The enteric nervous system (ENS) has 100 million neurons (more than the spinal cord). The surface area of the GI tract is larger than the surface area of the skin. There must be this tremendous amount of surface area in order to exchange the nutrients and wastes as food and water transit the GI tract.
THE AUTONOMIC SYSTEM
The autonomic nervous system could be renamed the ‘automatic’ nervous system.
Our body sweats primarily as a means of thermoregulation. As the class of amphibians evolved, these creatures had to develop a new way of maintaining control over their core body temperature.