Alimentary Canal in Humans: Structure, Functions, and More

The alimentary canal is a continuous, tube-like pathway that begins at the mouth and ends at the anus. It is primarily responsible for digesting the food we eat, absorbing nutrients, and expelling undigested material. In this article, we will explore each segment of the human alimentary canal, understand how they function together, and learn some additional facts that can aid you in remembering essential details.

Let us start by understanding why the alimentary canal organs are vital for our body:

• They break down large food particles into simpler substances.

• They help absorb nutrients into the bloodstream.

• They assist in removing undigested waste from the body.

Main Parts of the Alimentary Canal

Below are the major components of the human digestive pathway, along with their key functions:

1. Mouth and Oral Cavity

• Ingestion of Food: The digestive process begins as soon as food enters the mouth.

• Teeth: Humans have two sets of teeth (milk/deciduous and permanent). The four types of teeth are incisors (cutting), canines (tearing), premolars (chopping), and molars (grinding and chewing).

• Tongue: A muscular organ that helps mix food with saliva and rolls it into a bolus for easy swallowing. For more about its structure and types of papillae, refer to our Structure of Tongue resource.

• Palate: Forms the roof of the oral cavity and separates the mouth from the nasal passage.

2. Pharynx

• Connects the mouth to the oesophagus and also serves as a pathway for air.

• The epiglottis, a small flap of cartilage, prevents food from entering the windpipe.

3. Oesophagus

• A muscular tube that delivers swallowed food (bolus) from the pharynx to the stomach.

• The gastro-oesophageal sphincter at the end of the oesophagus regulates food entry into the stomach.

4. Stomach

• A muscular, sack-like organ located on the upper left side of the abdominal cavity.

• Divided into four regions: cardiac (near the heart), fundus (dome-shaped top), body (main central portion), and pyloric (which leads to the small intestine).

• The pyloric sphincter controls the flow of partially digested food into the small intestine.

5. Small Intestine

• The longest part of the human alimentary canal, divided into three regions:

1. Duodenum: C-shaped first portion where secretions from the liver and pancreas mix with the food.

2. Jejunum: Middle segment where most nutrient absorption takes place.

3. Ileum: Highly coiled final segment that continues absorption and leads into the large intestine.

• A helpful mnemonic for remembering the sequence is: “Don’t Jump In” (D – Duodenum, J – Jejunum, I – Ileum).

6. Large Intestine

• Receives the remaining indigestible material from the small intestine.

• Divided into three main parts:

1. Caecum: A small pouch that houses symbiotic microorganisms. The vermiform appendix, a vestigial organ in humans, is attached to the caecum.

2. Colon: Further categorised into ascending, transverse, descending, and sigmoid regions. The colon absorbs water, salts, and some vitamins.

3. Rectum: Stores faeces before they are expelled through the anus.

Additional Points to Note

• The human alimentary canal works in harmony with other systems like the human respiratory system and the human excretory system to keep the body healthy and functional.

• The liver and pancreas, though not directly part of the tube, are crucial glands that secrete enzymes and substances aiding digestion.

• Muscular contractions known as peristalsis move food along the canal.

• The epiglottis ensures a proper route for food to the oesophagus and air to the trachea, preventing choking.

Quick Quiz (With Answers)

1. Which part of the alimentary canal is responsible for most nutrient absorption?
   A. Stomach
   B. Duodenum
   C. Jejunum
   D. Rectum
   Answer: C. Jejunum

2. What is the function of the epiglottis?
   A. To crush the food into smaller pieces
   B. To help swallow the food bolus
   C. To prevent food from entering the windpipe
   D. To absorb excess water
   Answer: C. To prevent food from entering the windpipe

3. Which of these helps in the grinding and chewing of food?
   A. Canines
   B. Molars
   C. Incisors
   D. Premolars
   Answer: B. Molars

4. Where do pancreatic and bile secretions enter the alimentary canal?
   A. Stomach
   B. Duodenum
   C. Ileum
   D. Colon
   Answer: B. Duodenum

Related Topics

• Structure of Tongue

• Gastrointestinal Tract

• Human Digestive System