The Human Digestive System and The Alimentary Canal

Subject :


Topic :

Digestive System

Animals Alimentary Canal

Class :


Term :

First Term

Week :

Week 1

Educational Teaching Aids:

  • Footage of Digestive system of animal
  • Pattern alimentary canal of animal


Reference Materials 

  • Scheme of Work
  • On-line Info
  • Textbooks
  • Workbooks

Earlier Instructions:

The pupils have earlier information of dwelling issues and non dwelling issues



Behavioural Goals :  On the finish of the lesson, the learners will be capable to

  1. Clarify the digestive system
  2. Point out sorts of alimentary tracts in animals
  3. Listing out the elements of human digestive system


Content material :


  1. Definition of Digestive System, Digestion and Alimentary Canal
  2. Kinds of Alimentary Tract
  3. Elements of the Mammalian Alimentary Canal
  4. The Human Digestive System
  5. 4-Chambered Abdomen


Definition of Digestive System

The digestive system is a sequence of related organs whose objective is to interrupt down, or digest, the meals we eat. It is the totality of all the organs that are involved in the breaking down of food that we eat so that energy will be released.. Meals is made up of huge, advanced molecules, which the digestive system breaks down into smaller, easy molecules that may be absorbed into the bloodstream. The easy molecules journey by means of the bloodstream to all the physique’s cells, which use them for progress, restore, and vitality.

All animals have a digestive system, a function that distinguishes them from vegetation. Crops produce their very own meals in a course of known as photosynthesis, throughout which they use daylight to transform water and carbon dioxide into easy sugars. However animals, together with people, should absorb meals within the type of natural matter, reminiscent of vegetation or different animals.



Meaning of Digestion

Digestion is the breaking down of complicated meals substances or particulars into easy, soluble and diffusible type by mechanical and chemical means.



Digestion usually includes two phases: a mechanical part and a chemical part. Within the mechanical part, enamel or different constructions bodily break down giant items of meals into smaller items. Within the chemical part, digestive chemical substances known as enzymes break aside particular person molecules of meals to yield molecules that may be absorbed and distributed all through the physique. These enzymes are secreted (produced and launched) by glands within the physique.



Definition of Alimentary Canal

This can be a tubular passage between the mouth and the anus, together with the organs by means of which meals passes for digestion and elimination as waste. The alimentary canal can also be known as the digestive tract or intestine.

In most holozoic animals, digestion and absorption of meals happen within the alimentary canal or intestine. A easy unicellular animal doesn’t have an alimentary canal.


Kinds of Alimentary Tract

There are several types of alimentary tracts in animals. Nevertheless, there isn’t any particular alimentary canal in plant. This contains:

  1. Intracellular alimentary tract: This can be a digestion that takes place contained in the cell, inside a meals vacuole.g. unicellular organism like amoeba
  2. Extracellular alimentary tract: This can be a sort of digestion that happen in multi-cellular organisms. The mouth opens right into a sac-like intestine cavity the place meals is digested. E.g. Hydra.
  3. Easy alimentary tract for easy digestion of meals. E.g. Birds.
  4. Compartmentalized alimentary tract by ruminants for digestion of cellulose. E.g. ruminants like cow.
  5. Complicated Human alimentary tract; an extended tube stretching from the mouth to the anus. Most of it’s coiled up within the belly cavity. It’s divided into a number of areas: mouth, oesophagus, abdomen, and intestines. Every area performs a task within the digestion and/or absorption of meals.



Elements of the Mammalian Alimentary Canal

A typical mammalian alimentary canal consists of the next elements, specifically: mouth, pharynx, oesophagus, abdomen, small gut, rectum and anus. All these elements might be present in most vertebrates. Nevertheless, there are modifications of the elements of the alimentary canal in numerous, animals. In some animals, a construction could also be diminished or enlarged, whereas in others, some elements could also be absent. The modifications mirror the varied modes of feeding and sorts of weight loss program.



