Final answer:
Bruises are black or blue marks on the skin resulting from injury where blood vessels burst and leak, without breaking the skin. These are sometimes confused with petechiae, which are smaller red or purple spots from damaged vessels. As healing progresses, bruises change color as the body reabsorbs the leaked blood.
Step-by-step explanation:
Black or blue marks resulting from blunt force causing tiny underlying blood vessels to burst and leak into the skin but do not cause a break in the skin are known as bruises. These bruises occur when blood vessels are damaged due to injury and blood leaks into the surrounding tissue. This process can be compared to petechiae, which are small red or purple spots on the skin from blood leaking out of damaged vessels, but a bruise typically covers a larger area.
Bruises are a common type of injury wherein blood and blood components such as erythrocytes and white blood cells leak out of the breaks in the blood vessels. The discoloration seen in bruises is due to the body's natural healing process, where the leaked blood is broken down and reabsorbed by the body, usually changing color from black and blue to green and yellow as it heals.