internal axial flow even faster compared to flow against wall. lower viscosity means lower internal frictional resistance so velocity of flow faster
Describe the layers of laminar flow in a blood vessel.
velocity of blood flow not uniform throughout cross sectional area of tube. faster is axial flow (right in middle) layer 5. slowest is against the wall of vessel (Layer 0,1)… fluid right up against wall is at 0 velocity not moving at all. v thin. as you go more and more axially further from that resistance at wall, fluid flow increases and creates parabolic profile. this is referred to as laminar flow. in terms of viscosity - each diff concentric layers flowing across e/o bc flowing at diff velocities.
What would happen if all the layers went at the same velocity?
What if shear rate goes up? What causes it?
if same velocity there’d be no viscosity bc no frictional resistance except at wall. internal frictional resistance is diff concentric layers flowing across e/o.
look at eq. if shear rate goes up, no sig. change in pressure causing it then thats a decrease in viscosity. if shear rate goes up, velocity of flow increases but not bc of increase in pressure, shear stress constant then fraction goes down and thats decrease in viscosity. if shear rate goes down and pressure didnt change then viscosity has gone up.
What are the units of viscosity?
poise (dyne sec/cm2)
Describe Newtonian vs non-Newtonian fluids.
a) Newtonian fluid - a fluid whose viscosity remains constant over a range of shear rates and shear stress. Homogeneous fluid. Ex. water or plasma.
(if increase velocity of fluid flow, pressure goes up same as shear stress. shear rate goes up together. so fraction stays same. no change in viscosity if increase velocity of water flow. homogenous fluid. therefore viscosity doesn't change as flow rate changes)
b) non-Newtonian fluid - a fluid whose viscosity changes over a range of shear rates and shear stress. Non-homogenous fluid
Ex. whole blood (RBC, WBC, proteins).
(has components in it, main component in blood that makes it non-homogenous with plasma is RBC, proteins. as result they interact w each other and don't behave as newtonian fluid. as shear rate goes up, as velocity goes up, viscosity comes down by inherent interactions or lack of interactions between these molecules. bc of interactions of RBC proteins and WBC, as shear rate goes up (velocity of blood flow increases) viscosity comes down …blood flow slows down, more chances to interact w each other and viscosity goes up.)
As velocity of blood flow increases, viscosity decreases due to less interactions between components.
Discuss the effect of hematocrit on viscosity.
What would low or high hematocrit mean? Clinical ex.
Relative viscosity increases progressively as hematocrit increases. as hematocrit increases viscosity increases…not linear relationship. has dramatic effect at higher hematocrit. so can change viscosity of blood by changing number of RBC. interaction w diff components.
This effect can be significant.
a) anemia - low hematocrit - relatively low viscosity
b) polycythemia - high hematocrit - relatively high viscosity.
Increased erythropoietin (high altitude). Multiple myeloma.
What is the normal range of hematocrit?
What is blood doping?
take out couple units of blood, store, then go out and exercise at high altitude (increase RBC by acclimating to high altitude)… 2-3 months. takes months for RBC to regenerate… get normal content right. then right before compete put blood back into system and now you have a lot more RBC than before. increases O carrying capacity. more O to tissues. improves performance. increases viscosity… more difficult for heart to pump fluid around system… strong athlete the extra resistance wont make much diff. but if older person it could
Why might you hear the blood flow of someone with anemia?
low viscosity, velocity of blood flow changes in body and hear it as murmurs.
What is axial streaming? What are the implications for this?
tendency of RBC to accumulate in axial laminae at high shear rates
tendency of RBC to accumulate in axial lamina. what happens is blood vessel…laminar blood flow and parabolic function, center axial lamina fastest, as go into smaller vessels (less than 200 microns), RBC line up in the middle…thats axial streaming. RBC more confined to fastest lamina and now have situation where most periphery of vessel is plasma-rep. much lower internal resistance. this mechanism offsets what we just talked about- as blood flow slows, viscosity should go up. but because small diameter reduces viscosity, the net effect is that viscosity ins decreasing as gets into smaller and smaller vessels-easier for heart to push blood through smaller vessels.
Describe viscosity and velocity as blood travels through arterial system to capillaries to veins.
As blood travels down arterial system, reduce pressure on system and reduce velocity of blood flow in system. Blood slower and slower as goes to capillaries, means viscosity of blood going up. but as blood flows into smaller tubes, rel. viscosity comes down due to axial streaming.
normal decrease in blood flow, or decrease in blood velocity which would raise viscosity is offset by decrease in diameter of these vessels. and net effect is decrease in viscosity in peripheral vessels.
