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Two systems control the digestive process: the endocrine system and the nervous system. When the endocrine system senses changes in the body, it sends a chemical message in the form of hormones to tell the body how to respond. For example, back to the digestive journey of the strawberry: once you ingest it, the small intestine detects the number of carbohydrates entering your system and helps your pancreas stimulate an insulin response. The nervous system works to regulate the digestive system by using nerve impulses and releasing neurotransmitters. Some of the control originates from nervous and hormonal connections between the digestive system and the central nervous system.

Hormones. Hormones play key roles in the body; you have hormones that help neutralize stomach acid, hormones that help with muscle contractions of the GI tract, hormones that slow gastric emptying, hormones that are released hours after consuming a meal to suppress appetite, and so on. These hormones work together to orchestrate the digestive process. One of the more critical hormones is ghrelin (a.k.a. the hunger hormone), which is released in response to low food intake or fasting. Ghrelin stimulates the release of growth hormone and encourages appetite. Overall, this hormone is fundamental to the regulation of long-term energy balance (vital for athletes who want to lose fat or gain muscle) and is potentially essential for longevity.

The enteric nervous system, or second brain. In addition to having control systems, the GI tract, and more specifically the intestines, also has what’s called the second brain (the enteric nervous system). It shares many similarities with the brain, such as neurotransmitter activity, signaling molecules, and the number of neurons present, as well as the size and complexity of the system. Communication between the gut and the brain happens in both directions—from the brain to the gut, and from the gut to the brain. This means that your emotions and stress can affect what happens in your gut. Alternatively, what happens in the tissues of your gut can affect your brain.

KEY STATS ABOUT THE SECOND BRAIN

The second brain is wondrously complex. For example, the gut (the intestines) has as many neurons as the spinal cord. The second brain is also affected by your thoughts, feelings, and physical sensations. If you’ve ever had “butterflies” before a big competition or stress-induced heartburn or a sudden urge to use the bathroom before a big race or climb . . . this is how the enteric nervous system communicates. Here are some other important facts:

•The surface area of the intestines is approximately 100 times greater than the surface area of the skin.

•The gut has the largest population of microorganisms of all body surfaces.

•The gut contains two-thirds of our immune system cells and also has thousands of hormone-producing cells, making it the largest endocrine organ.

•The gut uses and locally secretes neurotransmitters to help with digestion, such as GABA, norepinephrine, serotonin, and acetylcholine. It uses most of the body’s serotonin, dopamine, and melatonin.