heart

• The left ventricle has a thicker wall so it can withstand the high pressures and pump blood out of the aorta so oxygen can be recieved to all parts of the body.
• The pressure on the right side of the heart must be kept low to prevent the capillaries in the lungs from bursting.
• right side oxygenated blood
• left side deoxygenated blood

• vena cava carries the blood with very little oxygen from the body tissues
• right atrium
• tricuspid valve
• right ventricle
• pulmonary artery carries the blood to the lungs to collect oxygen
• lungs
• pulmonary veins carry oxygenated blood back to the heart
• left ventricle
• bicuspid valve
• left atrium
• aorta then carries the blood with a lot of oxygen to the body

Pulmonary artery
The pulmonary artery branches after leaving the right ventricle, each branch carrying deoygenated blood to one lung. It is the only artery that carries deoxygenated blood.

Inferior vena cava
Deoxygenated blood returns from the lower body and legs and enters the right atrium through the inferior vena cava.

Pulmonary veins
Newly oxygenated blood from the lungs returns to the left atrium via the four pulmonary veins; oxygenated blood is not carried in veins anywhere else in the body.

Superior vena cava
This large vein carries used blood from the head and arms into the right atrium.

Atrioventricular valves

• ventricle walls relax and recoil after contracting
• The pressure in the atria is higher than the ventricles causing the atrioventricular valves to open

• blood flows straight through the atria into the ventricles
• ventricles contract pressure of blood increases in the ventricles
• when the pressure of blood is higher in the atria than the ventricles blood moves up and valves snap shut
• this prevents back flow

• Ventricles contract when the pressure in the major arteries is higher than the pressure in the ventricles SEMILUNAR VALVES CLOSED.

• Pressure builds up in the ventricles as the semilunar valves - closed
• once the pressure in the ventricles is higher than the aorta and pulmonary artery the SEMI LUNAR VALVES OPEN and blood is pushed out in a high pressure

• elastic fibres in the ventricle walls recoil and go back into shape. pressure drops below the major arteries.
• As blood leaves the semilunar valves they shut so blood will not return to the ventricles

Filling phase

• Atrium and ventricle relax, internal volume increases and blood flows into the heart from the major veins.
• Blood flows into the atria through the open atrioventricular valves into the ventricles
• This cycle is called Diastole

Atrial contraction

• Atrium contracts small increase in pressure helps to push blood into the ventricles. This stretches the walls of the ventricles so they are full of blood
• contraction of atria is called Atrial Systole
• Blood fills the atrioventricular valve causing them to snap shut preventing backflow

Ventricular contraction

• Wall of the ventricle contracts - Ventricular systole
• contraction starts apex of the heart upwards towards the arteries
• Semi-lunar valves open and blood is pushed out of the heart.

• Cardiac muscle is MYOGENIC initates its own heart beat
• muscles contract and relax in sync
• FIBRILLATION are contractions which are not in a sychronised way in all four chambers

P- wave of excitation sweeping over the atria

QRS- wave of excitation in ventricalar walls

T- recovery of ventricle walls