Lymph eventually drains into veins, and is mixed with blood for recirculation. Adequate fluid intake is crucial to maintain blood health. Cardiovascular fitness ensures good circulation. The blood system is very sensitive to malnutrition. If microorganisms or unwanted substances penetrate the physical barrier, the blood and lymph system presents the second line of defense.
Malnutrition lowers the bodies defense against invasive disease.
The Hormonal and Nervous System 78 Blood also carries chemical messengers, called hormones , to tissue sites around the body. Hormones act as messengers to initiate a response to a change in conditions. Hormones regulate hunger and affect appetite. They perform numerous functions in the body including regulation of digestive juices, menstruation in women, the body's reaction to stress, and many others. Hormones are secreted and released by glands .