Circulatory System

• The blood flows into the two atria from the vena cava and pulmonary vein
• The atria contract, pushing the blood into the ventricles
• The ventricles contract, forcing the blood into the pulmonary artery and the aorta and out of the heart
• The blood then flows to the organs through arteries and returns through the veins
• The coronary arteries branch off the aorta and surround the heart to supply the heart with oxygenated blood

The arteries carry blood away from the heart

• The walls are strong and elastic so they can carry the blood at high pressure
• They have a thick layer of muscle to make them strong
• The elastic fibres allow them to stretch and spring back
• They have a small hole in the middle called the Lumen

The capillaries are involved in the exchange of materials at the tissues

• They are very small
• They carry blood really close to every cell in the body to exchange substances with them
• They have permeable walls, so substances can diffuse in and out
• They supply food and oxygen and take away the waste like carbon dioxide
• Their walls are only one cell thick, which decreases the distance which diffusion occurs
• Has a very small lumen

Veins carry blood to the heart

• The capillaries join up to form veins
• The blood is carried at low pressure so the walls aren't as thick
• They have a bigger lumen to help blood flow
• They have valves to help keep the blood flowing in the right direction

To calculate the rate of blood flow use

Rate of blood flow = volume of blood / number of minutes

The red blood cells carry oxygen from the lungs to the body

• They have a biconcave shape so they have a large surface area to absorb oxygen
• They don't have a nucleus so they have more space for oxygen
• They contain haemoglobin which binds to the oxygen to form oxyhaemoglobin
• In tissues, the oxyhaemoglobin splits up into haemoglobin and oxygen to release oxygen into the cells

The white blood cells defend the body against infection

• Some can change shape and engulf unwanted microorganisms - phagocytosis
• Others produce antibodies to destroy microorganisms
• Some produce antitoxins which neutralise the toxins released by microorganisms
• White blood cells do have a nucleus

The platelets cause blood clots

• They form blood clots to clot a wound
• This stops microorganisms getting into the body and it stops the blood pouring out
• A lack of platelets causes excessive bleeding and bruises

Plasma is the liquid that carries everything in the blood

• They carry nutrients like glucose and amino acids, the soluble products from digestion which are absorbed by the gut and taken to the body cells
• They carry waste products like carbon dioxide and urea so they can be removed from the body
• They carry antibodies and antitoxins that are released by the white blood cells
• They also carry hormones and proteins