The cardiovascular system is comprised of the heart and the network of arteries, veins, and capillaries that carries blood throughout the body. The average adult male has between 5-6 liters of blood while the average adult female has 4-5 liters. Blood transports oxygen and essential nutrients to all of the living cells in the body, and also carries waste products from the tissues to the systems of the body through which they are removed.

Extreme Preemies May Be at Risk for High Blood Pressure as Adults

In one study, researchers found that the risk for high blood pressure was tied to smaller-than-normal kidneys at birth. A second study by the same researchers found a link between high blood pressure and impaired function in the cells that line blood vessels.

Thanks to modern medicine, more very preterm infants have survived in the past 30 years than before, she said. But since these preemies are only now reaching their 30s and 40s, any potential health problems that may emerge as they reach their 60s and 70s aren't yet known,