Description and Capabilities of the Elements of the Mammalian Alimentary Canal


Mouth and Tooth

In greater animals particularly in human, the incisors, canines, premolar and molar are enamel used to masticate the meals into particles which expose it to giant floor space for the motion of the enzymes. Digestion begins within the mouth.



The tongue tastes the meals, helps within the motion of the meals within the mouth to permit turning and mixing of the meals with saliva and in forming meals into bolus to permit swallowing.



The saliva lubricates the meals, permits simple chewing or motion of meals within the mouth for swallowing, varieties solvent for meals, accommodates enzyme-ptyalin which digests cooked starch to maltose and is barely alkaline which is medium for motion of ptyalin. The chewed meals within the mouth is then swallowed.



It’s subsequent to the mouth. In some animals, such because the earthworm and Planaria, it’s muscular. In man it’s brief and extensive. The pharynx results in the trachea and the oesophagus. It’s used for passing meals supplies into the oesophagus or gullet.



This can be a slim, straight, lengthy, tube passing by means of the thoracic area and the diaphragm into the abdomen. Digestion doesn’t happen right here. However it’s used for passing meals substances into the abdomen by a wave-like muscular contraction and leisure known as peristalsis. This kind of motion happens all through the human alimentary canal. Chewed meals is handed to the abdomen by peristaltic motion of the oesophagus.


In some animals, the decrease a part of the oesophagus could also be modified to type the crop as in bugs and birds. These are storage organs for the meals consumed.


The abdomen is primarily a storage organ. However in most mammals, it is rather muscular and digestion continues in it. In birds, bugs and grasshopper and earthworm, the abdomen modified right into a grinding organ known as gizzard. The gizzard is generally muscular with small sharp stones which masticate the meals earlier than it’s additional digested within the gut. Therefore, gizzard is possessed by some vertebrates e.g. birds and a few invertebrates e.g. bugs and earthworms which lack enamel of their mouth. Ruminants abdomen are modified into 4 chambered or compartments specifically rumen, reticulum, psalterium and abomasums.

The abdomen, situated within the higher stomach just under the diaphragm, is a saclike construction with robust, muscular partitions. The abdomen can increase considerably to retailer all of the meals from a meal for each mechanical and chemical processing. The abdomen contracts about 3 times per minute, churning the meals and mixing it with gastric juice. This fluid, secreted by 1000’s of gastric glands within the lining of the abdomen, consists of water, hydrochloric acid, an enzyme known as pepsin, and mucin (the principle part of mucus). Hydrochloric acid creates the acidic surroundings that pepsin wants to start breaking down proteins. It additionally kills microorganisms which will have been ingested within the meals. Mucin coats the abdomen, defending it from the results of the acid and pepsin. About 4 hours or much less after a meal, meals processed by the abdomen, known as chyme, begins passing a bit at a time by means of the pyloric sphincter into the duodenum, the primary portion of the small gut.



In human, the wall of the abdomen secretes gastric juice.  This accommodates hydrochloric acid which prevents the meals within the abdomen from being decay and two enzymes-rennin and pepsin. Rennin curdles milk, whereas pepsin converts protein within the meals into peptones. Meals could stay within the abdomen for 3-4hours on the finish it’s transformed to a semi-liquid paste known as chyme. Be aware that meals is regulated into the abdomen from the gullet by a muscle known as cardiac sphincter, whereas chyme is regulated to the small gut by one other muscle known as pyloric sphincter.

The Small Gut

Most digestion, as properly as absorption of digested meals, happens within the small gut. This slim, twisting tube, about 2.5 cm (1 in) in diameter, fills a lot of the decrease stomach, extending about 6 m (20 ft) in size. Over a interval of three to 6 hours, peristalsis strikes chyme by means of the duodenum (first part of the small gut) into the subsequent portion of the small gut, the jejunum, and at last into the ileum, the final part of the small gut.

