What happens to blood as soon as it leaves the body?

Once blood leaves the body, it begins to undergo a series of changes. It cools down to ambient temperature, and without the body's mechanisms to maintain it, it starts to coagulate due to the activation of clotting factors. Cellular components may begin to break down, and bacteria can rapidly multiply if the blood is exposed to the environment. Ultimately, the blood can undergo decomposition, leading to further changes in its composition and appearance.