The processes that happen to our digested food once it leaves the stomach are the most important as this is where the nutrients from the food we eat is absorbed.
Below explains how all of the components beyond the stomach fit together and their roles within digestion. I have put words in bold that refer to the picture above.
The duodenum (pictured in between the gall bladder and pancreas)
is the start of the small intestine and regulates the entering of chyme (stomach contents). As chyme enters it stimulates the release of cholecystokinin (no idea how to pronounce this one but all we need to know is that it is a hormone) secreted by cells in the duodenum.
As a result of this hormone the gall bladder, which stores bile that has been made in the liver, empties itself almost completely when it gets this message that food is arriving from the stomach. Between meals, it only lets out a dribble of bile. The bile travels down the bile duct to the duodenum. The pancreatic duct meets it there through a ring of muscle, or sphincter, controlling the release of bile pancreatic fluid into the duodenum.
The duodenum occupies a key position in the digestive system, linking the upper part of the mouth, gullet and stomach with the bowels. It lies just above the navel in a circle hugging the head of the pancreas. It also has a key role in the digestive process, as food arriving from the stomach is only half-digested so this is where essential digestion takes place. This includes starches and fats in particular but proteins are also incompletely digested. Fats at this point are virtually unchanged, it is only when it reaches the duodenum the digestion of fats can actually begin.
Digestive enzymes made in the pancreas, and bile manufactured by the liver, are both poured onto the part-digested food in the intestine, in response to an electro-chemical signal that fatty food is on its way.
First, bile acts on the fats in the food, breaking them down, then pancreatic enzymes, complete the digestion of the remaining starches, fats and proteins.
The enzyme lipase from the pancreas emulsifies the fats, breaking down the fat globules (known as lipids made up of fats and oils) into smaller globules (these are known as fatty acids and glycerol). Bile completes this process. It is only when globules are microscopically small that they can be absorbed into the bloodstream. If this does not happen fatty diarrhoea will be a result.
Which brings us onto the middle part of the small intestine is the jejunum. Villi increase the surface area inside the jejunum, these finger-like projection are one cell thick with a good blood supply, designed to easily absorb digested food molecules quickly into the blood stream by diffusion. (Going back to my GCSE Science here!)
The final section of the small intestine is the ileum. Any further products of digestion are absorbed here and due to the bigger pores so can vitamins such as vitamin B12, minerals and salts. The main difference is the high abundance of lymphoid tissue, this is part of the immune system to protect the body from invasion in the gut. Our digestive tract has the largest mass of lymphoid tissue in the body and is key to protecting us from infection.
Fibre, water and vitamins carry onto be broken down further in the large intestine. Water that has been used in the digestion process is now reabsorbed in the colon and any undigested food and fibre is sorted in the rectum which is then eliminated through the anus (and we all know what happens here).
There’s a ton of more processes and I have tried to keep it as informative but also understandable for anyone to read as well. I hope this gives you an insight into how amazing our digestive system is and how important it is to treat it well and with respect.