What is plasma skimming?
tendency of smaller vessels to contain relatively more plasma and less red blood cells due to axial streaming.
(As blood flow slows down from larger to smaller vessels, the viscosity should increase, but it doesn’t in small vessels (200 microns or less), because of axial streaming)
if small vessel branching into even smaller vessel- bc of axial streaming (RBC confided to axial lamina) less RBC go into smaller vessels and its more plasma… as tube diameter goes down, hematocrit goes down bc more plasma goes into smaller vessels
How does plasma skimming affect the hematocrit? Draw a graph comparing tube diameter to relative hematocrit ratio.
What would happen if you took a vena puncture from a large vein vs a finger puncture. When centrifuged what would you see?
hematocrit is lower is small vessels compared to larger vessels bc of plasma skimming.
what does mean clinically? if you take a vena puncture from large vein in someones arm and spin it down and look for hematocrit (percent of RBC in relation to total volume of blood..should be about 45 percent) … RBC pushed down so see white area at top. 45 percent of total. sep. plasma from RBC… if take finger puncture and puncture capillary or group of capillaries and took that blood and put in tube and spin it hematocrit about 40 percent, about 5 percent less bc of axial streaming and plasma skimming. bc of RBC confined to axial lamina, more plasma at periphery of vessel and therefore less RBC go off into smaller vessels. hematocrit of smaller vessel is less than hematocrit of larger vessel. so dep. where you take the blood from. still w/in normal range.
What is laminar flow? Turbulent flow? Provide 4 examples.
Laminar flow- fluid moves in parallel concentric layers within a tube. Laminar flow is silent
Turbulent flow: disorderly pattern of fluid movement; non-laminar
a) murmurs, bruits (if have stenosis and throw clot in carotid, no where else for blood to go, will squirt through and hear Brewie)
b) damage do endothelial lining
d) Korotkoff sounds (based on changes in the velocity of blood flow, production of turbulent flow)
What is Reynold's number? Discuss how it changes with higher velocity.
indicating propensity for turbulent blood flow; the
higher the Reynold's number (>3000), the greater
the chance for turbulent blood flow to develop.
The larger the diameter, the higher the chance to develop turbulent flow (e.g. Aorta)
higher velocity-more change you get turbulent blood flow. divide by viscosity. if have lower viscosity, then higher chance of turbulent blood flow- why can hear murmurs more pronounced if have them w pt with anemia
What will happen in long tube in regards to pressure and resistance?
resistance to blood flow along wall goes back to resistance shown in P. eq w L. L of tube, the longer tube the more internal resistance you have along tube. so longer system, the more pressure will decrease as result of internal resistance.
(resistance directly proportional to vessel length, flow inversely related to L, flow directly related to pressure gradient...)
What is a Korotkoff sound?
inflate cuff, create stenosis create higher velocity of blood flow through that stenosis creates turbulent flow and every time the heart ejected volume through that stenosis you hear click and thats a Korotkoff sound. not heart sound. artificial sound you make.
cut cross sectional area then increase velocity of fluid flowing out of hose. same in CV system. imp. w stenosis. create stenosis w bp cuff in large artery… (blood has no where else to go) that has to be forced through small opening and increases velocity of blood flow.
What happens if endothelial lining is damaged? What can cause this damage?
turbulent blood flow can cause damage to endothelial lining.
once endothelial lining damaged get inflammatory responses which cause blood clots that can break off or rupture and cause embolisms.
Discuss blood flow in a-fib, what could happen?
in an area like in a-fib- don't have blood flow through atria, have it circulating in atria, can cause platelet aggregation and thrombi.
Between a beaker of water and beaker of oil, which has higher velocity?
Neither, has to be moving, has to have flow in order to have viscosity- internal frictional resistance based on rate...
How are diameter, viscosity, and velocity related to Reynold's number?
diameter directly related. viscosity inversely related. velocity direction related
Which perimeter, when you are using a bp cuff, causes turbulent blood flow? Lower diameter or velocity?
if lower diameter then you reduce the chances of getting turbulent blood flow. (no turbulence through stenotic region) but does increase velocity and velocity is directly related to Reynold’s number and its the velocity that causes turbulence. by lowering diameter causing increase in velocity but not the diameter that causes the turbulence- its the velocity.
How is velocity of blood flow related to cross sectional area?
blood flow is inversely related to cross sectional area.
