KA6 The structure and function of the heart Flashcards
What happens in the right side of the heart?
Deoxygenated blood enters the right atrium through the vena cava. It is pushed through the atrioventricular valve into the right ventricle. When the right ventricle contracts blood is forced out through a semilunar valve into the pulmonary artery which carries blood to the lungs where it releases CO2 and picks up O2.
What happens in the left side of the heart?
Oxygenated blood returns to the left atrium through the pulmonary vein. Contraction of the left atrium pushes the blood through the atrioventricular valve into the left ventricle. When the left ventricle contracts blood is forced out of the heart through a semi-lunar valve into the aorta. The aorta is the main artery of the body and it carries oxygenated blood to all body organs.
What is cardio output and how is it calculated?
CO= volume of blood pumped through each ventricle per minute.
Heart rate= number of heartbeats per minute
Stroke volume= volume of blood pumped through each ventricle per heartbeat
CO= HR x SV
What is the cardiac cycle?
The cardiac cycle describes the contraction and relaxation of the heart during one complete heartbeat. A resting heart beats on average 75 times per minute so each cardiac cycle lasts 0.8 seconds.
What are the 3 stages of the cardiac cycle?
1- Atrial systole (0.1s.)
2- Ventricular systole (0.3s)
3- Diastole (0.4s)
What happens in atrial systole?
During atrial systole the atria contracts pushing blood through the AV valves into the ventricles. The AV valves are open and the SL valves are closed.
What happens during ventricular systole?
The AV valves close causing the “lubb” sound of the heartbeat. The ventricles contract causing blood to be forced through the SL valves and into the pulmonary artery/ aorta.
What happens during diastole?
The high pressure in the arteries causes the SL valves to close. During diastole, blood returning to the atria flows into the ventricles.
What is responsible for the sound of the heartbeat?
The opening and closing of the AV and SL valves are responsible for the heart sounds heard with a stethoscope.
Where does the heartbeat originate?
In the heart itself.
What is the heartbeat controlled by?
The auto-rhythmic cells of the sino-atrial node (SAN) located in the wall of the right atrium set the rate at which the heart contracts.
How does the SAN work?
The timing of cardiac muscle cell contraction is controlled by impulses from the SAN spreading through the atria causing it to contract (systole)
How does the atrioventricular node (AVN) work?
Impulses from SAN travel to the AVN located in the centre of the heart. Impulses from the AVN travel down fibres in the central wall of the heart and then up through the walls of the ventricles, causing them to contract (systole)
What is an electrocardiogram? ECG
Impulses in the heart generate currents that can be detected by an ECG.
When does blood pressure increase and decrease?
Blood pressure increases during ventricular systole and decreases during diastole.
