1. The intestine and its functions
2. Small intestine
3. Large intestine
4. Common gastrointestinal disorders
The intestine and its functions
The intestine is the portion of the digestive system that begins after the stomach which uses gastric juices to transform food into chyme.
It is chyme that enters the small intestine.
The main function of the intestines is to extract the nutrients from the food (chyme) ingested, absorb them and send them into the bloodstream so that they can be distributed throughout the body.
The intestine measures , approximately 7 metres, the length of which varies according to age, sex (in women it is slightly shorter) and individual conditions.
The gastrointestinal wall has several distinct layers:
– the mucosa covers the intestinal lumen and contains a layer of cells called enterocytes, whose role is to absorb nutrients;
– the submucosa, a layer below the connective tissue, contains many nerves, blood vessels and immune system cells;–
– the muscular layer is comprised of the muscles responsible for intestinal motility.
–the serosa, lthe outermost layer, made up of connective tissue that has a structural role
The intestinal lumen contains partially digested chyme plus populations of approximately 200 thousand billion microorganisms that form the intestinal microbiota.. These microbial communities, which perform metabolic and nutritional activities, have protective functions and boost the immune response against resident pathogens or those arriving from outside.
Anatomically, the intestine is separated intothe small intestineand the large intestine.
The small intestine starts with the pyloric sphincter, which separates it from the stomach, and ends with the ileocaecal valve, which connects it to the large intestine. It is approximately 4-5 metres long with an averagediameter of 4 centimetres; It is divided into three sections: the duodenum, the jejunum and the ileum.
The duodenum is the section most involved in the digestive processes, whereas the main purpose of the jejunum and ileum is to absorb nutrients and water.
The duodenum receives pancreatic enzymes and bile, which are responsible for digestion. The absorption of nutrients starts in the duodenum, continues in the jejunum and is completed ileum.
The small intestine is lined with villi, which are covered by microvilli, structures that are responsible for the small intestine’s absorption capacity.
The large intestine begins at the ileocaecal valve and ends at the anus; it is approximately 2 metres long but with a much larger diameter than that of the small intestine.
Anatomically, it is divided into six sections: caecum, ascending colon, transverse colon, descending colon, sigmoid colon and rectum.
The main function of the large intestine is to store the residues of the digestive process that occurred in the small intestine and help their expulsion.
In the colon, there is significant absorption of water, electrolytes and many vitamins.
Note that there is a difference: food-based vitamins are absorbed in the small intestine, while the vitamins absorbed by the colon are mostly produced by the intestinal microbiota which, albeit also present in the small intestine, reach maximum density in the colon.
These microorganisms synthesise in particular vitamin K and some B vitamins.
In addition, the intestinal microbiota produces many short-chain fatty acids, in particular butyric acid and propionic acid, which are also absorbed in the large intestine, and these are used by the body to store energy.
Common gastrointestinal disorders
Gastrointestinal disorders are frequently experienced in the colon and rectum.
Some of the most common gastrointestinal disorders are: diarrhoea, abdominal swelling, stomach ache and lazy bowel syndrome (constipation).