Blood

"Blood is a constantly circulating fluid providing the body with nutrition, oxygen, and waste removal. Blood is mostly liquid, with numerous cells and proteins suspended in it, making blood ""thicker"" than pure water. The average person has about 5 liters (more than a gallon) of blood.
A liquid called plasma makes up about half of the content of blood. Plasma contains proteins that help blood to clot, transport substances through the blood, and perform other functions. Blood plasma also contains glucose and other dissolved nutrients.
About half of blood volume is composed of blood cells:
• Red blood cells, which carry oxygen to the tissues.
• White blood cells, which fight infections.
• Platelets, smaller cells that help blood to clot.
Blood is conducted through blood vessels (arteries and veins). Blood is prevented from clotting in the blood vessels by their smoothness, and the finely tuned balance of clotting factors."

Hypovolemia

Hypovolemic shock is an emergency condition in which severe blood and fluid loss make the heart unable to pump enough blood to the body. This type of shock can cause many organs to stop working. Losing about 1/5 or more of the normal amount of blood in your body causes hypovolemic shock.
Blood loss can be due to:
1. Bleeding from cuts
2. Bleeding from other injuries
3. Internal bleeding, such as in the gastrointestinal tract
The amount of circulating blood in your body may drop when you lose too many other body fluids, which can happen with:
1. Burns
2. Diarrhea
3. Excessive perspiration
4. Vomiting.