Water makes up about 73 percent of the human brain and helps make hormones and neurotransmitters. The human heart also is composed of about the same percentage of water. The mature human body overall has a water composition of about 60 percent.
The human brain has an average mass of roughly three pounds, largely consisting of fat and protein and about 100 billion nerve cells. The cerebrum is the largest section of the brain, followed by the cerebellum. The cerebrum makes up 85 percent of the total mass and has two hemispheres. Each hemisphere is divided into four lobes, the frontal, parietal, occipital and temporal, each governing certain functions of the body.