The blood vessel is a natural regulator of normal haemostasis. It creates a physical barrier which prevents blood from mixing with proteins in the sub-endothelium which anchor platelets and trigger coagulation.

There are three layers in the blood vessel:

  • Tunica intima: this is a layer of endothelial cells. Endothelial cells express a variety of proteins which are integral to the regulation of normal haemostasis.
  • Tunica media: this is a layer of smooth muscle which varies in thickness depending on whether the blood vessel is an arterial or venous vessel, as well as its size. The smooth muscle layer is generally thicker in arteries.
  • Tunica adventitia: this is a layer of connective tissue which supports the structure of the blood vessel.