(does not apply to the normal circulatory system as it branches into smaller vessels)
Why is blood flow slow in capillaries if they are the smallest and velocity of flow increases as cross sectional area of tube gets smaller?
NO. blood flow slows as goes further and further from heart as goes into tubes, bc getting more and more vessels and total cross sectional area gets larger and larger and gets enormous when gets to capillary area. if total cross sectional area increases (a to b, artery to capillaries) then blood flow through capillaries (bc total cross sectional area) then blood flow slows down, thats what happens in CV system
What is Bernoulli Principle? If there was an abrupt decrease in vessel cross sectional area, what would occur. Discuss in regards to pressure.
Define potential and kinetic energy. Provide equation.
What happens to lateral pressure as velocity of blood flow increases?
applies to large vessels in series...
in a constant flow system, the total E (potential and kinetic) remains constant.. (constant flow system= when blood HAS to go through stenosis like a carotid, femoral, brachial a stenosis.. not where blood vessels are parallel and can go around).
Ex. - at an abrupt decrease in vessel cross sectional area (stenosis), potential energy (pressure) is converted into kinetic energy (flow). As a result, transmural (static) pressure decreases as the velocity of blood flow increases in a stenotic region.
Potential energy = transmural (lateral) pressure, static
Kinetic energy = velocity of blood flow
Total energy (E) = potential energy (P) + velocity of blood flow (ρv2/2)
When the velocity of blood flow increases, the lateral pressure decreases...in stenosis region total E hasn’t changed but bc kinetic E component so much larger that means potential E reduced. lateral/transmural pressure within stenotic reduced. velocity of blood flow through stenosis much larger. back to larger diameter flow slows back down. potential E and kinetic E. means when velocity of blood flow increases, then lateral pressure across system decreases.
Describe how Bernoulli's principle relates to an arterial stenosis in the heart.
in heart has to do with arterial stenosis- blood flow through stenosis has less pressure on side of stenosis which enhances ability of stenosis to collapse. makes it easier for stenosis to continue to be stenotic. creating negative pressure or reducing pressure holding vessel open and stenosis collapse more … aortic stenosis- blood flow through stenotic valve so fast that it causes negative pressure on coronary cusps and pulls blood out of coronaries causing ischemia.
Explain the chart on slide 12. Why is transmural pressure in P4 lower than P6? What results?
Transmural pressure within the stenotic region (B,P4) is lower than in the downstream segment (C, P6) due to the higher velocity of blood flow through the stenotic region. As a result, blood flow is moving from a lower pressure within the stenosis to a higher pressure downstream from the stenosis. This demonstrates that blood flow does not necessary move from a higher to lower pressure. It is more correct to understand that blood flows from a higher to a lower total energy.
Where is total energy greatest? Stenotic region or downward segment? (Slide 12) Why?
Where is this seen in the heart?
This demonstrates that blood flow does not necessary move from a higher to lower pressure. It is more correct to understand that blood flows from a higher to a lower total energy.
The total energy is made up of both the potential (pressure) energy and the kinetic (movement) energy components. Total energy is in fact greater in the stenotic region than in the downstream segment because the kinetic energy component in the stenotic region is significantly higher than in the downstream segment. This same effect occurs with blood flow from the LV into the aorta where the kinetic energy component forces blood to flow momentarily against its pressure gradient.
On slide 12, describe the total energy comparing P1, P3 and P5.
*Note in the diagram above that the total energy (P1, P3 and P5) remains constant. This is incorrect. Total energy should be continuously decreasing from A-B-C, it is set as equal for didactic purposes.
What is the Laplace relationship.
Describe how it applies to capillaries, arteriolar vasoconstriction, aneurysm, dilated hearts.
wall tension = pressure x radius/wall thickness
wall tension is the force pulling the vessel open
1) Capillaries - small radius = low wall tension; can withstand very large trans-mural pressures.
2) Arteriolar vasoconstriction – relatively large wall thickness/lumen diameter ratio = low wall tension; provides greater control of vessel diameter and blood flow.
3) Aneurysm - large radius = high wall tension; cannot withstand trans-mural pressures and therefore will eventually rupture.
4) Dilated hearts - large radius = high wall tension; more systolic work (higher oxygen consumption) to overcome higher wall tension. Afterload, high wall tension opposes shortening ( 6% shortening, compared to 25% in normal hearts).
