Overview of bleeding caused by abnormal blood vessels

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Bleeding may result from abnormalities in

Platelets
Coagulation factors
Blood vessels

Collagen is a protein that is important in maintaining strong blood vessels in the body. When collagen is abnormal or abnormal substances in the blood get into vessel walls, the vessels weaken and bleeding can develop.
Fragile blood vessels cause bleeding under the skin, leading to tiny red, purple or brown spots on the skin (petechiae), red or purple blemishes or bruises (purpura), and bruising. Most disorders caused by fragile blood vessels do not cause serious blood loss. The genetic disorder hereditary hemorrhagic telangiectasia is an exception.
Abnormalities of collagen in the blood vessels may occur in scurvy (due to lack of vitamin C in the diet) and in Ehlers-Danlos syndrome