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small intestine5 Interesting Facts You Need To Know About Your Small Intestine. The intestines are a very vital part of your digestive system. They lie between the stomach and the anus. We have  two major sections: the small intestine and the large intestine.

In this article we will  focus more on the small in.testine.

The small intestine also known as ‘small bowel’ in humans is a long, winding tube connected to the stomach. It handles absorption of about 95% of nutrients from food during the digestive process.

Here are 5 interesting facts you need to know about the small intestine:

1.It is actually really long

Although, judging by its name you may want to conclude that the organ is small in size. Well, that’s not the case.

The words “small” attached to the name of this  intestine can be a bit misleading.

The small intestine is termed ‘small’ not in terms of length but for its narrow lumen and smaller diameter. It has a comparatively smaller diameter than the large intestine.

On average, the diameter of the large intestine of an adult human measures approximately 3 times the diameter of the small intestine.

So, how long is the small intestine?

The small intestine is the longest part of the digestive system, having a length of about 6 meters (20 feet). That measures to about the size of a story building if it’s straightened out!


2. It is a three-part organ

The small intestine is very efficient, it’s an invisible worker that plays its part in the seamless digestive process. The organ is a divided into 3 parts that include:

  • The duodenum
  • The jejunum
  • The ileum

The duodenum is the shorter than the jejunum, while the ileum is the longest part of the small intestine.
There is actually division of labor among different segments. In other words, each of the small intestine parts must perform a specific assigned task. Here’s a summary of the functions of each segment.


The first and shortest segment of the small bowel, duodenum connects the stomach to the jejunum. This C-shaped hollow tube measures around a foot in length. Duodenum receives food from the stomach in the form of chyme and mixes it with bile juice and the pancreatic secretions. It neutralizes the partially digested food with the help of alkaline mucus containing a high concentration of bicarbonate ions. The mucus is secreted by the Brunner’s glands present only in the duodenum.

The enzymatic secretions help in the digestion of carbohydrates, proteins and fats. So, the process of chemical digestion that started in mouth gets completed here. It also prepares food for absorption in microvilli.


The jejunum is the second or middle part of the small intestine. In terms of length, it is longer than duodenum and shorter than ileum. Measuring around 8 feet.

While the duodenum carries out and completes the chemical digestion, the jejunum is the principal site for the absorption of nutrients from the digested food. This is the part where over 90% absorption of the foodstuffs takes place.

Food is absorbed into the bloodstream through finger-like projections called villi. Though villi are present across all segments of small bowel, they are longer and more active in the jejunum. The folds in the epithelium, villi and microvilli collectively contribute to incredibly increase the surface area for absorption.

The jejunum also has a pH between 7 and 9. This means it is slightly alkaline.


The third and longest segment of small bowel is the ileum, it is about 12 feet long.
The layers of longitudinal and smooth muscles in the ileal wall are thinner than those of other parts of small intestine.

Regarding its role in digestive system, the ileum contains receptors for absorption of vitamin B12 and bile salts. Meanwhile, it also absorbs the leftover nutrients from the digested food.

In 1667, Hans Conrad Peyer, a Swiss anatomist, discovered bundles or patches of lymphatic cells in ileum (the lymphatic system is part of the immune system that protects the body from infections). These patches are named after him as Peyer’s patches.

They can be seen with the naked eye as elongated thickened areas. We all have about 30 to 40 of such patches in our small intestines.

3.Its surface area is about the size of a tennis court

Asides being very long, the small intestine has an enormous surface area. The absorptive surface area of the small in.testine is actually about 250 square meters (almost 2,700 square feet), about  the size of a tennis court! How is this even possible?

The small intestine has some features which allow it to have such a huge absorptive surface area packed into a relatively small space.

These features are:

The Villi: The folds form numerous tiny projections which stick out into the open space inside your small intestine and are covered with cells that help absorb nutrients from the food that passes through.

The Microvilli: The cells on the villi are  full of tiny hairlike structures called microvilli. They helps increase the surface of each individual cell, which means that each cell can absorb more nutrients.

Mucosal folds: The inner surface of the small intestine is made up of circular folds. This helps to  increases the surface area and also helps regulate the flow of digested food through your intestine.

4. It really does not fancy acidity

The stomach produces hydrochloric acid. This helps to begin digestion, and it kills many harmful microorganisms that might have been swallowed along with the food. The enzymes in the stomach work best in acidic conditions – in other words, at a low pH. This acidity is what reason what causes peptic ulcers which are ‘wounds in the stomach wall’ that can cause bloody or black stools.

When food is then processed by the stomach, the end result is a very acidic mixture of proteins, acids, and other substances that the body needs.

After the stomach, food travels to the small intestine. The enzymes in the small intestine work best in alkaline conditions, but the food is acidic after being in the stomach. A  green pigment called bile neutralises the acid and provides the alkaline conditions needed in the small intestine.

The only problem is that the small intestine really hates acidic items. To counter these acids, the small intestine will produce secretions that are very alkaline in nature so that the food can be processed. Sometimes these alkaline materials come from the wall of the intestine, while others might come from the liver or the pancreas.

The intraluminal pH is rapidly changed from highly acid in the stomach to about pH 6 in the duodenum. The pH gradually increases in the small intestine from pH 6 to about pH 7.4 in the lowermsost part of the ileum.

5.It also shares in the hormone secreting responsibility.

The small intestine is indeed an  organ with enormous responsibility ; it simply an organ that our body will always be grateful it has.

Do you know it also secretes hormones?

Different parts and cells of small intestine are specialized for secreting various useful hormones which facilitate the process of digestion in different ways. Here are some of the hormones that are secreted:

The epithelial cells in the small intestine secrete the secretin hormone. It stimulates the pancreas and liver to release bicarbonate-rich fluids into the lumen through pancreatic and bile ducts, respectively. These bicarbonate-rich fluids are used for the neutralization of acidic food from stomach and emulsification of fats.

The enteroendocrine cells in the duodenum are specialized for synthesizing and secreting cholecystokinin hormone. The presence of this hormone enables the pancreas to  release digestive enzymes and helps the gallbladder empties bile into the intestinal lumen.

One interesting function of this hormone is that it also helps in suppressing hunger.

Gastric Inhibitory Polypeptide:
The K cells in the mucosa of duodenum and jejunum help synthesize gastric inhibitory polypeptide (GIP) as an endocrine hormone. It is transported by blood and blocks the secretion of hydrochloric acid (HCL) into the stomach.

The GIP hormone also stimulates the beta cells in the pancreas to increase the secretion of insulin. Insulin, helps regulate the level of glucose in the blood.

Crypts in the duodenum and jejunum contain numerous endocrine M cells which secrete motilin hormone. The hormone helps in improving peristalsis and preparing the digestive system for the next meal. Motilin is also known as “the housekeeper of the gut”.

It also stimulates the production of pepsin, an enzyme that digests proteins in the stomach.


The small intestine is an incredible work of nature. It allows us to digest foods quickly and effectively so that we have the energy we need. That’s why taking care of it is so important. Without your small intestine, the process of digesting food would become incredibly difficult.

Author Profile :- Ademola Adewuyi has a degree in Human Anatomy and is a content crafter at 25 Doctors, a website where you can ask doctors medical questions online.


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