7.5: The Cardiac Cycle Flashcards
How many times does the cardiac cycle complete per minute
70
Three phases of the Cardiac Cycle
Diastole - Relaxation of the entire heart
Atrial systole - Contraction of the Atrium
Ventricular systole - Contract of the Ventricle
Meanings of diastole and systole
Diastole = Relaxtion
Systole = Contraction
Process of Diastole (Relaxation of the Heart)
Blood returns to the atria through the pulmonary vein and the vena cava.
As the atria fill, the pressure in them rises. When atrial pressure exceeds that of the ventricles, the atrioventricular valves open allow the blood to flow into the ventricles
Both the atria and the ventricles are relaxed at this point. The relaxation of the ventricle walls cause them to recoil and reduce pressure within.
This causes pressure to be lower than in the aorta and the pulmonary artery and so the semi-lunar valves close
Process of Atrial Systole
The contraction of the atrial walls, along with the recoil of the relaxed ventricle walls, forces the remaining blood into the ventricles from the atria
Throughout this stage the muscle of the ventricle walls remains relaxed
Process of Ventricular Systole
After a short delay to allow the ventricles to fill with blood, they contract simultaneously. This increases the blood pressure within them, forcing shut the atrioventricular valves and preventing back-flow of blood into the atria.
With the closed atrioventricular valves, the pressure of in the ventricles rises further. Once it exceeds that in the aorta and the pulmonary artery, blood is forced from the ventricles into these vessels.
The ventricles have thick muscular walls meaning they pump blood forcefully. The left ventricle wall is thicker than the right because it has to pump to the extremities.
Valves in the control of Blood Flow
Blood will always move from a region of higher pressure to one of lower pressure.
Valves are used to prevent any unwanted backflow of blood
Examples of valves
Atrioventricular valves - between the atrium and the ventricle. Prevent the backflow of blood when ventricular pressure exceeds atrial pressure
Semi-Lunar valves - in the aorta and pulmonary artery. Prevent the backflow of blood into the ventricles when the pressure in these vessels exceed that of the ventricles
Pocket vales - in veins. Prevents the backflow of blood into the veins away from the heart. Ensures blood goes towards the heart.
Design of valves
Made up of a number of flaps of tough, flexible and fibrous tissue.
When pressure is greater on the convex side of these cusps, rather than on the concave side, they move apart to allow blood to flow through these cusps.
Mammals system
Mammals have a closed circulatory system in which blood is confined to vessels, allowing the pressure within them to be maintained.
Cardiac Output
Cardiac output (dm^3/min) = heart rate (bpm) x Stroke volume (dm^3)
Chamber with the highest pressure
The ventricles have the highest pressure.
Summary of diastole
- Blood enters the atria and ventricles from the pulmonary artery/vena cava
- Semi-lunar valves closed
- Left and right atrioventricular valves open
- Relaxtion of ventricles allows blood to enter from atria
Atria are relaxed and fill with blood, so are the ventricles
Summary of Atrial Systole
- Atria contract, pushing blood into the ventricles. Ventricles remain relaxed
- Semi-lunar valves closed
- Left and right atrioventricular valves open
- blood pumped from atria to ventricles
Summary of Ventricular Systole
- Atria relax, ventricles contract, pushing blood away from the heart through pulmonary arteries and the aorta.
- Semi-Lunar valves open
- Left and right atrioventricular valves closed
- Ventricles contract and walls thicken
