The Blood

Blood is made of four constituent parts - red blood cells, white blood cells, platelets and plasma. Each part plays a vital role in ensuring that blood can meet its two primary roles, to transport substances around our body and to defend against infection by potential pathogens.

Used to transport materials around the body and protect against disease 

Blood is a tissue which includes, liquid, cells, cell fragments and solutes.

Red Blood Cells 

Tiny, nucleus-free cells which carry oxygen from the lungs to tissues 

Oxygen transport is efficient because:

• there are huge numbers of red blood cells
• the cells are tiny so they can pass through narrow capillaries
• the cells have a flattened disc shape to increase surface area - allowing rapid diffusion of oxygen
• the cells contain haemoglobin - which transports oxygen and carbon dioxide around the body
• (Oxygen + haemoglobin = Oxyhaemaglobin (in oxygen rich places e.g. lungs) In low-oxygen environments (e.g. body cells) oxyhaemaglobin releases oxygen to become haemoglobin again. Bright red blood= oxygenated Dark red= deoxygen

White Blood Cells 

Different types of white blood cells exist. Some white blood cells can engulfbacteria and other pathogens by phagocytosis. They can change shape easily and produce enzymes which digest the pathogens.

Other types of white blood cell secrete antibodies and antitoxins to help destroy pathogens.

Blood Plasma 

Straw coloured liquid that makes up 55% of the blood. Transports dissolved substances around the body e.g. Hormones, antibodies, Nutrients (water, glucose, amino acids, minerals and vitamins), Water substances (carbon dioxide and urea)

Transports....

• Carbondioxide from the organs to the lungs 
• Soluble products of digestion from the small intestine to other organs 
• Urea from the liver to the kidneys 

Platelets

Platelets are small fragments of cells, but they do not possess a nucleus. They are involved in the process of forming clots at sites where there is a wound, eg a cut or graze