The small intestine is a very essential organ in the digestive process. It is the part of the digestive system that follows directly the stomach in arrangement inside the body. As the upper border of the small intestine is the stomach, the lower border is the large intestine. The small intestine is where most of the digestive process takes place together with the absorption of different nutrients as well.The Structure of The Small Intestine
The small intestine measures 6.9 to 7 meters in adult males and about 7 .1 meters in females. This is just an average anyway and there can still be a lot of variations when it comes to the length of the small intestine. The range is usually between about 4.6 meters to 9.8 meters. The diameter measures about one to one and a half inch.The Different Parts Of The Small IntestineCredit: http://www.butler.org/body.cfm?id=125&chunkiid=14864
There are actually three different parts of the intestine each serving their respective functions. These are the duodenum, the jejunum and lastly, the ileum. The duodenum is the upper portion of the small intestine while the rest follows , the jejunum and lastly the ileum. Each part has their respective characteristics when it comes to each of their layers.
Comparing The Different Parts Of The Intestine
First of all, the duodenum, the jejunum and the ileum all have normal structure of their serosa. Normal structure means that there are no extra structures or specialized parts located in the said layer. For the muscularis externa, all the three parts of the small intestine have circular and even longitudinal layers with a known myenteric plexus or the Auerbach’s plexus in between such layers. The submucosa of the duodenum has specialized glands known as the Brunner’s glands together with the submucosal plexus known as the Meissner’s. On the other hand, the submucosa of the jejunum and the ileum does not have any Brunner’s glands. When it comes to the mucosa or the muscularis mucosa, all of the three parts of the small intestine have normal structures similar to that of their serosa. When it comes to the lamina propria part of their mucosa, only the ileum differs because it has specialized structures known as the Peyer’s patches. Lastly, the intestinal epithelium part of the mucosa for the three parts of the small intestine have goblet cells and Paneth cells together with simple columnar cells. The only difference arises with the length of the villi because the length of that of the jejunum is very long while that of the ileum is very short.Credit: http://www.constipationadvice.co.uk/understanding_constipation/normal_digestive_system_plain.php
Digestion Process With The Small Intestine
The food from the stomach is directed into the intestine through the means of pylorus marked by the pyloric sphincter at the end of the stomach and just about the beginning of the small intestine. The small intestine is known in the process of digestion because it is where the latter usually takes place the most. The enzymes required for digestion are produced mostly in the small intestine as secreted by the pancreas. These enzymes from the pancreas pass through the pancreatic duct through which they enter the small intestine. Once the food reaches the small intestine, hormones in the form of cholecystokinin are produced in the small intestine and eventually allow the enzymes from the pancreas to enter. Another hormone in the form of secretin also allows the small intestine to release bicarbonate which is used to effectively neutralize that acid that comes from the stomach in the small intestine.Credit: http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookDIGEST.html
Absorption Process With The Small Intestine
By means of diffusion, the food that has already been digested eventually passes through the blood vessels in the small intestinal wall. As what have been previously stated, the small intestine is the site in the digestive tract where most of the absorption of different nutrients takes place. There are simple columnar and epithelial tissues that are lining the wall of the small intestines which aid in absorption. There are also folds along the mucosa known as the plicae circulares which are permanent structures in the mucosal wall. These plicaes are actually different from the rugaes because the former is permanent while the latter are just permanent structures that facilitate peristalsis or contraction. The plicaes are also unique in a sense that they are lined with microsopic and finger-like features known as villi. There are even smaller forms known as microvilli. These structures are the ones responsible for the absorption of the nutrients from the food you eat.
The villus or the finger like projections in the small intestines has their own set of capillaries and lacteals or fine lymphatic vessels. This ensures that they are able to maintain their normal functioning very well. These capillaries and lymph vessels allows the transport of different nutrients absorbed by the small intestine into different parts of the body that needs them. The capillaries are responsible for the transport of the carbohydrates and the amino acids while the lacteals or the fine lymphatic vessels are the ones responsible for the transport of lipids. This process is known as diffusion. After this absorption, the other parts of the food that remains undigested is eventually passed through the large intestine.Credit: http://jp.physoc.org/content/587/1/195/F7.expansion
The Absorption Of Nutrients in the Small Intestine
The specific part of the small intestine where most of the absorption takes place is the middle part or the jejunum. But, there are several exceptions that should be considered. For example, the iron content of food is usually absorbed in the duodenum and not in the jejunum. The bile salts together with Vitamin B12 are absorbed in the lowest part of the ileum. Fructose, a type of sugar, is absorbed by the means of facilitated diffusion. Water and lipids are then absorbed in our body by the means of passive diffusion.
These are some of the most important details that you need to know about the small intestine. The small intestine is definitely a very significant part of the digestive system because it facilitates most of the body’s absorption of nutrients from food intake.
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