Cardiac Cycle
When do the S1 sound and S2 sound occur? What valves close causing these sounds?
S1 - Isovolumetric Contraction Phase - Atrioventricular Valves close
S2 - Isovolumetric Relaxation Phase - Semilunar Valves close
If a patient has an EDV of 160 mL/beat, an ESV of 80 mL/beat and a heart rate of 88 beat/min, what is their cardiac output?
SV = EDV - ESV
SV = 160 - 80 = 80 mL/beat
CO = HR x SV
CO = 88 beat/min x 80 mL/beat = 7040 mL/min
(This is pretty high for CO)
What hormones are involved with peripheral resistance (PR)?
Epinephrine/norepinephrine: causes vasoconstriction which increases PR which increases BP
Angiotensin-II: causes vasoconstriction which increases PR which increases BP
ANP: causes vasodilation which decreases PR which decreases BP
What is mean arterial pressure (MAP)? What is pulse pressure?
MAP: The weighted average of systolic & diastolic pressure.
Pulse Pressure: The difference between systolic and diastolic pressures. This is measured by:
Pulse = systolic pressure - diastolic pressure
What is the purpose of precapillary sphincters?
Located where the metarteriole meets the true capillary - circular muscles that contract to blow flow and relax to allow flow.
This allows for blood to either enter the capillary as needed or flow in the central vessel (the thoroughfare channel) towards the venule if it's not needed.
*Based on the needs of the tissues*
During what phases of the cycle are the ventricles in systole?
During what phases of the cycle are the atria in systole?
Ventricles: Starts systole in isovolumetric contraction phase and remains in systole throughout the ventricular ejection phase. They return to diastole in the isovolumetric relaxation phase.
Atria: In systole only within the ventricular filling phase (and even then only for a part of it). Helps fill ventricles with blood.
Name the 3 factors affecting stroke volume and describe their differences.
* relates to Frank-Starling law *
2. Contractility - hearts intrinsic pumping ability independent from preload. Relates more with the muscles ability rather than the sarcomeres. Higher contractility => higher stroke volume.
3. Afterload - force ventricles have to overcome in order to eject blood out of the heart. Higher afterload => higher pressure in arteries => lower stroke volume.
How do the different nervous systems regulate cardiac output?
Sympathetic NS:
- uses epinephrine & norepinephrine
- positive chronotropic effects (increases HR => increases CO)
- positive inotropic effects (increases contractility => increases SV => increases CO)
Parasympathetic NS:
- uses acetylcholine (ACh)
- negative chronotropic effects (decreases HR => decreases cardiac output)
- negative inotropic effects (decreases contractility => decreases SV => decreases CO)
*PSNS has relatively weak inotropic effects though
What four factors of peripheral resistance have we discussed and how do they alter blood flow?
PR:
- blood vessel length: as length increases, PR increases, lowering blood flow
- vessel diameter: as diameter increases, PR decreases, raising blood flow
- blood viscosity: as viscosity increases, PR increases, lowering blood flow
- obstructions in vessels: more obstructions will cause PR to increase, lowering blood flow
What is the difference between filtration and absorption?
Filtration: water exiting the capillary due to high hydrostatic pressure of water within the capillary versus low hydrostatic pressure of water outside the capillary and into the interstitial fluid of the tissue. More filtration will occur at the arteriole end than the venule end of the capillary.
Absorption: water being drawn into the capillary due to the osmotic pressure of the capillary being higher than the interstitial fluid of the tissue outside of the capillary. The water is drawn to more solutes, which exist in the capillary.
Describe what end-diastolic volume and end-systolic volume is. What is their relationship?
End-Diastolic Volume (EDV): the most amount of blood seen in the ventricles. Is measured at the end of the ventricular filling phase, before the ventricles begin systole.
End-Systolic Volume (ESV): the least amount of blood seen in the ventricles. Is measured at the end of the ventricular ejection phase, as the blood has just been pushed out to the arteries.