Describe the wall tension of a dilated heart and what results.
where heart is abnormally large. heart not hypertrophy. physically larger bc of volume diameter. larger diameter impedes shortening. pulling apart. in order for heart to eject volume must shorten. impedes shortening=afterload. one of most serious forms of afterload. this dilated heart, wall tension prevents heart/opposes shortening and generates enormous amount of O consumption for heart. radius alone is higher systolic work (shortening), higher O consumption to overcome wall tension. normal heart shortens about 25 percent. dilated heart about 6 percent. what this does to SV… lots of O to try to overcome that wall tension.
Describe an aneuyrsm, its wall tension and how blood flows through it.
larger radius… wall damaged bulging out. higher wall tension at that point. that tends to stretch it out further. changes all 3 parameters. blood flow through aneurysm? (v of blood flow through wider part of tube)…slows down. lateral pressure generated if velocity of blood flow slows down according to B principal ? it increases and therefore pressure across vessel wall much greater. so pressure goes up at aneurysm bc of Bernellis. blood flow slows, lateral pressure increasing, kinetic E goes down, lateral pressure goes up. so pressure goes up, radius goes up, wall tension up, what happens to wall thickness when this stretches out? goes down, thins out, like stretching a balloon. E to enhance wall tension,pressure up, E up, thickness down- all increase wall tension. so matter of WHEN will rupture. positive rupture. can have in heart, arteries… the 2 abnormalities.
Why is it that if you jump off a high platform the capillaries in your feet don't rupture even though pressure may go up to 200-300mmHg?
capillaries v small radius, v low wall tension and can withstand v large transmural pressures as a result. so if you have capillaries in feet and jump off high platform pressure in capillaries goes up 200-300 mmHg but you don't rupture the capillaries. bc diameter of capillaries so small and wall tension so little that can withstand high pressure
Why is it that small arterioles can vasoconstrict and dilate easily? (What is their function)
(they distribute blood to individual tissues)
low wall tension (small radius and large wall thickness which is the vascular smooth muscle that surrounds them)
so that large wall thickness and small lumen diameter makes it easy for vascular smooth muscle to close and constrict vessels and reduce blood flow. i
Define resistances in series. What happens if you add a resistor?
Series: For resistances in series, the total resistance of the entire system equals the sum of the individual resistances. Therefore, each resistance is less than the entire system.
Ex. Aorta, large arteries, small arteries, arterioles, capillaries, venules, veins, vena cava.
Arterioles are the primary site of arterial resistance
functionally if increase resistance of any one of these resistors, these structures then it'll increase resistance throughout system
Describe why it is that arterioles are a primary site of arterial resistance.
arterioles have v strong smooth muscle vascular coat, allow diameter to be regulated carefully. wall thickness to lumen diameter ratio- these vessels along with pre-capillary sphincters have v thick wall of vascular smooth muscle, so reduces wall tension (Le Place relationship), and have v small diameters- less than 200 microns ..gives v small wall tension. wall tension is pulling tissue open and that resists shortening. low wall tension then easy for vascular smooth muscle to shorten and change diameter/radius of these vessels. then get back to Poiselles where r^4 det. flow of blood. can see v carefully regulated by vascular smooth muscle.
How do you control bp?
bc they are in series, by raising resistance in arterioles then raise resistance throughout whole system-how you control bp.
its the autonomic regulation (primary symp) of arterioles that regulates total peripheral resistance. so resistance meaning that blood runs off once ejected from heart into aorta and arterial system capillaries and venous system, rate at which runs off to venous system (bp declines between beats) is related to the total peripheral resistance of system and thats controlled by arterioles.
Describe resistances in parallel.
For resistances in parallel (B), the total resistance is less than any individual resistance.
Ex. Organs and vessels within a category of vessels (capillaries, etc.)
microcirculation- when R parallel to e/o bc of inverse relationship, if you add resistor to parallel network then you reduce, rather than increase overall resistance to blood flow bc more places for blood to flow
in series - if you increase resistance you increase total resistance
in parallel- if increase resistance or add resistor to system then reducing total resistance
Give an example of micro-circulation in heart/lungs.
when exercise you open up additional patterns for blood to flow in parallel in lungs and it reduces the overall resistance through pulmonary system
in heart capillary networks also open up… the small capillaries arranged in parallel and not all open at same time… during exercise you increase coronary or micro circulation in heart by opening up additional capillary beds. and that lowers overall resistance and allows more blood flow to get into those organs. main example-pulmonary system..don’t really have all capillaries open in resting conditions and when you exercise you do open up additional resistors in parallel and reduces resistance to blood flow through the lungs.
