Biology: Transport in Humans

Unicellular organisms can use diffusion for movement of substances (LARGE SA:V)

Multicellular have to have transport systems because they have a LOW SA:V

Arteries: Carry blood away from the heart (always oxygenated apart from the pulmonary artery which goes to the lungs) Have thick muscular walls Have small passageways for blood (internal lumen) Contain blood under high pressure Veins: Carry blood to the heart (always de-oxygenated apart from the pulmonary vein which goes from the lungs to the heart) Have thin walls Have larger internal lumen Contain blood under low pressure Have valves to prevent blood flowing backwards Capillaries: Found in the muscles and lungs Microscopic – one cell thick Very low blood pressure Where gas exchange takes place. Oxygen passes through the capillary wall and into the tissues, carbon dioxide passes from the tissues into the blood

Blood has four key components:

Plasma

• Fluid part of blood
• Carries carbon dioxide, hormones and waste

Red blood cells

• Contain haemoglobin which carries oxygen
• Made in the bone marrow. The more you train the more red blood cells are made.

White blood cells

• An important part of the immune system, they produce antibodies and destroy harmful microorganisms
• Made in the bone marrow