6a: Heart and Blood Vessels

• Pulmonary circulation is when the right side of the heart sends deoxygenated blood from the body along the pulmonary artery to the lungs.
• Systematic circulation is when the pump on the left side sends oxygenated blood from the lungs along the aorta to the rest of the body.
• It is an advantage for the human heart to have two separate pumps rather than one because the right hand side generates pressure to send blood through the lungs where pressure drops. When it is returned to the left hand side it has more pressure so the blood can travel around the body at a fast enough rate to generate high metabolic rate.
• During diastole, the heart muscles relaxes during which time the atria again with blood from the vena cava and pulmonary veins.
• During diastole the semi lunar valves are closed because pressure is higher in arteries than in ventricles.
• In atrial systole blood fills the atria from the vena cava and pulmonary vein. The atrial muscle contracts, increasing the pressure above that of the ventricles. This forces the atrioventricular valves to open and blood flows into ventricles.
• In ventricular systole the ventricle muscles contract. The volume of the ventricle decreases, increasing the pressure. This causes the atrioventricular valves to close. The blood is pushed upwards, towards the arteries at the top of the heart. The semi lunar valves open and the blood flows into the aorta and pulmonary artery.
• The atrioventricular valves close when the pressure in the ventricle is greater than in the atria.
• The semi lunar valves open when the pressure in the ventricle is greater than pressure in arteries.