GCSE Revision Notes (t/b p 80 – 91, 283 – 295 )
Unit 8 BLOOD AND IMMUNITY
Functions of the circulatory system
- Transport – oxygen, carbon dioxide, digested food, urea.
- Protection – blood clotting, production of antibodies.
- Body temperature – this is maintained at 37 0C.
Structure of the blood
Red blood cells (erythrocytes) – no nucleus, biconcave discs, contain haemoglobin. This allows for the easy diffusion and transport of oxygen.
Oxygen collected at lungs
Oxygen released at cells
White blood cells (leucocytes)
Phagocytes - engulf and digest other dead cells, bacteria etc.
- irregular shape means they can squeeze through the capillary walls
- lobed nucleus.
Lymphocytes - produce antibodies
- large round nucleus.
Platelets - blood clotting. These tiny cell fragments release an enzyme that changes a blood protein fibrinogen into long threads of fibrin. These threads block the wound.
Plasma - this is the straw coloured liquid of the blood. It transports dissolved materials e.g carbon dioxide, glucose, urea, hormones etc.
Double circulation – the blood goes through the heart twice in one complete circuit of the body.
Pathway of blood through the heart –
· Deoxygenated blood in the vena cava flows from the body into the right atrium.
· The right atrium contracts and forces blood into the right ventricle through a valve.
· The right ventricle contracts and forces blood through a valve to the lungs in the pulmonary artery.
· The oxygenated blood returns from the lungs in the pulmonary vein and enters the left atrium.
· The left atrium contracts and forces blood into the left ventricle through a valve.
· The left ventricle contracts and forces blood through a valve into the aorta and then to the rest of the body.
Note : Valves ensure blood flows one way through
Note : left ventricle has thicker walls than right ventricle because it has to pump blood all round the body
Carry blood away from the heart
Carry blood to the heart
Connect arteries to veins in the organs of the body
Carries oxygenated blood
Carries deoxygenated blood
(exception- pulmonary vein)
Oxygen diffuses out to the cells
Carbon dioxide diffuses into the capillary
Valves to prevent backflow