Flashcards in CVM Week 5 - Cardiac Cycle Deck (28):
Compare the pressure in the right and left ventricle?
Right ventricle much lower in pressure than the left ventricle, but cardiac output is (almost 100%) the same in both sides
Why is it important that cardiac output is matched by both sides of the heart?
Enables proper circulation of blood without it backing up either in the venous system or in the pulmonary system. When it isn't matched, this is said to be heart failure
What period is the heart in when the ventricles are filling?
What is systole?
When the ventricles are ejecting blood
What is preload?
The degree of stretch in the ventricular wall by blood filling the ventricle.
The volume of blood in the ventricle will determine the preload
What is the frank starling law?
The increased stretch in the ventricles before they contract will enhance the contraction of the heart and allow greater volume of blood to be pumped out of the heart.
"The heart will accept and pump whatever makes it into the ventricles)
Why does the heart achieve greater contractile strength when there is a greater preload?
The greater volume of blood stretches the length of sarcomere, causing a greater distance that they can contract during excitation contraction coupling. This causes a greater force of contraction capable of ejecting more blood
What is afterload?
The resistance that the ventricles must overcome to pump blood into the arteries. Depends on arterial pressure and ease of blood flow through pulmonary and aortic valves
**remember blood flows from high to low pressure
What is end diastolic volume?
The amount of blood in the ventricle at the end of diastole. Essentially how much is there before the ventricle contracts
What is end systolic volume?
Amount of blood left in the ventricle following contraction (end of systole)
What is stroke volume?
Th difference between end diastolic volume and end systolic volume. Essentially it is how much blood in the ventricle before contraction minus how much blood is left in the ventricle following the contraction.
What is cardiac output?
A rate of blood being pumped out of the heart in litres per minute.
Cardiac output= stroke volume x heart rate
In the 'lub dub' sound of a heartbeat, what sound is the 'lub'?
Closing of mitral valve
What is the 'dub' sounds?
The closing of the aortic valve
How can you increase cardiac output?
By increasing heart rate or stroke volume?
How can you increase stroke volume?
By increasing the preloading of the ventricles (through greater venous return) Increased preload equals increased muscle contractility.
Increased cardiac muscle contractility is also achieved via sympathetic stimulation and actions of catecholamines
How could decreased arterial pressure increase stroke volume?
It would decrease afterload (the pressure that the ventricle would have to overcome to push blood into the artery) and so blood would flow more easily out of the heart, which increases the output.
What is isovolumetric ventricular contraction?
When there is the beginning of the ventricular contraction which pulls the AV valves closed, but not enough pressure has built up to push the semilunar valves open. There is an increase in pressure but no change in volume during isovolumetric contraction
What occurs in ventricular ejection?
Ventricular pressure rises as a result of contraction, which reaches a point where it will exceed the pressure in the arteries and force semilunar valves open and blood will flow into the aorta and pulmonary trunk.
What occurs in isovolumetric relaxation?
Ventricles relax, pressure in the ventricles begin to fall and blood flows back into the cusps of the semilunar valves and shuts them. The AV valves are still close as the papillary muscles still are relaxing and they haven't opened up yet
At what stage of the cardiac cycle does filling of the ventricles occur?
In late diastole - the AV valves open when the ventricles have relaxed and blood flows through from high pressure to low pressure. Atrial systole follows this and pushes the last additional blood into the ventricles before systole begins again
Why is the pressure in the aorta lowest just before the aortic valve opens following ventricular systole?
Blood in the aorta gets pushed to all the peripheral capillary beds where it filters out to the interstitial spaces and tissues, decreases pressure. This pressure decreases from when the aortic valve closes until it opens again.
What is the dicrotic notch in aortic pressure? (Hint: it occurs just after the aortic semilunar valve closes)
Dicrotic notch is the slight drop in aortic pressure following the closure of the semilunar valve. This is due to a small bit of back flow as the valve is closing. When it is fully close, the blood pushing back against the valve causes a slight increase in pressure
Why could a patient with recurrent MI which has causes scar tissue to replace muscle have a decreased cardiac output?
The scar tissue which replaces the muscle doesn't contract. This will decrease the contractility of the heart, and reduce the pressure that the ventricles can produce. This will reduce the stroke volume of the heart. Heart will work harder to compensate by having a higher HR.
What is a baroreceptor?
A stretch receptor (neuron) located on the aortic arch and in carotid arteries which senses blood pressure by distortion changes in its receptor membrane
How does a baroreceptor act when there is low blood pressure?
They stop firing impulses when blood pressure drops, which causes the autonomic nervous system to send impulses to the heart to increase heart rate and stroke volume to increase blood pressure and vasoconstriction
Explain the process of why someone would faint getting out of a hot bath?
Increased temperature = vasodilation = decreased blood pressure
When lying down heart output is decreased as it doesn't have to work against gravity to pump blood around the body