The Heart

Question 1

What are the functions of the cardiovascular system ?

Answer 1

• distribution of nutrients
• support for metabolism (transportation of oxygen and carbon dioxide and metabolic waste products)
• distribution of water and electrolytes
• transportation and distribution of hormones

Question 2

What is the arrangement of the cardiovascular system ?

Answer 2

• the heart has 4 chambers and has a unidirectional flow of blood
• the blood in the systemic vascular beds runs in parallel
• the pulmonary circulation of blood runs in series

Question 3

What is the role of the valves ?

Answer 3

they prevent backflow of blood and ensure unidirectional flow

Question 4

Why is the muscle on the left side of the heart greater in volume than on the right side of the heart ?

Answer 4

The left ventricle contracts more powerfully in order to supply blood all around the body whereas the right side of the heart only supplies blood to the lungs

Question 5

What is the cardiac output at rest ?

Answer 5

~ 5 litres per minute

Question 6

What is the formula to calculate cardiac output ?

Answer 6

cardiac output = heart rate x stroke volume

Question 7

What is stroke volume ?

Answer 7

the amount of blood leaving the heart per beat (ml per beat)

Question 8

Where is the sinoatrial node located ?

Answer 8

in the right atrium

Question 9

What is the role of the sinoatrial node ?

Answer 9

• it is the natural pacemaker of the heart
• it generates the spontaneous rhythm of the heart by sending electrical impulses into the atrioventricular node and then down into the bundle of his and down to the septum where the impulses are then sent up the ventricles

Question 10

How does the SAN generate the spontaneous rhythm ?

Answer 10

The resting membrane potential of the SAN is not stable and is constantly depolarising
threshold is then reached and then repolarisation begins
the action potential generates the electrical impulses

Question 11

What does the ECG trace show ?

Answer 11

It represents electrical activity in the whole heart

Question 12

What does the P wave on the ECG show ?

Answer 12

depolarisation of the atria

Question 13

What does the QRS complex on the ECG show ?

Answer 13

depolarisation of the ventricles

Question 14

What does the T wave on the ECG show ?

Answer 14

repolarisation of ventricles (ventricles are relaxing and filling)

Question 15

What does the PR interval on the ECG complex show ?

Answer 15

it shows the speed of conduction from the atria to the ventricles through the atrioventricular node

Question 16

What does the QT duration on the ECG complex show ?

Answer 16

it shows the electrical activity taking place in the ventricles - depolarisation and repolarisation of the ventricles

Question 17

How can the heart rate be modified ?

Answer 17

• autonomic nervous system (sympathetic and parasympathetic)
• circulating hormones e.g. acetylcholine

Question 18

What does parasympathetic stimulation do to the heart rate ?

Answer 18

It decreases the frequency of action potentials and slows the heart rate

Question 19

What does sympathetic stimulation do to the heart rate ?

Answer 19

It increases the frequency of action potentials and increases the heart rate

Question 20

How does a cardiac ventricular action potential differ from a nerve action potential ?

Answer 20

The cardiac ventricular action potential incudes a plateau phase where the net movement of calcium ions out of the cell is equal to the inwards movement of potassium ions

Question 21

What is calcium-induced calcium release ?

Answer 21

It is when calcium ions move into a cell and cause calcium ions to be released from intracellular stores and this is important in EC coupling of cardiac myocytes

Question 22

How is contraction of the heart coordinated ?

Answer 22

• contraction is highly organised
• atrial contraction is followed by ventricular contraction
• relaxation is also coordinated to allow filling

Question 23

What is systole ?

Answer 23

contraction of chamber and ejection of blood

Question 24

What is diastole ?

Answer 24

relaxation and filling

Question 25

Briefly describe the cardiac cycle

Answer 25

1) Atrial systole
2) Isovolumic contraction of the ventricles
3) Ventricular ejection
4) Isovolumic relaxation of the ventricles
5) Passive ventricular filling

Question 26

What is isovolumic contraction ?

Answer 26

It is when the valves are closed so the volume is not changing but the pressure is increasing

Question 27

How can stroke volume be modified ?

Answer 27

• intrinsic control : degree of stretch of cardiac muscle - this is what returns to the heart from the venous end (Starling’s law)
• extrinsic control : sympathetic stimulation (modulation of calcium ion availability)