The circulatory system consists of the heart and the blood vessels (veins, arteries and capillaries).
Veins bring blood away from the heart. They have a wider lumen and thinner walls than arteries, and valves to prevent backflow of blood.
Arteries carry blood away from the heart. they have a narrow lumen, thick walls and no valves.
Capillaries are thin blood vessels(1 cell thick) that allow substances to pass into and out of the blood. They join veins to arteries.
Blood
Plasma is the liquid part of the blood .
Red blood cells are the most numerous blood cells. They are made in bone marrow and they contain haemoglobin to transport oxygen. They also give the blood its red colour.
Iron is needed to make red blod cells.
White blood cells fight disease.
Platelets clot the blood to stop bleeding.
Red blood cells have a biconcave shape and no nucleus.
The Heart
The heart is made of cardiac muscle – a type of muscle which never tires.
It contracts to pump blood around the body.
It consists of 4 chambers – right & left atriums, right & left ventricles.
The right side of the heart pumps deoxygenated blood to the lungs.
The left side of the heart pumps oxygenated blood to the rest of the body. The heart wall is therefore thicker/stronger on the left.
The heart has 2 valves to control the direction of the flow of blood.
Exercise and the rate of heartbeat
The normal heartbeat rate of a resting human is 70 beats per minute.
Exercise increases the heartbeat rate. This is because during exercise the cells need to produce more energy, so they require more food and oxygen.
The normal body temperature in the human body is 37°C.
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