The Heart

• The right atrium receives deoxygenated blood from the rest of the body through the vena cava.
• The blood then moves down into the right ventricle.
• The right ventricle pumps the blood up through the pulmonary artery and out of the heart, towards the lungs.
• The left atrium receives oxygenated blood from the lungs through the pulmonary vein.
• The blood then moves through to the left ventricle from the left atrium
• The left ventricle has thicker walls than the right ventricle as it then has to pump the blood out of the aorta to go to the whole of the body, whereas, the right ventricle only had to pump the blood up to the lungs.
• This also means that the blood in the left ventricle is under higher pressure than the blood in the right ventricle

When you exercise, your muscles need more energy so you respire more

You need to get more oxygen into your blood and remove CO2. For this to happen, your blood needs to flow faster, so your heart rate increases. Here’s how:

• High levels of CO2 are built up whilst you are exercising which is very dangerous
• These high levels are detected by receptors in the aorta and the carotid artery (an artery in the neck)
• These receptors send signals to the brain which then sends more signals to the heart, causing it to beat more frequently and with more force to get the CO2 out of the body.

• When an organism is threatened, its adrenal glands release the hormone adrenaline
• The adrenaline binds to specific receptors in the heart, causing the cardiac muscles to contract more frequently and with more force. This increases the heart rate so the heart pumps more blood.
• This increases oxygen supply to the tissues, getting the body ready for action