Blood and Organs

Blood has four main components. Plasma, Platelets, Red blood cells and White blood cells.

Plasma

- Pale yellow liquid which carries everything that needs transporting around the body. It carries:
- Red and white blood cells and platelets
- Digested food products (like glucose ad amino acids) from the gut to all the body cells
- Carbon dioxide from the body cells to the lungs
- Urea from the liver to the kidneys
- Hormones, which act as chemical messengers
- Heat energy

Platelets

- When you damage a blood vessel, platelets clump together to 'plug' the area
- This is known as blood clotting. They stop you losing too much blood and prevent microorganisms from entering
- Platelets are held together by a mesh of protein called fibrin 

Phagocytes ingest Pathogens

• Phagocytes detect things that are foreign to the body. e.g pathogens. They engulf and digest them.
• They are non-specific and attack anything thats not meant to be there.

Lymphocytes produce Antibodies

• When there are foreign antigens (pathogens), white blood cells will start to produce proteins called antibodies and are specific to destroy that unique antigen. They then produce rapidly to fight all similar pathogens
• Some lymphocytes stay around the body as memory cells after the original infection has been fought off.
• Thats why you are immune to most diseases if you have already had them.

Arteries Carry Blood Under Pressure

• The heart pumps the blood out at a high pressure so the artery walls are strong and elastic
• The walls are thick compared to the size of the hole down the middle (lumen)
• The largest artery in the body is the aorta

Veins Take Blood Back To The Heart

• Capillaries eventually join up to form veins
• The blood is at a lower pressure in the veins, so the walls dont need to be as thick as artery walls
• They have a bigger lumen than arteries to help blood flow despite the lower pressure
• Valves to keep the blood flowing in the right direction
• The largest vein is called then vena cava.

Capillaries Are Really Small

• Arteries branch into capillaries. Capillaries are tiny, too small to even see. 
• 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 and are one cell thick
• They supply food and oxygen, and take away wastes like CO2

• The right atrium of the heart recieved deoxygenated blood from the body (through the vena cava)
• The deoxygenated blood moves through to the right ventricle, which pumps it to the lungs (via the pulmonary artery)
• The left atrium recieves oxygenated blood from the lungs (through the pulmonary vein)
• They oxygenated blood moves through the left ventricle, which pumps it out round the body
• The left ventricle has a thicker wall than the right ventricle because it needs more muscle because it has to pump blood round the WHOLE BODY rather then the right which is JUST THE LUNGS. 
• The blood in the left ventricle is under a higher pressure than the blood in the right ventricle 
• The valves prevent backflow

Exercise Increases Heart Rate

• When you exercise, your muscles need more energy, so you respire more
• You need to get more oxygen into the cells and remove more carbon dioxide. For this to happen, your heart rate increases.
• Exercise increases the amount of carbon dioxide in the blood
• High levels of blood CO2 are detected by receptors in the aorta and carotid artery 
• These receptors send signals to the brain
• The brain sends signals to the heart, causing it to contract more frequently and with more force.

The Hormonal System also helps Control Heart Rate

• When an organism is threatened (e.g. by a predator) the adrenal glands release adrenaline
• Adrenaline binds to specific receptors in the heart. This causes the cardiac muscle to contract more frequently with more force 
• This increases oxygen supply to the tissues