The Digestive System – Our Second Brain
Julia Wójcik
2026-03-16
7 min. read
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In recent years, our knowledge about the digestive system has significantly expanded. It turns out that its function is not limited to the digestion process alone. The digestive system and the bacteria residing in it are in constant exchange with the brain, which has a significant impact on human health, well-being, mental state, and behavior. Is this the same thing we refer to as the gut-brain axis? How does the digestive system influence the functioning of the brain?
Anatomical structure and segmentation of the intestinal tract within the human digestive system
The human intestinal tract is composed of two primary divisions: the small intestine and the large intestine. The former—the small intestine—comprises three distinct anatomical segments: the duodenum, which serves as the initial section directly connected to the stomach; the jejunum, characterized by its relatively empty, thin-walled structure; and the ileum, notable for its numerous coiled loops. Conversely, the large intestine is subdivided into the cecum, functioning as a reservoir for chyme; the colon, distinguished by its intricate anatomical configuration; and the rectum, representing the terminal portion of the digestive tract. The small intestine, averaging five to six meters in length in adults, plays a pivotal role in digestive processes—here, the enzymatic breakdown of nutrients continues with the aid of pancreatic secretions and bile, accompanied by extensive absorption of digested products into the bloodstream. Meanwhile, the large intestine, measuring approximately one and a half meters, is responsible for reabsorbing water from indigestible residues, consolidating fecal matter, and shaping it prior to excretion. Additionally, the lumen of the large intestine hosts a diverse gut microbiota, whose metabolic activities are essential for fermenting undigested dietary fibers and synthesizing certain vitamins.
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