Small Intestine and Large Intestine

The gastrointestinal tract (GI) is a vital part of the human digestive system. Also known as the digestive tract, the GI helps in breaking down the ingested food. The nutrients are then absorbed, and the undigested food is released from the body. The whole process of nutrient absorption and digestion of food keeps the overall body healthy. The two major sections involved are the small intestine and the large intestine. This article will discuss them in detail and state the difference between the small and large intestines. 

Small Intestine: Definition

The small intestine is a part of the digestive tract present between the stomach and the large intestine. It is around 20 feet or 6 metres extending from the pyloric orifice to the ileal orifice. It is referred to as a small intestine because it is narrower than the large intestine.  

Parts of Small Intestine

The small intestine is structurally divided into three parts. These are called Duodenum, Jejunum, and Ileum. All three combine to form the small intestine. 

1. Duodenum: It begins at the end of the pyloric sphincter, covers the head of the pancreas in C-shape, and ends at a point called the duodenojejunal flexure. When food is present in the duodenum, it signals the organs to send digestive juices. All the ducts of major organs like the liver, pancreas, gallbladder feed into the duodenum. 

2. Jejunum: It begins at the duodenojejunal flexure and is located on the left side of the upper abdomen. The chemically digested food enters the jejunum from the duodenum. Here, the muscles churn the food to mix it with the digestive juices. The food then moves forward through muscle movement called peristalsis. 

3. Ileum: It is the longest part of the small bowel and is located on the lower right side of the abdomen. The Ileum ends in the ileocecal junction, where the large intestine begins. The Ileum is responsible for aiding food movement towards the large intestine through the ileocecal valve. Hormones and nerves signal this valve to open and let the food pass through. It then closes to keep the bacteria from entering the small intestine. 

Functions of Small Intestine

The small intestine plays a crucial role in digesting the ingested food. It aids in food digestion using bile and pancreatic juices received through the pancreatic duct. The organ mostly absorbs the nutrients from the food and liquids. Here are the major functions that the small intestine performs in the human body.

• Systematic breakdown of the ingested food

• Nutrients absorption

• Water extraction

• Helps in the movement of food along the gastrointestinal tract

Large Intestine: Definition

The large intestine or the large bowel is a vital part of the gastrointestinal tract, which helps in the reabsorption of water from the undigested food in vertebrates. 

The large intestine is interchangeably called the colon. However, several sources define the large bowel to be consisting of the cecum, colon, rectum, anus. 

The length of the large intestine is around 1.5 metres. That means it covers one-fifth of the total length of the gastrointestinal tract in humans. 

Parts of Large Intestine

The large intestine starts at the right ilium of the pelvis. Here it meets the small intestine (cecum). It then ascends the abdomen and crosses the abdominal cavity. The large intestine finally descends to the rectum. The endpoint of the large intestine is called the anus. The large intestine is made of four major sections, namely,

1. Caecum: It is the first part of the large intestine surrounded by numerous folds and pockets. The caecum is located in the right iliac fossa of the abdomen. 

2. Colon: the various parts of the colon are described below. 

• Ascending colon

It is the first section of the large intestine. It starts at the right side of the ilium (beyond the cecum, to be specific). It goes upwards to the area just below the diaphragm. 

• Transverse colon

 It is the part of the large bowel that crosses the abdominal cavity from the right to the left side of the human body. 

• Descending colon 

The descending colon is the portion of the large intestine that begins just below the diaphragm and ends in the left pelvic region. It goes downwards along the left side of the abdomen. 

• Sigmoid colon

The S-shaped section which connects the rear end of the colon to the rectum is called the sigmoid colon. It is located at the bottom left of the abdomen in the human body. 

3. Rectum: It begins at the junction of the sigmoid colon and rectum, known as the rectosigmoid junction, and ends at the starting of the anal canal. The rectum temporarily stores the faeces and aids in defecation. 

4. Anal canal: It starts at the anorectal junction (meeting point of the rectum and anal canal) and ends in the anus. It helps in the release of the faeces from the body. 

Functions of Large Intestine

The main functions of the large intestine are:

• Production and absorption of vitamins such as riboflavin, Vitamin K, thiamine, etc.

• Absorption of water from undigested food 

• Recycling of several nutrients

• Formation of faeces

• Absorption of electrolytes such as sodium, chloride, magnesium from undigested food.

• Propelling the faeces towards the rectum.

Small Intestine and Large Intestine: Difference

Conclusion 

The small intestine plays a vital role in food digestion, whereas the large intestine forms the faeces and aids in defecation. The overall process is essential for maintaining a healthy body. Both the intestines have different muscle arrangements, nerve supply, and histology. In this article, we have discussed the anatomy, functions, and the difference between the small intestine and large intestine.