Both describe the minimum and maximum amount of blood in the ventricles during a cycle. By subtracting the ESV from the EDV, we get a positive number that represents the stroke volume (SV), which is the amount of blood ejected from the heart per cardiac cycle:
SV = EDV - ESV
If a patient has an EDV of 123 mL/beat, an ESV of 64 mL/beat and a heart rate of 61 beat/min, what is their cardiac output?
SV = EDV - ESV
SV = 123 - 64 = 59 mL/beat
CO = HR x SV
CO = 61 beat/min x 59 mL/beat = 3599 mL/min
(This is abnormally low for CO)
Describe the baroreceptor reflex in the context of high blood pressue.
Baroreceptors are receptors that are sensitive to pressure changes. They are located in the carotid and aortic sinus and thus can detect these changes due to their proximity to the heart. The baroreceptor reflex refers to how these changes are read and managed.
In the case of high blood pressure, the baroreceptors would detect the higher pressure and send an impulse via the glossopharyngeal nerve to the medulla oblongata in the brainstem to then decrease BP. This is done by inhibiting the sympathetic NS activity, decreasing HR and peripheral resistance, lowering CO and thus effectively lowering BP.
Describe the 3 factors contributing to the maintenance of blood pressure.
Peripheral resistance - elements contributing to how fast and easily blood can flow. Nervous and endocrine system contribute to this.
Cardiac output - the volume of blood pumped out per minute. Nervous and endocrine system contribute to this.
Blood volume - the total volume of blood present in the vasculature. ONLY the endocrine system contributes to this, not the nervous system.
Compare & contrast between myogenic and metabolic autoregulation of perfusion.
Myogenic: goal is to maintain perfusion as the systemic BP changes
- increased stretch of arterioles due to high BP results in muscle contraction/vasoconstriction
- this mechanism returns perfusion back to normal level
Metabolic: goal is to match perfusion to metabolic needs of tissue
- increased concentrations of metabolic byproducts due to high metabolic activity results in vasodilation
- this mechanism ensures that no shortage of oxygen/nutrients occur, as well as that no extreme excess oxygen/nutrients are used
Both: Alter peripheral resistance by changing diameter of arteriole in order to change perfusion.
(Remember, as diameter increases, PR decreases, which then increases blood flow and perfusion. As diameter decrease, PR increases, which then decreases blood flow and perfusion)
Describe the pressure gradients occurring between the atria & ventricles and/or the ventricles & arteries for each phase of the cardiac cycle. How do the valves act in each phase?
Ventricular Filling Phase:
Atria has high pressure, ventricles have low pressure. Blood moves from atria to ventricles now since AV valves are open.
Isovolumetric Contraction Phase:
Ventricles have higher pressure now, more than atria. AV valves close to prevent back flow due to the change in pressure.
Ventricular Ejection Phase:
Ventricles have higher pressure than arteries and atria. AV valves closed, but SL valves open to let blood flow in correct direction. Blood moves from ventricles to arteries.
Isovolumetric Relaxation Phase:
Arteries now have higher pressure than ventricles, so SL valves close to prevent back flow. Ventricles are still at a higher pressure than the atria so the AV valves remain closed.
What is the difference between inotropic and chronotropic effects?
Inotropic - describes something affecting contractility.
Chronotropic - describes something affecting heart rate.
If a person was extremely active, how would the metabolic mechanism of autoregulation work to match the active tissue's metabolic needs at that moment?
The goal with the metabolic mechanism is to change perfusion to match the needs of the tissue at that moment in time. Thus, since this individual is high in activity, it can be assumed that they'll be needing more nutrients and oxygen to sufficiently reach and replenish the active tissue.
In this case, vasodilation would occur as to decrease peripheral resistance and to increase overall flow of blood. This would allow for increased perfusion in the area, successfully delivering the nutrients and oxygen as needed.
