The lining of your gut has a barrier that is made up of mucous membranes around your Gastrointestinal tract (GIT). The mucosal barrier protects us from infections and infestations- ideally when everything is working as it should at optimal levels. A healthy intestinal barrier is key to optimal digestion and gut immunity.
The role of the mucosal barrier acts as a guard- a filter as it allows for nutrition to go through the hepatic portal system for proper digestion and assimilation…. BUT it should not allow offensive particles, as toxins, immune complexes, pathogens and maldigested food particles, into general circulation.
The hepatic portal system is the venous system that returns blood from the digestive tract and spleen to the liver were the raw nutrients in the blood are processed before the blood returns to the heart. The portal venous system is in charge of directing blood from the parts of the GI tract to the liver. Substances absorbed in the small intestine travel first to the liver for processing before continuing to the heart.
Now let’s look at the amazing detailed structure and many layers to the mucosal barrier. It is really fascinating if you think about it…
The small intestine itself is about 18-21 feet and works to absorb about 90% of our digestion and absorption of food occurs- with the other 10% taking place in the stomach and large intestine. The main function of the small intestine is to absorb the nutrients and minerals from food.
Digestion starts north- eating in a PNS “rest and digest” nervous system, chewing our food, churning and mixing in the mouth then into the stomach.
The next phase of digestion is the chemical phase that requires enzymes, bile acids and more to break down the food material into a form that we can absorb and then assimilated into the body.
The small intestine, when not damaged, has the largest surface area, because of the villi you can see in the images. The individual epithelial cells have finger like projections called microvilli.
Microvilli are on the outer surface- one layer of the cell on the villi then the epithelium layer which has the enterocytes, enteroendocrine cells…, goblet cells, Paneth cells, stem cells and proliferate progenitor cells. Then we get into the Crypt of Lieberkühn – the glands then into the Lamina Propria (area inside the villi and underneath) where the blood vessels and (fat transporting) lacteals are found. Lastly, we have the submucosa and the musculature.
See the layers- of micro-villi and let’s focus on these finger-like projections (shag carpet) which make up our “brush border”. If the “shag carpet” gets damaged, then they become blunted and damaged – “Berber carpet” appearance.
The sensitive brush border micro-villi need to be healthy as they increase the surface area of the small intestinal wall which creates more space for nutrient absorption from the gut to occur. Also, these little villi produce enzymes to break down sugars and more nutrient absorption occurs in the enterocytes via diffusion as well as the microfilaments help in motility to the microvilli.
The intestinal absorptive cells transport molecules from the intestine into the hepatic portal system (liver) via diffusion where we see;
- Water uptake
- Sugar uptake
- Amino acid uptake
- Small fatty acids/lipid uptake
- Vitamin uptake
- Resorption of bile
- Secretion of SIgA from the plasma cells in the submucosa
Now head to PART TWO…