Cardiac Cycle Flashcards
Why is the cardiac cycle a cycle?
Heart is a cyclic pump, one sec it is doing something and a little later will end up back at square one and does so forever
What is happening in the diastolic period right after the ventricle has contracted until the atria contract?
The vessel valves are closed since the pressure has dropped in the ventricles. They are relaxed and the atria are relaxed, but they never stop filling, no valve there, so the pressure is building up in them, the ventricle pressure is near 0 so the ventricles are filling up, the AV valves are open. The pressure difference is very small but just enough to get blood flow from the atria to the ventricle. Then the atria contract at the next beat and this causes more blood to be dumped at a faster rate into the ventricle. Ventricles are filled in two phases, long phase and then the atria contract and the cycle restarts with ventricular contraction.
Once the atria contract the ventricles are quick to follow, what happens at this stage of the cardiac cycle?
Systole begins
Once the ventricles contract, the AV valves close due to the pressure increase (like in 10 ms, so quick) (pressure in ventricles > pressure in atria) even if just a tiny bit because pressure difference was so small to begin with anyway, and this is the beginning of the isovolumetric ventricular contraction phase. The volume is fixed since the valves are closed but the pressure is increasing from the contraction.
The pressure goes from 0 to 100-120 real quick and when it just exceeds the pressure in the great arteries, the vessel valves open, this is the beginning of the ejection phase, pressure in the ventricles still increasing since still contracting but eventually muscles relax and pressure drops so fast
What happens at the beginning of diastole?
As ventricular muscles relax, Pventricle < P(great arteries), so vessel valves close and since the AV valves are closed as well this is the isovolumetric ventricular relaxation phase, both valves are closed as pressure falls all the way to 0 until just smaller than Patria and the AV valves open again and we are back in the ventricular filling phase
What are some insightful details that we can get about the cardiac cycle using Wiggers’ diagram?
- Ventricular contraction right during QRS => plateau Ca2+ entering to contract, right before isovolumetric ventricular contraction phase
- Isovolumetric start when the valves close and end as soon as the valves opens, we can see a plateau in volume curve during this period
- In the rest period most of the volume enters before the atrial contraction, so atrial contraction is not the main player for filling ventricles but helps boost rate of filling, 10s of millions of people walking around with atrial fibrillation => most common cause of arrhythmia, not big burden cuz not major player of ventricular filling, people still have a good cardiac output
- When looking at the volume curve we see that the atrial kick allows ventricle to fill at a faster rate thx to atrial contraction and then the end diastolic volume is reached during the isovolumetric ventricular contraction phase (max amount of blood in ventricle) and the end systolic volume is the volume at the end of systole and is reached during the isovolumetric ventricular relaxation phase (EDV - ESV = SV)
- The 1st heart sound is the atrial valve closing (isovolumetric contraction phase), systole starts here and stops at the 2nd heart sound which is the closing of the aortic valve (beginning isovolumetric relaxation phase)
- Systole is iso contraction + ejection phase
- Diastole is iso relaxation + ventricular filling
Reminder of what the stroke volume is?
Blood pumped out at every heartbeat, for each ventricle but mostly refers to left though
SV = EDV - ESV = 120 - 50 = 70 mL (today probably about 100 mL since people are bigger)
What is the ejection fraction?
- Percentage of blood that is expelled
- Ejection fraction = SV/EDV = 70/120 = 0.6 (60%)
- Drops if you have a heart attack and lose a good portion of heart muscle => heart failure
Reminder of what the cardiac output is?
- Volume/minute pumped to the body = HR (beat/min) x SV (volume/beat)
- CO = 70 bpm x 70 mL = 5 L/min
What is the difference of the right heart cardiac cycle compared to the left heart cardiac cycle?
- One dif is the right vs left anatomy
- Also the max pressure reached in the ventricle is only about 30 mm Hg
- Other than that everything is pretty similar and the valves open and close at the same time as the eft heart valves (sound is both valves together)
What is Starling’s law of the heart (Frank-Starling mechanism)?
- If we increase the pressure in the atrium, the EDV increases and the SV increases because the volume will stretch the walls of the ventricle more so the force of contraction increases
- This stretch before the start of contraction is also known as the pre-load, but it is hard to make a direct measurement so we use other variables like the EDV which can measure and the Pra
What is a fact about venules that you may not know (from table 12.3)?
Capacitance vessels that are sites of migration of leukocytes from the blood into tissues during inflammation and infection
What is in the plasma component of blood?
Liquid portion of blood that contains dissolved nutrient, ions, waste, gases, and other substances. Its composition equilibrates with that of the interstitial fluid at the capillaries.
What are the main cells in blood?
Includes erythrocytes that function mainly in gas transport, leukocytes that function in immune defenses, and platelets (cell fragments) for blood clotting.