The exact opposite is also true with everything swapped out (low metabolic activity [i.e. someone is laying down] -> vasoconstriction -> increased resistance -> decreased perfusion).
How does the nervous system regulate blood pressure?
Sympathetic NS: increases blood pressure by increasing both HR & contractility, changes PR by causing widespread vasoconstriction, increasing cardiac output. Works directly.
Parasympathetic NS: decreases blood pressure by decreasing HR & contractility directly (since the CNS will directly innervate the heart) which decreases cardiac output. Indirectly changes PR by causing widespread vasodilation. Works indirectly by blocking signals of SNS neurons on blood vessels which would normally contract otherwise.
What is hydrostatic pressure? What is osmotic pressure?
Hydrostatic Pressure (HP) - The pressure that fluid exerts on the wall of its container, like blood in blood vessels. Has a similar gradient to blood pressure (moves from high pressure to low pressure).
Osmotic Pressure (OP) - How water moves from low solute concentration to higher solute concentration. One way to picture this is as the solutes pulling the water closer to them like a tug-of-war. The concentration with more power (in this case, the higher solute concentration side) will pull the water more easily.
Both are opposing pressures to each other.
Which phase is described here:
The ventricles ejected blood into the arteries here. Atria are in diastole while ventricles are in systole, hence pressure is still high within the ventricles. Since pressure is high in ventricles and low in arteries, blood flows to the arteries. AV valves are still closed while SL valves open. This is also where we can now measure the ESV since the minimum amount of blood is present.
Ventricular ejection phase!
How does the endocrine system regulate cardiac output?
Epinephrine/norepinephrine/thyroid hormone/glucagon:
- increases contractility to increase CO
- done by increasing SV and increasing HR (pos. chronotropic/inotropic effecrs)
Aldosterone & ADH:
- increases blood volume (BV) to increase CO
- done by influencing water volume to be higher so BV is higher, increasing preload and stroke volume
ANP
- decreases BV to decrease CO
- done by ridding water so BV lowers, causing preload and stroke volume to decrease
What is the goal with the myogenic mechanism of perfusion? How is this accomplished?
To help maintain consistent perfusion when blood pressure is changing. Essentially, if blood pressure were to decrease, the perfusion of blood would also decrease. Thus, the myogenic mechanism would cause vasodilation to decrease peripheral resistance and to increase perfusion. The tissues would still then be receiving the same amount of perfusion had the blood pressure not dropped.
The same is applied with everything switched ( increased BP -> increased perfusion -> vasoconstriction -> increased resistance -> decreased perfusion now).
It may be helpful to you to consider the [flow = pressure gradient / resistance] relationship.
If a persons blood pressure was extremely high, how would the nervous system and the endocrine system work to lower it back to normal?
The parasympathetic NS would have both direct and indirect ways of lowering blood pressure. Directly, heart rate would decrease (chronotropic effect) and contractility would decrease (weak inotropic effect) causing low stroke volume and low cardiac output. This leads to a decrease in blood pressure. Indirectly, the parasympathetic NS would inhibit the sympathetic neurons from telling the blood vessels to contract, causing vasodilation and decreasing blood pressure.
The endocrine system would alter the peripheral resistance using ANP, which would cause vasodilation (hence decreasing PR) and lowering BP. ANP would also lower blood volume as it stimulate water loss, which would also lower BP.
What is net filtration pressure?
The overall change occurring due to differing pressures within the capillary is measured using net filtration pressure (NFP). Helps determine which pressure is winning at each end of the capillary (arteriole vs venule).
Both hydrostatic pressure and osmotic pressure are used in determining the NFP by subtracting the OP from HP:
NFP = HP - OP
If HP is higher than OP, water leaves the capillary by filtration. (NFP>0)
If OP is higher than HP, water enters the capillary by absorption. (NFP<0)
*COP is colloid osmotic pressure - refers to the OP generated by albumin specifically*