The brain keeps the body healthy primarily by maintaining homeostasis. The brain works as a "base" for signals and information that is transmitted to the body. In keeping the body healthy, or in other words, maintaining homeostasis; there are sensory receptors in our body that bring afferent impulses towards the brain. The brain will then respond and send impulses towards the organ responsible for homeostasis.
For instance, in a person with a sudden drop of blood pressure, the carotid and aortic bodies (sensory receptors that sense the blood pressure) wherein this information is sent to the brain, specifically, the medulla. The brain will then respond by sending signals promoting vasoconstriction therefore increasing blood pressure back to normal. This cycle will end through negative feedback.
