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Alimentary Canal- Human digestive system

Alimentary canal is the major component of our digestive system. This blog provides you with precise and up to the mark information about alimentary canal.

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Posted by Mahak Jain, 8/2/2021
Alimentary Canal- Human digestive system

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Alimentary canal is the major component of our digestive system. It starts from mouth anteriorly and opens posteriorly through anus.

So, alimentary canal is simply —

                     Mouth → Anus

Mouth leads to oral cavity , in which two important structures are present, which are tongue and teeth.

Contents of alimentary canal

  • Dentition in humans
  • Types of permanent teeth
  • Tongue
  • Pharynx
  • Oesophagus
  • Stomach
  • Small Intestine
  • Large Intestine

Dentition in humans

Dentition means the arrangement of teeth in the oral cavity.

So, in humans the two major characteristics of dentition are:

  • Thecodont :  it means, each tooth is embedded in socket of jaw bone .
  • Diphyodont : Two sets of teeth, first temporary and then permanent are formed in humans in their whole life time.     

Permanent teeth are 32 in number.

Types of permanent teeth

  1. Incisors
  2. Canines
  3. Premolars
  4. Molars

Dental formula for humans —: 2123/2123

It means , each quadrant of oral cavity contains

  • two incisors
  • one canine
  • two premolars
  • three molars

A simple pneumonic to remember the order of teeth is:

‘I’ll See Prime Minister’

In which,

I’ll – incisor

See- Canine

Prime- permolar

Minister- Molar.

Teeth are the hardest part of the body, so it’s interesting to know that which substance makes it hardest, and the answer for this is enamel.

Enamel: It is the hard chewing surface of teeth which helps in mastication.

human alimentary canal diagram

Tongue

It is the another important structure present in oral cavity. It is a freely movable muscular organ which is attached to the floor of oral cavity with the help of frenulum.

         There is presence of papillae on the surface of tongue, among which some of them also contain taste buds, and because of these taste buds only we are able to enjoy our food of different varieties having different tastes.

Pharynx

This is the another structure of alimentary canal in which oral cavity opens up. Pharynx is the common passage for food and air.

Parts of pharynx:

  1. Nasopharynx
  2. Oropharynx
  3. Hypopharynx

Now the thing which may be confusing here is, that why not food enters into the wind pipe, so the structure which prevents the entry of food in wind pipe is epiglottis. It is a cartilaginous structure which closes the wind pipe while swallowing the food.

Oesophagus

Oesophagus is commonly called as food pipe of the body. It is one of the most important part of alimentary canal because this is the only structure which takes our eaten food from pharynx to the stomach. It is approximately 25 cm long.

Stomach

Oesophagus ultimately opens up in the stomach which is a ‘J’ shaped bag like structure where the the food stays for a longer time. It contains many types of glands among which some of them secrete HCL which helps in killing of many pathogens present in the food. Many glands secrete some enzymes also which helps in digestion of food.

Parts of stomach :

  1. Cardiac- into which oesophagus opens up.
  2. Fundus- upper portion adjacent to cardiac.
  3. Body- Main central organ.
  4. Pelorus- opens up into the duodenum of small intestine.

The entry and exit of food in stomach is guarded by the gates present at these points. These gates are called sphincters.

There are two types of sphincters:

  1. Gastrooesophageal (guards entry of food)
  2. Pyloric (guards exit of food)

Small intestine

Food after getting out of the stomach enters into small intestine where most of the absorption of our food takes place. It is the longest section of alimentary canal.

Small intestine is divided into three parts:

  1. Duodenum (‘C’ shaped)
  2. Jejunum (long coiled)
  3. Ileum ( highly coiled)

It is surprising to know that, length of our small intestine is approximately 7 meters ,then how our body is able to accommodate such a large size. So this possible due to highly coiled structure of small intestine which acquires much lesser space.

Large intestine

Small intestine (ileum) further continues into the large intestine.

The reason these two parts of intestine are named ‘small’ and ‘large’ is not due to their length but due to their diameter. Large intestine is shorter than the small intestine in length.

It has three parts:

  1. Caecum
  2. Colon
  3. Rectum

Caecum is further divided into :

  1. Ascending colon
  2. Transverse colon
  3. Descending colon
  4. Sigmoid colon

Caecum is a small blind sac which hosts some symbiotic microbes which helps in digestion of food. It finally opens up into the colon.

Talking about caecum is always incomplete without knowing vermiform appendix. It is a vestigial organ that means it is no longer in use for humans but still present in our body. It is believed that soon it will be vanished off from the human race by the evolution in coming time.

A very common disease named as ‘appendicitis’ is related to vermiform appendix only, which means inflammation of this organ.

      Caecum opens up into the colon.

Food after passing through all four parts of colon reaches  to rectum which has two sphincters- one voluntary and another involuntary sphincter which regulate the passage of faeces out of the body through anal orifice.

So finally, to sum up the alimentary canal, the structures in sequence are:

  1. Oral cavity
  2. Pharynx
  3. Oesophagus
  4. Stomach
  5. Duodenum
  6. Jejunum
  7. Ileum
  8. Caecum
  9. Ascending colon
  10. Transverse colon
  11. Descending colon
  12. Sigmoid colon
  13. Rectum
  14. Anus

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