Cardiac Cycle

Question 1

Diastole

Answer 1

Period of ventricular relaxation

Question 2

Systole

Answer 2

Period of ventricular contraction

Question 3

Normally diastole is

Answer 3

Longer than systole

Question 4

General principals of cardiac cycle

Answer 4

1) contraction of the myocardium generates pressure changes which result in the orderly movement of blood
2) blood flow from high to low pressure, unless flow is blocked by a valve
3) events on the right and left hand sides of the heart are the same, but pressures are lower on the right

Question 5

Sinoatrial node

Answer 5

• aka. the pacemaker
• small patch of tissue with its own inherent rhythm of contraction, the speed of which is controlled by nervous impulses and hormones
• determined the rate of contraction of the rest of the cardiac muscles
• generates cardiac impulses

Question 6

Cardiac impulses

Answer 6

Waves of electrical impulses

Question 7

Atrioventricular septum

Answer 7

• non-conductive connective tissue
• delays cardiac impulses when they reach the junction between the atria and the ventricles
• delay gives time for the wave of contraction to pass over the whole of both atria
• separates the atria from ventricles except for atrioventricular node

Question 8

Atrioventricular node

Answer 8

• the only route of transmission for the cardiac impulses
• acts as a second pacemaker region, relaying the cardiac impulses to the ventricles
• takes over as a pacemaker of the whole heart of the SA node malfunctions
• has a slower inherent rhythm

Question 9

Diastole détail

Answer 9

• blood enters the atrium through the pulmonary veins and the vena cava
• pressure rises until > pressure in ventricles
• atrioventricular valves open
• walls of both atria and ventricles are relaxed
• relaxing ventricular walls allows muscular wall recoil
• reduces pressure even further
• much lower than pulmonary artery and aorta
• closes the semi-lunar valves

Question 10

Atrial systole

Answer 10

• wave of electrical excitation spreads of the SAN across both atria, causing them to contract
• contraction for arterial walls and recoil of ventricular walls
• forces all remaining blood from atria to ventricles
• ventricle walls remain relaxed

Question 11

Ventricular systole

Answer 11

• wave doesn’t reach the ventricles due to atrioventricular septum
• wave reaches the atrioventricular node in the atrial walls
• short delay
• atrioventricular node converts wave of electrical excitation between the ventricles along the Purkyne fibres
• Bundle of His conducts the wave to the base of the ventricles
• wave released from purkyne fibres causes ventricle to simultaneously contract from the bottom of the heart upwards, increasing pressure
• atrioventricular valves forced shut; no backflow; lub
• pressure continues to rise until ventricular pressure > arterial pressure
• semi-lunar valves open and blood is pumped out of the ventricles to the desired destination

Question 12

Why is there a short delay between wave reaching atrioventricular node and going along the purkyne fibres in ventricular systole?

Answer 12

ensures all of the blood leaves atria and enters ventricles

Question 13

How is simultaneous contraction of ventricles ensured?

Answer 13

Thin purkyne fibres carry impulses more slowly near the atrioventricular node, supplying less distant parts of the ventricle