Alimentary Canal - Anatomy, Structure, Functions, Types

The alimentary canal is often referred to as the digestive tract. It is long, tube-like with no apparent lumen. It extends from the mouth to the anus, where digestion, absorption, and excretion occur. One of the most important points that students prepare for when approaching competitive exams like NEET, AIIMS, and other entrance tests is the comprehensive study of the alimentary canal's anatomy. Study about this topic is included in the class 11 CBSE Biology syllabus as a core part of the chapter Digestion and Absorption.

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This Story also Contains

1. What Is The Alimentary Canal?
2. Anatomy Of The Alimentary Canal
3. Parts Of The Alimentary Canal
4. Layers of the Alimentary Canal
5. Functions Of The Alimentary Canal
6. Tips, Tricks, and Strategies to Prepare for Alimentary Canal
7. Weightage of Questions from Alimentary Canal Anatomy in Different Exams
8. Types of Questions Asked on Alimentary Canal Anatomy in Different Exams
9. Recommended Video On Alimentary Canal - 'Anatomy, Structure, Functions

What Is The Alimentary Canal?

The alimentary canal is an extended, continuous, hollow tube running from the mouth to the anus. It performs the digestion of food and absorption of nutrients, with the elimination of waste. The complex system involves multiple organs and processes working in unison to ensure that the body receives proper nourishment for energy, growth, and repair.

The anatomy and functions of the alimentary canal are the keys to understanding how our bodies process the food we eat. This shall, therefore, form the basement for the students starting from Class 9 to students who are preparing for the NEET exams.

Read More:

• MCQ Practice Questions on Alimentary Canal
• Digestion and Absorption
• Diagram of Digestive System
• Structural Organisation in Animals

Anatomy Of The Alimentary Canal

The alimentary canal is about a 9-meter-long, continuous muscular tube extending from mouth to anus. It represents an important part of the digestive process, consisting of many organs that are specially differentiated regions of this Canal, working in a coordinated manner on food digestion, absorbing the released nutrients, and finally, the elimination of the remaining waste.

Those sections are the mouth, pharynx, oesophagus, stomach, small intestine, large intestine, rectum, and anus. All these sections take part in digestion and nutrient absorption to meet the organism's needs for proper functioning. An adult alimentary canal is approximately 9 meters in length.

Diagram: Alimentary Canal

Parts Of The Alimentary Canal

Each part of the alimentary canal has different structures and carries out different functions required in digestion.

Mouth

• Teeth: Aids in mechanical digestion by grinding.

• Tongue: Aids in moving food around with its movement and is covered with taste buds.

• Salivary Glands: Secrete saliva that contains an enzyme amylase.

Functions

• Ingestion: Taking food.

• Mastication: The mechanical breaking of food by chewing.

• Enzymatic Breakdown: Initial digestion of carbohydrates by salivary amylase.

Pharynx

• Oropharynx: The passageway for food.

• Nasopharynx: Part of the respiratory pathway.

• Laryngopharynx: It leads to the oesophagus.

Function

• Pathway for Food and Air: The food passes into the oesophagus and the air into the larynx.

Oesophagus

• The lining of the muscular tube is of stratified, squamous epithelium.

• The Sphincters: There is an upper oesophagal sphincter and a lower oesophagal sphincter.

Function:

• Peristalsis: Wave contractions of the muscles which propel the food towards the stomach.

• Transport: Food from the pharynx into the stomach.

Stomach

• Regions: Fundus, body, antrum, and pylorus

• Gastric Glands: Secrete hydrochloric acid and pepsinogen

Function:

• Storage: Stores swallowed food temporarily.

• Mixing: Food is churned with gastric juices and changed into chyme.

• Acid Secretion: Hydrochloric acid activates the pepsinogen into pepsin.

• Initial Protein Digestion: Pepsin breaks down protein into peptides.

Small Intestine

• Segments: Duodenum, jejunum, ileum.

• Villi and Microvilli: Increase surface area to absorb.

Functions:

• Absorption of Nutrients: Primary area for the absorption of nutrients into the bloodstream.

• Digestion: Further break down the carbohydrates, proteins, and fats.

• Surface area enhancement: The villi and microvilli maximise the efficiency of absorption.

Large Intestine

• Segments: Cecum, colon , rectum.

• Houses some friendly bacteria.

Function:

• Water Absorption: Indigestible food has water and electrolytes reabsorbed here.

• Formation of Feces: The residual waste is compacted into faeces.

• Vitamin Production: Some vitamins, such as vitamin K, are produced by bacteria.

Rectum And Anus

• Rectal Walls: There are stretch receptors that send signals that it is time to defecate.

• Anal Sphincters: There are internal ( involuntary ) and external ( voluntary ) sphincters.

Function:

• Storage: This is the final storage area for faeces until it is eliminated.

