In mammals the blood contains

• plasma
• red blood cells
• white blood cells.

It transports

• nutrients
• oxygen
• carbon dioxide.

Red blood cells are specialised by

• being biconcave in shape
• having no nucleus
• containing haemoglobin.

This allows them to transport oxygen efficiently in the form of oxyhaemoglobin.

White blood cells

Pathogens are disease-causing micro-organisms (bacteria, viruses, fungi).

White blood cells are part of the immune system and are involved in destroying pathogens.

There are two main types of cells involved:

• Phagocytes carry out phagocytosis by engulfing and digesting pathogens.
• Some lymphocytes produce antibodies which destroy pathogens.
• Each antibody is specific to a particular pathogen.

The heart

The pathway of oxygenated (with oxygen) and deoxygenated (without oxygen) blood through heart, lungs and body is shown.

The heart has 4 chambers –

• Right Atrium (top left)
• Left Atrium (top right)
• Right Ventricle (bottom left)
• Left Ventricle (bottom right)

The heart also has 4 valves.

The heart has 5 associated blood vessels –

• aorta (takes oxygenated blood to the body cells)
• vena cava (returns deoxygenated blood to the heart)
• pulmonary artery (takes deoxygenated blood to the lungs)
• pulmonary vein (takes oxygenated blood to the heart from the lungs)
• coronary arteries (supplies oxygenated blood to the heart muscle cells)

Blood vessels

Arteries have thick, muscular walls, a narrow central channel and carry blood under high pressure away from the heart.

Veins have thinner walls, a wider channel and carry blood under low pressure back towards the heart.

Veins contain valves to prevent backflow of blood.

Capillaries are thin walled and have a large surface area, forming networks at tissues and organs to allow efficient exchange of materials.

Large capillary networks are found in the lungs, small intestine and the muscles, where efficient diffusion of materials into and out of cells is essential.

Topic Summary