Describe the parallel and series arrangement of the circulatory system.
shows how system set up… heart set up in series. blood ejected from R atrium to R ventricle, goes to lungs. lungs are in series w the heart. then on L side of heart in series w e/o also.
in organ systems- lined up in parallel to large extent. percentage of CO that goes to each tissue..important to appreciate bc during exercise and hemorrhage blood flow to lots of these organs closed down due to sympathetic nerve activity. for ex. non vital organs like GI tract and renal system- 25 percent to GI under resting, 25 to renal under resting. during hemorrhage or exercise that blood flow cut off to large extent so 50 percent of blood shunted to coronaries, cerebral circulation, and to your lungs.
when exercise lots of blood to skeletal muscles. large amount of blood going to non vital organs and can be redistributed to vital organs under abnormal conditions. even in exercise blood really shunted to skeletal muscles and away from kidneys and GI.
Describe the cross sectional area and blood volume in capillaries. If they have such a large total cross sectional area, why do they have the smallest volume?
by far capillaries have largest cross sectional area but have v small amount of blood in them. Why? they’re v short. they’re only 1-2mm in length. v small volume of blood in capillaries even though huge cross sectional area. capillaries have slowest blood flow as a result of having largest cross sectional area. -goes back to diagram earlier where velocity of blood flow through vessel inversely related to cross sectional area. slowest blood flow in capillaries. Imp. bc thats where O and CO2 exchanged, so want blood moving slowly.
Where is the largest volume of blood?
as far as largest volume of blood- in veins. 60 percent of blood volume in veins- are a reservoir of blood. like carrying around transfusion.
How does a transfusion serve to increase bp? Describe the mechanism.
during hemorrhage that blood shunted from venous side to arterial side to increase bp and perfuse vital organs. that's what carrying blood around for. when give someone blood or saline, go into venous system, shift venous curve up, shunt more blood to heart, increase preload, increase CO, ultimately will increase bp. what trying to do- understand what means to give someone volume. has to go through venous system back to heart, heart pumps more blood bc of L tension relationship and you have larger bp. veins have larger cross sectional area too
Describe the blood volume in arteries.
blood volume amt compared to veins- tiny amount in arteries. 15-18 percent of blood in body is in arteries. why such small amount of blood? arterial system is designed, its low compliant, v stiff system, designed for low volume and high pressure. much easier to pressurize low volume. venous is very flexible high compliant system that holds a lot of volume and has v low pressure.
Where is resistance the largest? Smallest?
Resistance progressively increases and is the largest at the arterioles. Therefore, the largest drop in arterial pressure is across the resistance vessels, primarily the arterioles.
Although capillaries have the smallest diameter, the capillaries have the lowest total resistance because they have the largest total cross-sectional area. Therefore, the drop in pressure across the capillaries is relatively small.
showing total cross sectional area. total cross sectional area inversely related to velocity of blood flow. …applies to individual vessel or total cross sectional area - total cross sectional area of capillaries is highest and therefore v of blood flow through there is lowest. v high as comes out of aorta and slows down all way to capillaries.
Why is it that when shear rate or velocity slows, smaller vessels still have reduced viscosity?
in terms of viscosity when shear rate or velocity slows down that raises viscosity but bc small vessels have axial streaming is reduce viscosity even though blood flow is slow. 2 things offset e/o and have v low viscosity in these small vessels as blood going through. tie info together… as blood passes through capillaries, blood flow increases again as it flows back toward heart. increases again bc total cross sectional area getting smaller and smaller as go back to heart, less branching as go toward heart. so here’s total cross sectional area going up then back down again. inversely related
What is pulse pressure? When is the largest drop?
systolic pressure and diastolic pressure.. know when eject from heart systolic pressure is 120 and diastolic is 80. thats pulse pressure … can see as largest pressure drop in system, mean arterial pressure continuously dropping.. largest pressure drop is across arterioles. (losing E as blood tries to flow through v small vessels)
fact that vessels getting smaller and smaller in diameter means more and more blood flowing against the walls of these vessels- thats slowing down pressure dramatically. pressure being lost due to internal frictional resistance between lamina and between blood and wall of vessels
Why doesn't pressure drop more across capillaries?
bc so many of them and total cross sectional area is quite large even though vessels are tiny. pulse pressure is lost don't have systolic and diastolic pressure once get past small arteries into arterioles, then just continuous flow of blood. no pulse pressure across capillaries, just continuous flow of blood