Cardiovascular: Left and Right Pumps of the Heart L6 Flashcards
The heart is considered to be two pumps in what circuit?
Series circuit
What is the cardiac cycle?
One complete full heart beat.
Do the right and left sides of the heart contract together or separately?
Together.
How are the ventricles filled?
Filling of the ventricles mainly occurs passively but blood is topped up through synchronised contraction of the left and right atria. This stretches the ventricles priming them for contraction.
Give a brief description of the two phases in the cardiac cycle? Which one is more prevalent?
Systole is when the ventricles of the heart are contracting. Pressure in the heart is at maximum. Diastole is when the ventricles are relaxing. Passive filling occurs and the heart is at it’s lowest pressure. The heart spends more time in diastole than systole, about 60:40 at rest.
How does the shape of the heart increase efficiency of contraction?
The heart muscle is arranged in a helical pattern to increase the efficiency of contraction. It twists and contorts as it contracts. The heart contracts like a towel being wrung.
How does the opening/closing of valves relate to atria/ventricular contraction?
When the atria contracts, the AV valves are open, but the semilunar valves are closed. The space the blood is in is now lower which drives up pressure in ventricles (Diastole).
In ventricular contraction, the AV valves are closed to prevent backflow, but the semilunar valves are open allowing blood to flow into aorta and pulmonary trunk (Systole).
Explain the cellular mechanism for cardiac contraction.
An increase cytosolic Ca2+ levels, induces Ca2+ release from sarcoplasmic reticulum. Ca2+ binds to troponin, moves tropomyosin. Actin binding site revealed. Myosin binds forming the cross-bridge. Actin-Myosin filaments slide relative to each other (myosin pulls on actin). Sarcomere shortens, force is generated. Every myocyte activated each heart beat.
How to increase the force of contraction?
Each cardiomyocyte is activated during each beat. Extent of cross-bridges formed not maximised at rest. The higher the cystolic level of Ca2+, the higher the number of cross-bridges formed, the stronger the force of contraction.
Explain the cellular mechanism for cardiac relaxation.
ATP binds to myosin. Decrease in cystolic Ca2+ levels, Ca2+ goes back into sarcoplasmic reticulum. Cross bridge release, actin and myosin. Decrease in force. All cardiac myocytes relax each heart beat.
Within the 2 main phases, discuss the processes of the cardiac cycle.
(Note: this is a cycle, there is no true first phase)
- Atrial systole - contracting atria flows blood through AV valve into ventricles, the semilunar valves are closed. Push maximum blood (on top of the blood that passively flowed) into ventricles to push the maximal amount of blood into arteries.
- Isovolumetric ventricular contraction (Systole)- The atria is no longer contracting. AV valves close, no backflow to atria, Semilunar still closed. Blood is effectively moving no where. Ventricles are contracting. Pressure on blood is hugely increasing. Isovolumetric = Same volume of blood. When pressure of ventricles has exceeded pressure of aorta+pulmonary valves, the semilunar valves will open.
- Ejection - The pressure in the ventricles have exceeded the pressure in the aorta and pulmonary valves, then the semilunar valves will open. Blood rushes out of the ventricles into the aorta and pulmonary trunk. Some blood remains in the heart (approx 40%). Once enough blood has entered the vessels it will push back on the semilunar valves to close them.
- Isovolumetric ventricular relaxation (Diastole) - The opposite of IVC. Both valves are closed. Most blood has been ejected from the ventricles. Volume of blood remains the same but ventricles widen as they relax, causing pressure to decrease. During this phase, blood from the pulmonary and systemic circulations is returning to the atria. This causes a pressure build-up. Once the pressure in the atria exceeds that of the ventricles, the AV valves will open.
- Passive ventricular filling - Blood passively flows through the opened AV valves, from atria to ventricles.
Discuss the systole phase (contractile period).
Atrial systole - contracting atria flows blood through AV valve into ventricles, the semilunar valves are closed. Push maximum blood (on top of the blood that passively flowed) into ventricles to push the maximal amount of blood into arteries.
Isovolumetric ventricular contraction (Systole)- The atria is no longer contracting. AV valves close, no backflow to atria, Semilunar still closed. Blood is effectively moving no where. Ventricles are contracting. Pressure on blood is hugely increasing. Isovolumetric = Same volume of blood. When pressure of ventricles has exceeded pressure of aorta+pulmonary valves, the semilunar valves will open.
Discuss the diastole phase (relaxation period).
Isovolumetric ventricular relaxation (Diastole) - The opposite of IVC. Both valves are closed. Most blood has been ejected from the ventricles. Volume of blood remains the same but ventricles widen as they relax, causing pressure to decrease. During this phase, blood from the pulmonary and systemic circulations is returning to the atria. This causes a pressure build-up. Once the pressure in the atria exceeds that of the ventricles, the AV valves will open.
Passive ventricular filling - Blood passively flows through the opened AV valves, from atria to ventricles.
Why is the left ventricle more powerful than the right ventricle?
The left ventricle requires greater power because the systemic circulation is much larger, involves going around the entire body, therefore has a much greater resistance than the pulmonary circulation. This is reflected anatomically, the wall of the left ventricle is much bigger than the right (3 times bigger). Because left and right pumps are in series, it is important that flow (Q) is the same on both sides. Because Q=P/R, the left pump must generate more pressure (than right pump) to compensate for increased resistance so that flow remains the same.
Describe what is meant by pulsatile blood flow.
The flow of blood is pulsatile in the great arteries, although continuous by the time blood reaches the capillaries, this is because of the elasticity of the arteries. The peripheral pulse is felt as a transmitted force travelling along the wall of the artery, ahead of the flow of blood.
