The structure/function of the human heart

• Blood enters atria 
• Walls of atria contract -> raises pressure of the blood in atria + forces open biscupid and tricuspid valves
• Blood passes through these valves + into ventricles
• When ventricles are full -> they contract -> increases the pressure of blood in ventricles which closes biscupid and triscupid valves again.
• Ventricles continue to contract + pressure continues to increase -> forces open semi-lunar valves at base of aorta + pulmonary artery
• Blood is ejected into these two arteries
• Pulmonary artery carries blood to the lungs + aorta has branches to carry blood to all other parts of body
• As ventricles empty, higher pressure in aorta + pulmonary artery closes valves in blood vessels and cycle restarts.

• Muscles release more energy -> in need of an increased supply of oxygen for aerobic respiration
• To deliver extra oxygen -> no. heart beats per min. and volume of blood pumped with each beat (aka. stroke volume) increase

• Arteries carry blood from the heart to organs of the body -> this blood has been pumped from ventricles + puts lots of pressure on walls of the arteries => must be able to 'give' under pressure
• Veins carry blood from organs back towards the heart -> this blood is lower than in the arteries => very little pressure on walls of veins
• Capillaries carry blood through organs + brings blood close to every cell in the organ. Substances are transferred between blood in capillary and cells => capillaries must be small enough to fit between cells + allow materials to pass through their walls easily.

Red

• Function: to transport oxygen => combines with haemoglobin to make oxyhaemoglobin (aka. red blood cell is 'loading' oxygen).
• As red blood cells pass through lungs, they load oxygen, as they pass through active tissues they unload oxygen.
• DON'T HAVE A NUCLEUS => allows more haemoglobin to be packed into blood cells

WHITE

• Function: to protect body against invasion by pathogens
• Do this in two ways: PHAGOCYSTS and ANTIBODY PRODUCTION
• PHAGOCYSTS: Phagocytes ingest microorganisms => change shape -> produce extensions of cytoplasm called PSEUDOPODIA 
• ANTIBODY PRODUCTION => production of antibodies that stick to the surgace antigens and destroy the pathogen