The brain is finite
The brain is the final organ in most animals, since it does not have a separate digestive system: all nutrients and vitamins entering the bloodstream are completely absorbed and absorbed by brain tissue. The active substance of brain metabolism, glucose and other liquid components (electrolytes), is found in the blood and is formed in the liver as a result of the breakdown of food. Absorption of some fat-soluble vitamins and alcohol occurs from the lung tissues. The brain receives more than half of its nitrogen from the amino acid creatine, which breaks down into glycerol and ammonia in the muscles. Urea, formed in the neurons of the brain and released from the blood through the kidneys, is partially returned to the brain. Reabsorption of the product of the physiological activity of the brain ensures its connection with the anabolism of body tissues.