The heart

Question 1

what are the stages of the cardiac cycle

Answer 1

1) atrial systole
2) ventricular systole
3) diastole

Question 2

outline the process of atrial systole

Answer 2

1) the atria walls contract increasing pressure and decreasing volume
2) the increase of pressure forces blood through the atrioventricular vales (bicuspid and tricuspid valves) into the ventricles

Question 3

outline the process of ventricular systole

Answer 3

1) the ventricle walls contract increasing pressure and decreasing volume
2) this forces blood up through the semi-lunar valves and out the heart into the pulmonary artery and aorta
3) blood cant flow back into the atria as the bi/tricuspid valves are shut from the rise in ventricular pressure

Question 4

what is the difference between the pulmonary artery and the aorta

Answer 4

P= carries deoxygenated blood to the lungs 
A= carries oxygenated blood to the body

Question 5

outline diastole

Answer 5

1) the ventricles relax increasing volume and decreasing pressure
2) the atria relax so blood from the vena cava and pulmonary vein enters and the cycle starts again

Question 6

explain why the atria and ventricles have different thicknesses of muscles

Answer 6

1) atria are thinner as they only need to pump blood to the ventricles so need lower pressures
2) ventricles are thicker ( left thicker than right) as they need to pump blood all around the body

Question 7

what is the function of valves

Answer 7

• prevents the backflow of blood

Question 8

what are the atrio-ventricular valves and when do they open and close

Answer 8

• the bicuspid and tricuspid valves in the atria
• close during ventricles contract during ventricle systole
• open when atria contract during atrial systole

Question 9

what are the semi-lunar valves and when do they open and close

Answer 9

• found at the base of the aorta and pulmonary artery
• open during ventricular systole
• close during diastole and atrial systole

Question 10

draw a graph representing changes in pressure of the heart

Question 11

what is the sino-atrial node

Answer 11

a cluster if specialised cardiac cells that acts as a pacemaker found in the right atrium which initiated a wave of excitation across the atria causing contraction

Question 12

what is the atrio-ventricular node

Answer 12

a specialised cluster of cardiac cells found in the centre of the heart which introduces a delay in the wave of excitation allowing atrial systole to complete

Question 13

explain the process of control of the heartbeat

Answer 13

1) a wave of excitation is initiated by the sino-atrial node causing atria to contract during atrial systole
2) the ventricles are insulated from the atria by a layer of connective tissue so the wave cant pass between the two
3) The atrioventricular node delays the wave allowing the atria to finish contracting before the contraction of the ventricles
4) The AVN passes the wave down to the bundle of His at the apex of the heart which is highly conductive and this passes the wave to the purkinje fibres in the ventricle walls
5) the impulse causes the contraction of the ventricles from the apex upwards pushing blood up the aorta

Question 14

what is an electrocardiogram

Answer 14

• ECG is a trace of the voltage produced by the heart detected by electrodes on the skin

Question 15

draw and label and ECG

Question 16

what is a P, QRS and T wave

Answer 16

P- voltage generated by the SAN showing the contraction of the atria (atrial systole)
QRS- shows the depolarisation and contraction of the ventricles (ventricular systole)
T- shows the repolarisation and ventricles (diastole)

Question 17

what causes pressure drops in the blood

Answer 17

1) friction between blood vessel walls and large surface area cause a drop in pressure in the arterioles
2) extensive capillary beds further reduce pressure as fluid leaks from capillaries to the tissues
3) The further from the heart the lower the pressure

Question 18

how is blood returned to the heart by veins

Answer 18

1) veins arent subject to pressure changes so their pressure is low
2) they have a large diameter lumen so blood flows faster despite low pressure
3) blood return is enhanced by the massaging effect of muscles around the veins