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Blood clotting

If the skin is cut, the wound must be closed to prevent blood loss and the entry of pathogens. The formation of a scab does just that.

Blood contains tiny fragments of cells called platelets. These platelets are involved in blood clotting and scab forming.

Forming a scab

When skin is wounded, platelets are able to:

• release chemicals that cause soluble proteins to form a mesh of insoluble fibres across the wound
• stick together to form clumps that get stuck in the mesh

Red blood cells also get stuck in the mesh, forming a clot. This develops into a scab, which protects the wound as it heals.

Plasma

Plasma is a straw–coloured liquid that makes up just over half the volume of blood. The plasma has many functions:

• transports carbon dioxide from respiring cells to the lungs
• transports digested food from the small intestine to respiring cells
• transports urea from the liver to the kidneys for excretion
• distributes heat all around the body
• transports hormones from the glands where they are made to the target organs