Small intestine


The small intestine is part of the organs that make up the digestive system, it is located between the pylorus and the ileocecal junction. This in turn is divided into three parts, which are the duodenum, jejunum and ileum. The duodenum is united with the pylorus and receives the gastric content, then comes the jejunum and finally the ileum, which communicates with the first portion of the large intestine, the cecum.


What is the small intestine?

The small intestine is a tubular organ that is part of the organs that make up the digestive system . It is located in the abdominal cavity, between the pylorus and the ileocecal junction . It is divided into three parts, which are the duodenum, jejunum and ileum.

  • Definition
  • Small intestine characteristics
  • Function
  • Parties
  • Layers
  • Location
  • Villi
  • How does it work
  • Secretions
  • Small intestine diseases
  • Care
  • How big is
  • What is absorbed in the small intestine
  • Importance


It is a tubular organ of the digestive system that joins the stomach with the large intestine . The small intestine digests food material and absorbs nutrients, contributing to the digestion process.


Small intestine characteristics

The main characteristics of the small intestine are as follows:

  • The small intestine is the longest portion of the digestive tract, measuring approximately 8 meters in length.
  • Pinkish in color .
  • It is folded within the abdominal cavity.
  • It is one of the organs with the most cell turnover , its entire internal surface is renewed every 5 days.
  • As the individual grows, the small intestine increases in size about 20 times.


  • Digestion: the small intestine contributes to 90% of digestion , since the stomach and colon carry out the remaining 10%. Digestion in this organ is carried out by bile acids and enzymes that degrade food for proper absorption.
  • Absorption: through the villi, the small intestine absorbs nutrients from food.
  • Barrier: ensures that the food content inside through the intestinal mucosa.
  • Immunity: the cells of the intestinal epithelium form a protective barrier against microbes ; They detect microbes, trap them in mucus, and activate the immune response.


The parts of the small intestine are:

  • Duodenum: it is the first portion of the small intestine, the shortest and widest. It borders the pancreas in the shape of a C and goes from the pylorus to the duodenojejunal junction The duodenum is divided into 4 portions: the upper portion, which measures approximately 5 cm and is attached to the pylorus; the descending portion is the longest and measures 7 to 10 cm and is crossed by the transverse mesocolon; the horizontal portion measuring 6 to 8 cm is infracolic, passes in front of the aorta and the vertebral column and is directed from right to left; and the ascending portion that measures approximately 5 cm and is located to the left of the ascending aorta.
  • Jejunum and ileum: they go from the duodenojejunal flexure to the ileocecal junction. They measure 6 to 7 meters. The jejunum represents 40% and the ileum 60%. There is no fixed limit between the two and their characteristics are very similar.


The duodenum is made up of 3 layers:

  • Mucosa: in their grooves contain glands intestinal or Lieberkühn and duodenal Brunner glands or that disappear after biliopancreatic mouth.
  • Submucosa: formed by dense, irregular and loose connective tissue that allows the mucosa to slide over the muscle layer.
  • Muscular: contains an internal circular layer and an external longitudinal layer.

The jejunum and ileum have the same layers as the rest of the digestive tract and are 5:

  • Serosa: contains a simple serous squamous epithelium.
  • Subserosa: it works as a support for the serous layer, since it is a layer of connective tissue.
  • Muscular: composed of a longitudinal layer with cells in long helical turns and a circular layer with cells in dense helical turns.
  • Submucosa: formed by a connective tissue and contains collagen, blood vessels and nerves.
  • Mucosa: contains simple columnar epithelium, connective tissue, and a muscular sheet.


The small intestine is located in the abdominal region , between the stomach and the large intestine or colon. It goes from the pylorus to the ileocecal junction .


They are extensions of the innermost layer of the small intestine. They are covered by microvilli and inside they contain capillaries, lymphatic ducts and smooth muscle fibers . Its height decreases from the duodenum to the ileum, from 1.5 mm to 0.5 mm. Their function is to capture nutrients and transport them to the blood. Villi

How does it work

Food is processed first in the mouth and stomach, where the bolus or chyme is formed. Then the chyme is called chyle, it reaches the duodenum together with the bile salts from the gallbladder and pancreatic enzymes that will help the degradation of nutrients. In the small intestine, vitamins, salts, water, carbohydrates and other nutrients are absorbed through the intestinal villi, which not only capture and absorb these nutrients, but also lead them to the bloodstream. In addition, the small intestine is responsible for carrying the remaining food to the large intestine so that it is later expelled from the body.


The small intestine secretes mucous and watery substances . The mucus comes from Brunner cells and Lieberkühn crypts; This is an alkaline mucus to protect the duodenal wall from acidic gastric juices from the stomach. On the other hand, the water content comes from the epithelial cells and this is absorbed by the villi.

Small intestine diseases

  • Duodenal ulcer
  • Malabsorption syndrome
  • Celiac Disease
  • Irritable bowel syndrome
  • Intestinal obstruction
  • Paralytic ileus
  • Diverticulosis
  • Meckel’s diverticulum
  • Short bowel syndrome
  • Crohn’s disease
  • Bowel motility disorders
  • Anger
  • Taeniasis
  • Intestinal polyps
  • Tumors


To avoid diseases of the small intestine, it is necessary to adopt healthier habits that help to carry out a good digestion. It is recommended:

  • Drink 8 glasses of water a day.
  • Have a balanced diet.
  • Eat foods rich in fiber.
  • Avoid foods with a lot of salt and cholesterol.
  • Walk 20 minutes a day or exercise.
  • Avoid excess medications.
  • Avoid the consumption of alcoholic drinks.
  • Control emotions and stress.

How big is

The small intestine is about 8 meters long.

What is absorbed in the small intestine

Throughout the entire small intestine many nutrients are absorbed, such as: fats, amino acids, carbohydrates, water, magnesium, zinc, sodium, potassium, iron, chlorine, calcium, fat-soluble vitamins (A, D, E, K ), bile acids, vitamin B1, B2, B9 and B12.


The importance of the small intestine lies in the fact that it is a fundamental organ for the digestion process; That is why we must embrace healthier eating habits, accompanied by a little exercise.

Leave a Comment