the heart

Question 1

explain the mammalian heart

Answer 1

• its a pump for both the pulmonary and systemic circulatory systems
• double pump working synchronously
• keeps oxygenated and deoxygenated blood separate
• the cardiac muscles are myogenic and never get tired

Question 2

what is the pressure in the atria

Answer 2

• they have thin muscle walls which only exert a small pressure
• only has to push the blood into the ventricles

Question 3

what is the pressure in the right ventricle

Answer 3

• it has higher pressure than the atria
• it has to push blood to the lungs so the muscle wall is thicker

Question 4

what is the pressure in the left ventricle

Answer 4

• it has the highest pressure
• it has to push the blood to the whole body meaning the muscle wall is up to 3 times as thick as the right ventricle

Question 5

what is the role of the septum

Answer 5

• stops oxygenated blood and deoxygenated blood from mixing
• ensures all of the deoxygenated blood geos to the lungs and the oxygenated blood goes to the body
• allows different pressures to be maintained on each side

Question 6

what are the different parts of the heart

Answer 6

• pulmonary vein
• left atrium
• atrioventricular valve
• left ventricle
• aortic valve
• aorta
  . septum
• pulmonary artery
• pulmonary valve
• right ventricle
• atrioventricular valve
• right atrium
• vena cava

Question 7

how do the valves open

Answer 7

• the valves open when the pressure is high
• the atrioventricular valve opens when the pressure in the atrium is greater than the ventricle
• the semilunar valves open when the pressure is greater in the ventricle than in the aorta/pulmonary artery

Question 8

how do the valves close

Answer 8

• the valves close to prevent the backflow of blood
• the blood will flow back to the atria which forces the valves shut
• the lub-dub sound the heart makes is due to the closing of the atrioventricular valves, followed by the closing of the semilunar valves

Question 9

explain the cardiac cycle

Answer 9

• the blood enters the atria from the vena cava and pulmonary vein, the atrioventricular valves open
• the atria contracts, the volume decreases and the pressure increases, causing the blood to enter the ventricle down the concentration gradient
• the blood enters the ventricles through the atrioventricular valves
• the ventricles contracts, causing the pressure to increase and the volume to decrease
• the blood is forces through the open semilunar valves into the aorta or pulmonary artery

Question 10

how is the cardiac cycle controlled

Answer 10

• the heart muscles are myogenic meaning they can control themselves
• the sinoatrial node is the hearts natural pacemaker and is located in the top right atrium

Question 11

explain the steps in the control of the cardiac cycle

Answer 11

• the SAN initiates a wave of excitation
• this spreads over the walls of the atria causing atrium systole
• it is prevented from going straight to the ventricles because of a layer of non conducting tissue
• the wave of excitation reaches the AVN, which delays the wave to allow the atria to fully contract
• the wave of excitation travels through the conductive tissue in the septum
• when it reaches the base of the ventricles, it travels up the purkinje fibres up the side of the ventricle, causing ventricular systole
• the heart then goes into a period of relaxation called diastole as the electrical signal is terminated