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."

Ischemia

Ischemia is any reduction in blood flow resulting in decreased oxygen and nutrient supplies to a tissue. Ischemia may be reversible, in which case the affected tissue will recover if blood flow is restored, or it may be irreversible, resulting in tissue death. Ischemia can also be acute, due to a sudden reduction in blood flow, or chronic, due to slowly decreasing blood flow. Ischemia can occur anywhere in the body. Heart attacks and strokes can both result from ischemia. Although less well known, ischemia can also affect the intestines, resulting in abdominal pain, bloody stool, and even intestinal rupture or gangrene. Peripheral ischemia can lead to loss of fingers or toes or the need for limb amputation.