The Circulatory System & Heart
Single circulatory system
- the blood only passes throught he heart once
Double circulatory system
- the blood passses throught the heart twice for each circuit.
Open Circulatory System
- blood isn't inclosed in blood vessels all the time, it flows freely throught the body cavity.
Closed Circulatory System
- the heart pumps blood into arteries. these branch out into millions of capillaires.
Valves only open one way and are open and close depending on the relative pressure of the heart chambers. If there's a higher pressure behind the valve it will be forced open. .
- The atrioventricular Valves link the atriums to the ventricles.
- the semi-lunar valves link the ventricles to the pulmonary artery and aorta.
The Chambers of the heart are made up of muscle.
The left side is thicker as it has to pump blood all around the body.
The ventricles are also thicker as the atriums are only pumping a short distance rather than to the lungs/body.
The Cardiac Cycle
The cardiac cycle consists of ongoing relaxation and contractions in the hearts chambers. Blood enters the heart in the atriums, therefor the first contractions occur in the atria:
- the atria fill with blood - increasing the pressure
- the atria contract
- the high pressure causes the atrioventricular valves to open
- the blood flows into the ventricles.
- the ventricles contract
- the pressure decreases in the atria - atrioventricular valves shut and prevent back-flow
- the semi-lunar valves are forced open
- blood flows into the pulmonary artery and aorta.
- both the ventricles and aorta relax - their volume area increases.
- the cycle starts again! <3
sino-atrial node - atrioventricular node - bundle of his - purkyne tissue
he electrical impulses are what causes the hearts chambers to contract.
1) The process starts at the sino-atrial node. The node sends out waves of electrical activity to the atrial walls.
2) the waves cause the atria to contract but are stopped at the ventricles by non conducting collagen tissue.
3) Instead the impulse hits the atrioventricular node where there is a brief pause to make sure the atria contractions are complete.
4) The atrioventricular node passes the waves to the bundle of his (a bundle of muscles fibres) which conduct the waves to the finer muscle fibres.
5) The finer muscle fibres are called purkyne tissue which spread round the ventrical walls.
6) the waves cause the ventricular walls to contract simultaneously from the bottom up - to make sure no blood is left at the bottom.
- records the electrical activity of the heart.
Depolarise - lose electrical charge
Repolarise - gain electrical charge
An electocardiograph records as the heart depolarises and repolarises as this shows when it is contracting and relaxing by the electrodes placed on the chest.
- carry blood from the heart to the rest of the body
- walls are thick and muscular to withstand high pressure
- walls have elastic tissue
- inner endothelium (lining) is folded to allow expansion
- all carry oxygenated blood apart from the pulmonary arteries
Capillaries (the smallest blood vessels)
- arteries branch into capillaries
- glucose and oxygen are exchanged between glucose and oxygen
- adapted for efficient diffusion with walls only one cell thick
- take blood to the heart at low pressure
- wider than arteries with little elastic tissue
- contain valves to prevent back-flow
- blood flow is helped by contractions of the surrounding muscles
- all carry deoxygenated blood apart from the pulmonary veins.