What Is an Alimentary Canal and What Are Its Main Parts?

Introduction

The alimentary canal, also known as the digestive tract or gastrointestinal tract, is a long tube-like structure that starts from the mouth and ends at the anus. It is responsible for the digestion and absorption of nutrients from the food we eat, as well as the elimination of waste products from the body. In this tutorial, we will discuss the main parts of the alimentary canal and their functions.

Alimentary Canal

The different parts of the alimentary canal and their main functions are as follows −

• Mouth − The mouth is the starting point of the digestive system. The teeth, tongue, and saliva in the mouth work together to break down the food and mix it with digestive enzymes.

• Pharynx − The pharynx is a muscular tube that connects the mouth and the esophagus. It helps in swallowing the food.

• Oesophagus − The oesophagus is a muscular tube that connects the pharynx to the stomach. It carries the food to the stomach by rhythmic contractions called peristalsis.

• Stomach − The stomach is a muscular sac that churns and mixes the food with stomach acid and digestive enzymes. It further breaks down the food into a liquid called chyme.

• Small Intestine − The small intestine is a long, narrow tube where most of the digestion and absorption of nutrients takes place. It is divided into three parts - the duodenum, the jejunum, and the ileum. The small intestine receives digestive enzymes and bile from the pancreas and liver, which help in breaking down the food further. The walls of the small intestine have finger-like projections called villi, which increase the surface area for nutrient absorption.

• Large Intestine − The large intestine is a wider tube that absorbs water and electrolytes from the undigested food matter. The remaining waste is stored in the rectum until it is eliminated from the body through the anus.

Mouth

The mouth is the first part of the digestive system, responsible for the initial mechanical and chemical digestion of food. It has various parts that work together to break down food into smaller particles, making it easier to swallow and digest. The different parts of mouth and its functions are given below −

• Teeth − Teeth are hard, calcified structures in the mouth that chew and grind food into smaller pieces, increasing its surface area for better digestion. Humans have four types of teeth: incisors, canines, premolars, and molars, each with a unique shape and function.

• Tongue − The tongue is a muscular organ in the mouth that helps in chewing and swallowing food. It also plays a vital role in speech, taste perception, and maintaining oral hygiene.

• Salivary Glands − The salivary glands are three pairs of glands in the mouth that secrete saliva, a fluid containing enzymes that break down starches and lubricate the food for easier swallowing.

The Functions of the Mouth Include

• Mechanical digestion − Teeth and tongue work together to break down food into smaller particles, making it easier to swallow and digest.

• Chemical digestion − Saliva contains enzymes that break down starches into simpler sugars, initiating the process of chemical digestion.

• Lubrication − Saliva moistens the food, making it easier to swallow.

Pharynx

The pharynx is a small cavity behind the mouth and nasal cavity that connects the mouth to the esophagus. The food is propelled through the pharynx and into the esophagus by a series of coordinated muscle contractions known as peristalsis.

Oesophagus

The oesophagus is a muscular tube that connects the pharynx to the stomach. It uses peristalsis to move food down towards the stomach. The lower esophageal sphincter (LES) is a ring of muscle at the bottom of the esophagus that opens to allow food to enter the stomach and closes to prevent stomach contents from flowing back into the oesophagus.

Stomach

The stomach is a muscular sac that is located in the upper left side of the abdomen. It continues the process of breaking down food that was started in the mouth. The stomach secretes gastric juice, which contains enzymes and hydrochloric acid that further break down the food and kills bacteria. The stomach also mixes the food with gastric juice to form a semi-solid mixture called chyme.

Small Intestine

The small intestine is a long, narrow tube that is a part of the digestive tract, and it plays a crucial role in the digestion and absorption of nutrients from the food we eat. The small intestine is divided into three parts: the duodenum, the jejunum, and the ileum.

Duodenum

The duodenum is the first part of the small intestine and is approximately 25cm long. It receives partially digested food from the stomach, along with bile and pancreatic juice, which help in the breakdown of fats and proteins. The duodenum also secretes its digestive enzymes, including sucrase, maltase, and lactase, which break down carbohydrates further. The walls of the duodenum have glands that produce mucus to protect the duodenal lining from stomach acid.

Jejunum

The jejunum is the second part of the small intestine, which is approximately 2.5 meters long. This part of the small intestine absorbs most of the nutrients from the food, including proteins, carbohydrates, and fats. The walls of the jejunum have villi, small finger-like projections that increase the surface area for nutrient absorption. The villi are covered in microvilli, which further increase the surface area, enabling the absorption of nutrients into the bloodstream.

Ileum

The ileum is the final part of the small intestine, which is approximately 3.5 meters long. It absorbs remaining nutrients that were not absorbed by the jejunum, including vitamin B12 and bile salts. The walls of the ileum also have villi, but they are shorter and more widely spaced than those in the jejunum. The ileum ends at the ileocecal valve, which controls the flow of material into the large intestine.

Large Intestine

The large intestine, also known as the colon, is the final part of the digestive system, which follows the small intestine. The large intestine is responsible for the absorption of water, electrolytes, and certain vitamins, and the formation and elimination of feces from the body.

Cecum

The cecum is the first part of the large intestine, which receives the contents from the ileum of the small intestine. It also contains a small projection called the appendix, which has no known digestive function in humans but may play a role in immune function.

Colon

The colon is the longest part of the large intestine, which is divided into four sections: the ascending colon, the transverse colon, the descending colon, and the sigmoid colon. The colon absorbs water and electrolytes from the undigested food matter that enters from the small intestine. The colon also houses bacteria that help in the fermentation of indigestible carbohydrates, producing short-chain fatty acids that provide energy to the colon cells.

Rectum

The rectum is the final part of the large intestine, which stores feces until they are eliminated from the body through the anus during a bowel movement. The rectum has stretch receptors that trigger the urge to defecate when the rectum is full.

The functions of the large intestine include

Absorption of Water and Electrolytes − The large intestine absorbs most of the remaining water and electrolytes from the undigested food matter, resulting in the formation of solid feces.

Formation and Storage of Feces − The colon compacts the undigested food matter and bacteria into solid feces and stores them in the rectum until they are eliminated from the body.

Conclusion

In conclusion, the alimentary canal is a complex system that involves several organs working together to break down, absorb, and eliminate food. Understanding the functions of each part of the alimentary canal is essential to maintaining a healthy digestive system.