Circulation Flashcards
Explain Poiseuille’s law and how it relates blood flow, pressure and resistance.
Flow=pressure/resistance. To change flow, have to either increase pressure (gradient) or decrease resistance. FLOW is directly related to r^4, while resistance is inversely related to r^4. Resistance also directly proportional to viscosity and length.
Pressure gradient tends to stay pretty constant, so changing r^4 (via arteriolar vasoconstriction or dilation) is most important determinant.
Define viscosity and how it changes with vessel diameter and hematocrit.
Shear stress/shear rate. It is internal frictional resistance of fluid in a column.
Hct: More hct=more more viscosity and slower flow
Diameter: Smaller diameter=smaller viscosity and faster flow (due to axial streaming and plasma skimming–RBCs tend to congregate in axial laminae, so this will be smaller in smaller vessels so you have more relative plasma and less viscosity).
Explain how hematocrit changes with vessel diameter.
Have more hct in larger vessels due to axial streaming.
Smaller vessels have fewer RBCs due to plasma skimming.
Define laminar and turbulent blood flow.
Laminar: Flows in individual columns that make a parabola.
Turbulent: Flows chaotically. Noisy.
Define Reynold’s number and how each of its parameters contributes to the development of turbulent blood flow.
Indicates propensity for turbulent flow. =densitydiametervelocity/viscosity.
Higher number=higher chance for turbulent flow.
The smaller the vessel, the faster the flow and the more likely you are to have turbulent flow (big increase in velocity for given diameter (r^4)).
Aorta a likely place for turbulent flow because it is both high in cross-sectional area and has high velocity.
Understand that turbulent blood flow contributes to heart sounds, murmurs and endothelial cell damage.
Also, bruits. Anything going through a stenosis could become turbulent and audible. Damages endothelium and can give you dissecting aneurysm.
Define Bernoulli’s principle and its application to the circulatory system.
Total nrg is conserved–potential+kinetic. In a stenotic system, PE (pressure) is converted to KE (flow). Faster flow=higher likelihood of turbulent flow. More important in sending flow down pressure gradient is sending flow down total nrg gradient.
Define the Laplace relationship and how wall tension affects the function of dilated hearts, capillaries, and aneurysms.
Wall tension=pressure*radius/wall thickness
So, small vessel=small wall tension (capillaries).
Dilated heart: Larger radius creates more wall tension. Shortening impeded, AL increased.
Aneurysm: Larger radius creates more wall tension, flow slowed down, more transmural pressure will eventually cause it to rupture.
Explain how wall tension and the anatomy of arterioles and precapillary sphincters (large wall thickness/lumen diameter ratio) operates in normal regulation of vascular resistance.
The higher the wall thickness/lumen diameter ratio, the more control over vessel diameter (and thus blood flow).
Define the relationships between velocity of blood flow and vessel cross sectional area.
Smaller area=faster flow (by factor of r^4)
Explain series and parallel resistances in the circulatory system.
Series: Resistances add up to total resistance. Tends to be in series until you get to viscera. Arterioles are in series, so change resistance in 1 change resistance of whole system.
Parallel: Total resistance is less than each individual resistance. Seen in capillary beds and viscera.
Define how velocity of blood flow, and pressures change throughout the circulatory system in relation to changes in total cross-section area.
Total cross-sectional area increase through capillaries, then decreases again in venules up through veins.
This means that Velocity decreases until you get into venues, where it starts going back up again.
Pressure continually goes down throughout the system
Explain the pulse pressure profiles throughout the circulatory system.
As you get further from heart in large arteries, systolic goes up and diastolic goes down, resulting in larger PP and lower mean arterial pressure (determined more by diastolic).
Due to decreases in arterial compliance the further you get.
Lose PP in arterioles and don’t get it back until atria.
Explain how elastin, smooth muscle and collagen function as structural components of
the vascular wall.
Elastin is the most elastic and responsible for most of arterial compliance. Within tunica intima (IEL) and media (EEL). NOT present in veins.
Smooth muscle: Somewhat compliant, in tunica media. Not as well developed in veins.
Collagen: Very uncompliant, in tunica medida. More pronounced in veins.
Define compliance.
Change in pressure for a given change in volume. C=dV/dP. Basically, how much the pressure in a vessel will go up with a given change in volume.
Explain how vessel wall compliance affects arterial pressures.
If you take away compliance (say by elastin becoming less elastic), then you will raise systolic pressure (aorta won’t distend when blood flows into it) and lower diastolic pressure (won’t recoil when blood leaves).
Put another way, to apply Bernoulli, in normal aorta, PE is converted to KE to move out walls of aorta when blood ejected into vessel. That pressure has nowhere to go in case of loss of elasticity, and will stay as PE (pressure) in artery.
Explain the windkessel (hydraulic filtering) properties of the aorta.
In normally compliant aorta, part of SV stored in artery as it is stretched during systole.
Once diastole hits, recoil of aorta forces that SV that was stored to leave, creating continuous flow (lower systolic pressure).
In non-compliant aorta, full SV must be ejected during systole (lower diastolic pressure because nothing in aorta at diastole).
Define the relationship between velocity, flow and vessel cross sectional area.
As cross sectional area increases, velocity decreases.
As cross sectional are a increases, flow increases.
Define the importance of wall/lumen diameter ratio to regulation of arterial pressure.
Higher ratio=more control over vessel flow. Biggest ratios are pre capillary sphincters and arterioles and thus these regulate flow the most.
Define the pressure pulse.
Pressure wave propagated down vessel wall. The less compliant, the faster the speed. Pressure strengths will feel different at different areas you take your pulse.
Define the physiological and physical factors that determine mean arterial pressure.
Physiological: CO (primarily regulated by ANS) and peripheral resistance (ANS that can be overridden by local control).
Physical: Blood volume (higher volume=more pressure) and arterial compliance (determined by age, location, volume,).
Define the primary determinants of systolic and diastolic pressures.
Systolic: CO, compliance, volume.
Diastolic: TPR, compliance (lowers it)
Explain how arterial compliance affects systolic and diastolic arterial pressures.
Increasing compliance increases systolic and decreases diastolic pressure.
Explain the factors that determine and regulate peripheral arterial resistance.
Blood viscosity: Only occurs in pathological conditions (blood doping, anemia).
Arteriolar radius: Determined by a bunch of stuff: Extrinsic control (hormones, baroreceptor, sympathetic) and local (EDRF, metabolites, myogenic response).
Explain how the autonomic nervous system regulates mean arterial pressure.
Increases HR and contractility, which increase SV and CO, and thus BP.
Increase venoconstriction to mediate more return to heart and increase SV
Increase arteriole constriction, which increases TPR to get blood to more vital organs
Para: Decrease HR (hyperpolarize MbP to and elongate refractory period).
Explain the cardiovascular adjustments and underlying mechanisms that operate during exercise.
- Increased HR and contractility
- Vasoconstriction to areas not being worked (kidney, splanchnics, etc)
- Local metabolic vasodilation
- Capillaries open
- Enhanced O2 extraction in skeletal muscle but NOT in heart (dissociation curve shifts, O2 held less tightly by Hg)
- Increase in venous return due to venoconstriction, respiratory pump, muscle pump.
- Pulse pressure widens: Increase in systolic pressure due primarily to increase in SV, diastolic determined primarily by changes to TPR, which should remain relatively constant.