A watery residue of indigestible meals and digestive juices stays unabsorbed. This residue leaves the ileum of the small gut and strikes by peristalsis into the massive gut, the place it spends 12 to 24 hours. The big gut varieties an inverted U over the coils of the small gut. It begins on the decrease right-hand facet of the physique and ends on the decrease left-hand facet. The big gut is 1.5 to 1.8 m (5 to six ft) lengthy and about 6 cm (2.5 in) in diameter.

Throughout this time, the liver secretes bile into the small gut by means of the bile duct. Bile breaks giant fats globules into small droplets, which enzymes within the small gut can act upon. Pancreatic juice, secreted by the pancreas, enters the small gut by means of the pancreatic duct. Pancreatic juice accommodates enzymes that break down sugars and starches into easy sugars, fat into fatty acids and glycerol, and proteins into amino acids. Glands within the intestinal partitions secrete further enzymes that break down starches and complicated sugars into vitamins that the gut absorbs. Constructions known as Brunner’s glands secrete mucus to guard the intestinal partitions from the acid results of digestive juices.

The small gut’s capability for absorption is elevated by hundreds of thousands of finger-like projections known as villi, which line the inside partitions of the small gut. Every villus is about 0.5 to 1.5 mm (0.02 to 0.06 in) lengthy and lined with a single layer of cells. Even tinier finger-like projections known as microvilli cowl the cell surfaces. This mixture of villi and microvilli will increase the floor space of the small gut’s lining by about 150 instances, multiplying its capability for absorption. Beneath the villi’s single layer of cells are capillaries (tiny vessels) of the bloodstream and the lymphatic system. These capillaries enable vitamins produced by digestion to journey to the cells of the physique. Easy sugars and amino acids cross by means of the capillaries to enter the bloodstream. Fatty acids and glycerol cross by means of to the lymphatic system.

The Giant Gut

The giant gut serves a number of necessary features, specifically:

  1. It absorbs water: About 6 liters (1.6 gallons) every day—in addition to dissolve salts from the residue handed on by the small gut.
  2. As well as, micro organism within the giant gut promote the breakdown of undigested supplies and make a number of nutritional vitamins, notably vitamin Ok, which the physique wants for blood clotting.
  3. The big gut strikes its remaining contents towards the rectum, which makes up the ultimate 15 to twenty cm (6 to eight in) of the alimentary canal. The rectum shops the faeces—waste materials that consists largely of undigested meals, digestive juices, micro organism, and mucus—till elimination. Then, muscle contractions within the partitions of the rectum push the faeces towards the anus. When sphincters between the rectum and anus chill out, the faeces cross out of the physique.

A Part of the Giant Gut

The Human Digestive System

The human digestive system consists of a sequence of organs and constructions that assist break down meals and take up vitamins to be used all through the physique. Meals enters the digestive system by means of the mouth and passes by means of the oesophagus, abdomen, small gut, giant gut, and rectum. Different organs, such because the liver, additional assist within the breakdown of meals, absorption of vitamins, and elimination of indigestible supplies from the physique.

4-Chambered Abdomen

Ruminant animals, together with sheep, home cattle, goats, deer, and giraffes, have four-chambered stomachs.




The subject is offered step-by-step


Step 1:

The category trainer revises the earlier matters


Step 2.

He introduces the brand new subject


Step 3:

The category trainer permits the pupils to present their very own examples and he corrects them when the wants come up



Conclusion :


The category trainer wraps up or conclude the lesson by giving out brief observe to summarize the subject that she or he has simply taught.

The category trainer additionally goes spherical to guarantee that the notes are properly copied or properly written by the pupils.

She or he does the required corrections when and the place  the wants come up.



  1. Outline digestive system.
  2. Outline digestion.
  3. Clarify the sorts of alimentary tract.
  4. Describe the elements and features of the mammalian alimentary canal.