Small Intestine

Small intestine, the primary gastric organ in human body, is a part of digestive system. Most of the digestive activities occur in this organ. So, what is small intestine can be answered as – it is a tubular element within abdominal cavity which carry food from stomach to colon. 

Small Intestine Structure 

It is a coiled tube that is further sub-divided into three components from proximal part (stomach) to distal. All three components aid digestion in small intestine. The parts of small intestine are –

  1. Duodenum

The duodenum is the shortest region of about 25.4 cm. It creates a C-shaped curve at head of the pancreas before joining the jejunum. The entire length of duodenum can be divided into four parts – superior, descending, horizontal and ascending duodenum. 

  1. Jejunum 

Jejunum is about 0.9 metres long and stretches from duodenum to ileum. When it joins ileum, there is usually no clear demarcation between the two regions. 

  1. Ileum 

The longest part of the small intestine is ileum which is about 1.8 metres in length. It has more mucosal folds compared to jejunum and joins the large intestine through ileocecal sphincter. Ileum also helps in the process of digestion of food in small intestine. 

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Do You Know?

Here is an interesting fact about small intestine. It is the longest component of our digestive tract. It is approximately three times the length of our body. Also, ingested food stays for about four hours in the small intestine. It takes this long because 90% of nutrients from our ingested food is absorbed into blood through small intestine. 

Role of Small Intestine 

Read on to know the role of small intestine in digestive system. 

Most of the digestion and absorption of food occurs in small intestine, and the remaining takes place in stomach and large intestine. 

  1. Digestion of Proteins

Proteins and amino acids are broken into peptides by different enzymes. Such chemical breakdown starts in stomach and continues till large intestine. 

  1. Digestion of Lipids 

Enzymes from pancreas and bile salts from liver break down fatty acids so that these can enter intestinal villi for absorption. 

  1. Digestion of Carbohydrates 

Carbohydrates are broken down into monosaccharides by intestinal bacteria. 

  1. Absorption 

After the nutrients are broken down, those are absorbed by inner walls of the small intestine and transported into the bloodstream. Absorption takes place with the help of finger-like tissue called villi. 

What Happens to Food in the Small Intestine?

The following account describe the process of digestion in small intestine. 

The digestion of proteins and carbohydrates start in the stomach and completes in small intestine with the help of pancreatic and intestinal juice. However, lipids reach intestine undigested. 

The combination of pancreatic juice and intestinal juice creates a liquid medium that helps in absorption. The digestive enzymes are secreted from plasma membrane of microvilli.

Chemical digestion requires chyme and its mixing with pancreatic juice and bile. It helps in an upward adjustment of the low pH of chyme. 

Test Your Knowledge 

i. The digestive hormones – cholecystokinin and secretin are secreted by 

(a) Duodenum. 

(b) Ileum.

(c) Stomach. 

(d) Oesophagus. 

ii. Which of the following forms the opening of Ileum?

(a) Villi.

(b) Sphincter.

(c) Mitral valve. 

(d) Ileocecal valve. 

[Solutions]

i. (a) Duodenum 

ii. (d) Ileo caecal valve 

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FAQ (Frequently Asked Questions)

1. What is the Length of the Small Intestine?

Ans. The small intestine is about 20 feet or 6 metres long. It is so long because it requires maximum surface area for digestion and absorption of nutrients. 

2. Which are the Three Parts of the Small Intestine?

Ans. The parts of the small intestine are – duodenum, jejunum, ileum. All these parts are instrumental in complete absorption of nutrients from food. 

3. What is the Function of the Small Intestine?

Ans. The main small intestine function is digestion and absorption of food. It acquires minerals and nutrients available in the ingested food.