• Defecation: Controls the expulsion of faeces from the body.

Layers of the Alimentary Canal

The alimentary tract's walls share a fundamentally consistent basic structure across the whole tract. To achieve the necessary functionality, specific portions of an alimentary canal may, however, differ physically.

The human alimentary canal tract is further divided into four layers from inside to outside respectively :

• Mucosa (Innermost layer)

• Sub Mucosa

• Muscularis

• Serosa (Outermost layer)

Mucosa

The mucosal, or mucous membrane layer, is the innermost wall lining the alimentary canal lumen. Three more layers are separated from the mucous membrane Epithelium, Lamina propria - a loose connective tissue layer, and Muscularis mucosa- a smooth muscle layer.

• Different portions of the alimentary canal have differences in their fundamental structure depending on their activity and role.
• The mucosal membrane in the mouth and the anus is composed of stratified squamous tissue to protect the alimentary canal from abrasion, while the stomach and intestine have thin columnar cells in the epithelium to allow for nutrient absorption.
• The epithelium of the small intestine is folded into finger-like extensions to create a high surface area for nutrient absorption.
• In the mucus layer, epithelial tissue like goblet cells release mucus and specific digestive enzymes.

Submucosa

• The mucosal membrane is encircled by an uneven, thick layer of connective tissue that houses lymphatic vessels, nerve terminals, and blood vessels.
• The submucosal layer is made up of fibroblasts, collagen and an acellular matrix. This layer also contains certain glands, such as Brunner glands.
• The submucosa of the duodenum is the site of Brunner's glands.
• They release an alkaline fluid that contains mucin that protects the mucosa from the stomach contents' acidic influx into the duodenum.
• Muscularis This layer of smooth muscle is in charge of the peristaltic movement and segmental contractions that carry food along the alimentary canal.
• Its longitudinal muscle layer as well as the inner circular layer are the two layers in which these smooth muscles are organized.
• Between the two smooth muscle layers is a small layer of connective tissue.
• The plexus Myenteric plexus or also called as Aurbach plexus.
• It is a type of vascular connective tissue, that houses the myenteric nerve plexus.
• The motility of the digestive tract is controlled by the myenteric nerve plexus.

Serosa

• The organs located in the peritoneal cavity behind the diaphragm are covered by the serosa, a loose layer of connective tissue.
• This layer, which is made up of secretory epithelial cells, lessens friction brought on by muscle activity.

Functions Of The Alimentary Canal

The alimentary canal performs various functions that are vitally important in maintaining health and nutrition by ensuring that food is properly processed by the body for the extraction and absorption of its nutrients, and removing waste from the organism.

Ingestion

• Food and liquids are ingested into the mouth to start the digestion process. Thus, nutrients enter the body.

• The beginning of the process of digestion where food is ingested into the mouth.

Digestion

Digestion involves the physical and chemical degradation of food into smaller, absorbable constituents.

• Mechanical Digestion: Physical breakdown of food into smaller pieces as in chewing and stomach churning.

• Chemical Digestion: Enzymatic breakdown of complex molecules into simpler ones.

• Enzymes Involved: Amylase on carbohydrates, pepsin on proteins, and lipase on fats.

Absorption

• Nutrients, vitamins, and minerals are absorbed into the bloodstream mainly through the walls of the small intestine.

• Nutrients, Vitamins, Minerals: The simple substances that get absorbed to be used by the body

Mechanisms:

• Passive Diffusion: Movement of molecules from high to low, without energy

• Active Transport: Energy-dependent process to move molecules against a concentration gradient

Excretion

• This way, through defecation, indigestible substances along with waste are excreted. This ensures that nonusable constituents are expelled out of the organism.

• Excretion of Waste Products: The process of removing waste and undigested material from the body.

Tips, Tricks, and Strategies to Prepare for Alimentary Canal

Understand the alimentary canal in students for NEET, Nursing and other paramedical tests. Tips to memorize easily:

Mnemonics

M.E.S.S.I.L.R.A which begins from the Mouth, Esophagus, Stomach, Small Intestine, Large Intestine, Rectum, and Anus.

Study Aids

• Use diagrams or flowcharts to explain the structure and functions of each part.
• Divide the digestion process from mouth to anus.

Multimedia Learning

• Watch videos or animations to visualize the process.

Analogies

• Imagine the alimentary canal as a food processing factory: the mouth is the reception area, the stomach is the mixer, and the intestines process and absorb nutrients.

Paper Flashcards

• Make flashcards for words like peristalsis, bile, villi, etc, so as not to memorize them in a short time.

Weightage of Questions from Alimentary Canal Anatomy in Different Exams

The table given below indicates the weightage of the alimentary canal questions in different Exams:

Read More:

Recommended Video On Alimentary Canal - 'Anatomy, Structure, Functions