Glycolysis in the erythrocyte is the most prominent pathway in the energy metabolism of blood. Blood cells constitute nearly half the volume of blood, and erythrocytes constitute more than 99% of blood cells. Mammalian erythrocytes contain no mitochondria and depend exclusively upon anaerobic glycolysis to meet their energy needs.

Blood also plays a role in transporting compounds metabolized in other tissues as follows:

1. Blood transports waste products/fuels. The bloodstream transports what may be one organ's waste product but another organ's fuel (for example, lactate from muscle to liver).

2. Blood transports oxygen from lungs to tissues, enabling exergonic oxidative pathways to occur, followed by transport of the resultant CO2 back to the lungs for exhalation.

3. The lipoprotein components of blood plasma play indispensable roles in transporting lipids.

4. Blood is also the medium of transport of hormonal signals from one tissue to another, and of exit for metabolic end products, such as urea, via the kidneys.