CS: Cardiac Cycle

Question 1

Where is the heart located?

Answer 1

In the mediastinum in the thoracic cavity

Question 2

What is the mediastinum?

Answer 2

Space between the lungs

Question 3

How is the heart separated from the other structures in the mediastinum?

Answer 3

By a tough membrane known as the pericardium that sits in the pericardial cavity

Question 4

Where is the heart positioned in the lungs?

Answer 4

In the cardiac notch seen in the left lung

Question 5

What are the 4 valves that regulate the movement of blood through the heart?

Answer 5

1. Right atrioventricular valve (tricuspid)
2. Aortic semilunar valve
3. Left atrioventricular valve (bicuspid)
4. Pulmonary semilunar valve

Question 6

Describe the action of the right atrioventricular valve

Answer 6

Regulates the movement of blood between the right atrium and right ventricle. When the pressure in the right atrium is greater than the pressure in the right ventricle, the valve opens to allow the flow of blood into the ventricle.

Question 7

Describe the action of the aortic semilunar valve

Answer 7

Regulates the movement of blood between the right ventricle and the aorta for transport to the lungs. When the press in the right ventricle is greater than the pressure in the aorta, the valve opens to allow the flow of blood into the aorta.

Question 8

Describe the action of the left atrioventricular valve

Answer 8

Regulates the movement of blood between the left atrium and left ventricle. When the pressure in the left atrium is greater than the pressure in the left ventricle, the valve opens to allow the flow of blood into the ventricle.

Question 9

Describe the action of the pulmonary semilunar valve

Answer 9

Regulates the movement of blood between the left ventricle and the pulmonary artery for transport around the body. When the pressure in the left ventricle is greater than the pressure in pulmonary artery, the valve opens to allow the flow of blood into the pulmonary artery.

Question 10

What is a significant feature of valves that make them suited to their role?

Answer 10

They are unidirectional; they allow the flow of blood in one-direction through the heart to prevent back flow.

Question 11

How is blood flow controlled?

Answer 11

Blood flow is controlled by pressure changes which reflect the alternating contraction and relaxation of the heart. Blood moves along pressure gradients from high to low.

Question 12

What are the 7 stages of the cardiac cycle?

Answer 12

1. Atrial systole
2. Isovolumetric contraction
3. Rapid ejection
4. Reduced ejection
5. Isovolumetric relaxation
6. Rapid ventricular filling
7. Reduced ventricular filling

Question 13

What happens during the atrial systole stage of the cardiac cycle?

Answer 13

Contraction of the atria follows depolarization, represented by the P wave of the ECG. As the atrial muscles contract from the superior portion of the atria toward the atrioventricular septum, atrial pressure rises (‘a’ wave) and blood is pumped into the ventricles through the open atrioventricular valves. Contraction of atria finishes before the ventricle contracts.

Question 14

What happens during the isovolumetric contraction stage of the cardiac cycle?

Answer 14

Interval between the atrioventricular valve closing and the opening of the semilunar valves. Atrioventricular valve closes when ventricular pressure exceeds atrial pressure; ventricle pressure increases, but volumes remains the same, to match the pressure in the aorta/pulmonary artery.
Ventricular systole follows the depolarization of the ventricles and is represented by the QRS complex in the ECG.

Question 15

What happens during the rapid ejection stage of the cardiac cycle?

Answer 15

Ventricle contraction causes the pressure in the ventricles to exceed the pressure in the aorta/ pulmonary artery, causing the semilunar valves to open.
Right ventricular contraction pushes atrioventricular valve into the atrium causing a ‘c’ wave.

Question 16

What happens during the reduced ejection phase of the cardiac cycle?

Answer 16

Ventricular pressure falls and blood flow decreases. Ventricular pressure less than aorta/ pulmonary artery pressure so blood begins to flow back, causing the semilunar valves to close.

Question 17

What happens during the isovolumetric relaxation stage of the cardiac cycle?

Answer 17

Ventricular pressure continues to fall and volume falls to minimum, ready to refill again with blood.

Question 18

What happens during the raid ventricular filling stage of the cardiac cycle?

Answer 18

Atria pressure exceeds ventricle pressure and the atrioventricular valves open. Ventricular volume increases rapidly as blood flows from atria.

Question 19

What happens during the reduced ventricular filling stage of the cardiac cycle?

Answer 19

Ventricular volume increases more slowly until nearly full

Question 20

What percentage of the ventricles are full at the start of atrial systole?

Answer 20

70-80% due to inflow during diastole

Question 21

What is the percentage contribution of the blood in the ventricles due to atrial contraction/ kick?

Answer 21

20-30%

Question 22

What is the pressure generated by the left ventricle greater than the pressure generated by the right ventricle?

Answer 22

Pressure generated by the left ventricle during ventricle systole (ie. rapid ejection) will be appreciably greater than the pressure generated by the right ventricle, as the blood needs to travel a greater distance from the pulmonary artery around the body. The volume of blood ejected will be the same, despite the differences in pressure, and this volume of blood is known as the stroke volume.

Question 23

What is stroke volume?

Answer 23

Volume of blood ejected by the ventricles each beat

Question 24

How is the heart supplied with oxygenated blood? How is deoxygenated blood removed from the heart?

Answer 24

The heart is supplied with oxygenated blood by the coronary arteries and deoxygenated blood is removed from the myocardium by coronary veins.

Question 25

What causes myocardial infarctions?

Answer 25

Myocardial infarctions are caused when there is a build up of plaque in the coronary arteries that repress the flow of blood to the heart cells. Macrophages ingest cholesterol and other lipids to form fatty streaks below the endothelial lining of coronary arteries, that eventually form a lipid core. Lipid core grows, with local smooth muscle cell division, to create a bulging plaque which develops hard calcified regions and fibrous collagen caps; if caps ruptures, it initiates a clot and causes a heart attack.

Question 26

What are heart muscle cells called?

Answer 26

Cardiomyocytes

Question 27

Describe the linkage of adjacent cardiomyocytes

Answer 27

The intercalated disc is a region where cardiomyocytes interlock and they contain desmosomes and gap junctionss. Desmosomes are anchors which prevent adjacent cells pulling apart during contractions. Gap junctions are ion permeable passages that allow stimulating impulses to move through cells.

Question 28

What are T-tubules?

Answer 28

Invagination of the sarcolemma that allow for the conduction of impulses to the deeper cell regions. T-tubules are only found at the Z discs.

Question 29

What is the sarcoplasmic reticulum?

Answer 29

Sarcoplasmic reticulum consists of a specialised SER that surrounds the myofibrils and stores calcium ions which are needed for muscle contractions.

Question 30

Describe the ‘sliding filament theory’

Answer 30

Cardiac myofibrils and contractile filaments (actin and myosin) slide past each other during contraction