Small intestine is one of the most important organs of human body made up of 100 million nerve cells, designed for the absorption of food. The process of digestion starts in the mouth and completes in the small intestine. The food we eat, moves down to stomach through esophagus. The stomach stores the food, release hydrochloric acids, mucus and digestive enzymes so that foods can be broken down and churns into Chyme.
The role of small intestine begins from receiving Chymes from the stomach. Let us understand the design and parts of small intestine. Small intestine is a long narrow folded coiled tube of length 6-9 meters. The length of it is proportional to your height. It is divided into 3 parts.
Duodenum- first part of the small intestine
This is a “c” shaped tube that receives Chymes from the pyloric end of the stomach. It is the shortest and the widest part of small intestine. Its length is approximately 10 inches.
The most of the final breakdown of food happens here. The liver, pancreas and gall bladder are connected to Duodenum through hepopancreatic duct. Each of this has special function that helps in digestion of the food. The pancreas release bicarbonate to neutralize acids from stomach, Lipase to break down fat, Proteases to break down proteins and Amylase to breakdown carbohydrates. Duodenum receives all these through the duct opening called ampulla of vater. Brunner’s gland is also found in the Duodenum, which releases mucus, which also subsequently reduce acidity. The liver and gall bladder sends bile juice to the duodenum. If you notice here, the main thing happening here is the reduction of acid level of the food released by stomach so that digestive enzymes can work.
The wall of Duodenum secrets so many hormones. Some of the important Hormones released by the wall of Duodenum are
Enterogasterone/Gastro Inhibitory Peptide
If you remember, the stomach releases gastric juices to break down the food before it was passed on as Chyme to Duodenum. The stomach Inhibitory Juices, released by the walls of Duodenum inhibits or stops those gases to be released anymore as they are no more required.
Secretin
It is also known as fireman of the intestine. This is the first hormone discovered. The main function of this hormone is activating the non-enzymatic part of the pancreatic juice. By doing so it helps in releasing ions NA+, K+ , HCO3. The purpose of this is to reduce the acidity and increase the alkalinity of the food.
Pancreozymin
This hormone does exactly opposite of what Secretin did. This activates the enzymatic part of the pancreatic juice. This helps in breaking down proteins and fats into smaller molecules that can be absorbed in your small intestine.
Cholecystokinin
This contracts Gall bladder, since the bile juice in the gall bladders are thick. It takes some efforts to get that released. The CCK or Cholecystokinin presses and contracts gall bladder to get the Biles released and flow into the Duodenum. This makes food even more alkaline and helps enzymes to work better on food for digestion.
Jejunum-second part of the small intestine.
The length of this organ is almost 2.5 Meters. This is the main are where the digestion happens. It has millions of fingers like projections called Villi and microvilli. As you have noticed that all the efforts have already been made by the hormones in the Duodenum are to make the food Alkaline, the PH level of Jejunum is in between 7-8. There are numerous folds found, which forms crypts like structure called Crypts of Lieberkühn. This is also called intestinal gland, at this place numerous digestive juices are released called succus entericus.
Ileum-third part of small intestine
This is the longest part of the alimentary canal or small intestine. The length of this is almost 3.5 meters. The section is meant for absorption. They have club or mushroom shaped Villi. The ileum is the last part of small intestine. It is connected to the colon, the first portion of the large intestine. The valve that connects ileum and colon is ileocecal valve. The all absorption of food happens at this area. The ileum has blood vessels all across. The absorbed food is then transported to all cells through blood vessels and arteries.
