Above in pink we see the small intestine. The first stop for nutrients after they go through the stomach.
The sophisticated internal walls of the small intestine are similar to our tongue, with micro folds or microvilli, which increase the surface that absorbs nutrients. If we stretched it out, it would cover the area of an entire tennis court! Nature has created a perfect system here, concentrating as much contact surface for nutrient absorption, in as little space as possible.
The small intestine walls filter beneficial nutrients allowing them to flow into the blood stream.
Next, comes the area in grey: the large intestine. The colonies of bacteria in the large intestine digest nutrients that have not been digested until that point. Mostly carbohydrates. Another function of the large intestine is to remove water from the nutrients, turn them into feces, and then eliminate it.
How important is it?
About 75% of the immune system is located in the gut, because the lymphatic tissue is, like a web, interlaced within our intestinal walls.
When elimination is not occurring, a serious consequence can be less acidic pH in the intestinal environment. Lack of acidity can weaken the immune system and make the whole body vulnerable to pathogens and free radicals. Malfunction in the large intestine will also be caused by:
- Unbalanced flora due to antibiotics.
- A diet poor in insoluble fibers.
- Decreased quantity and variety of carbohydrates in general.
All the above contributes to decreased fermentation, leaving the environment vulnerable to the attack of harmful bacteria.
Unbalanced gut flora, or microbiota, as we explain later, has immediate effects over the brain, the immune system and hormones.
Our gut microbiota has been primarily given to us by contact with our mother during birth and breastfeeding. There is evidence that the flora acquired during childhood will determine several aspects of our health, including protection against infections, susceptibility to obesity, and psycho-emotional conditions.
Many studies closely correlate an unbalanced flora to diabetes, and inflammatory brain processes such as autism, Alzheimers, Parkinson's and auto-immune diseases.
Besides that, around 80% of our serotonin is produced in the intestine. Serotonin is the neurotransmitter important for our mood, social behavior, appetite, digestion, sleep, memory and sexual desire.
Our Second Brain? Really?
Think of a web of interlaced threads that permeates the digestive tract, from the mouth to the anus. These threads are neurons and the web is called Enteric Nervous System. The ENS existed way before the origin of human race. Our species is about 2 million years old, while the Enteric circuits existed 500 million years ago, even within invertebrates! The ENS is way more ancient than the brain and is extremely sophisticated! The ENS communicates to the Central Nervous System through the vagus nerve, in yellow below: