CVM Week 5 - Cardiac Cycle

Question 0

Why is it important that cardiac output is matched by both sides of the heart?

Answer 0

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

Question 1

Compare the pressure in the right and left ventricle?

Answer 1

Right ventricle much lower in pressure than the left ventricle, but cardiac output is (almost 100%) the same in both sides

Question 2

What period is the heart in when the ventricles are filling?

Answer 2

Diastole

Question 3

What is systole?

Answer 3

When the ventricles are ejecting blood

Question 4

What is preload?

Answer 4

The degree of stretch in the ventricular wall by blood filling the ventricle.
The volume of blood in the ventricle will determine the preload

Question 5

What is the frank starling law?

Answer 5

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)

Question 6

Why does the heart achieve greater contractile strength when there is a greater preload?

Answer 6

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

Question 7

What is afterload?

Answer 7

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

Question 8

What is end diastolic volume?

Answer 8

The amount of blood in the ventricle at the end of diastole. Essentially how much is there before the ventricle contracts

Question 9

What is end systolic volume?

Answer 9

Amount of blood left in the ventricle following contraction (end of systole)

Question 10

What is stroke volume?

Answer 10

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.

Question 11

What is cardiac output?

Answer 11

A rate of blood being pumped out of the heart in litres per minute.
Cardiac output= stroke volume x heart rate

Question 12

In the ‘lub dub’ sound of a heartbeat, what sound is the ‘lub’?

Answer 12

Closing of mitral valve

Question 13

What is the ‘dub’ sounds?

Answer 13

The closing of the aortic valve

Question 14

How can you increase cardiac output?

Answer 14

By increasing heart rate or stroke volume?

Question 15

How can you increase stroke volume?

Answer 15

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

Question 16

How could decreased arterial pressure increase stroke volume?

Answer 16

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.

Question 17

What is isovolumetric ventricular contraction?

Answer 17

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

Question 18

What occurs in ventricular ejection?

Answer 18

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.

Question 19

What occurs in isovolumetric relaxation?

Answer 19

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

Question 20

At what stage of the cardiac cycle does filling of the ventricles occur?

Answer 20

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

Question 21

Why is the pressure in the aorta lowest just before the aortic valve opens following ventricular systole?

Answer 21

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.

Question 22

What is the dicrotic notch in aortic pressure? (Hint: it occurs just after the aortic semilunar valve closes)

Answer 22

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

Question 23

Why could a patient with recurrent MI which has causes scar tissue to replace muscle have a decreased cardiac output?

Answer 23

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.

Question 24

What is a baroreceptor?

Answer 24

A stretch receptor (neuron) located on the aortic arch and in carotid arteries which senses blood pressure by distortion changes in its receptor membrane

Question 25

How does a baroreceptor act when there is low blood pressure?

Answer 25

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

Question 26

Explain the process of why someone would faint getting out of a hot bath?

Answer 26

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

Question 27

What is a chemoreceptor?

Answer 27

Another type of neuron which is located in aorta and carotids. Sense levels of CO2, O2 and blood pH. Impulses directed to medulla which will then dictate whether inhibition of the parasympathetic system occurs. This will cause increased heart rate, and also increased respiration rate