Parts of Earthworm Digestive System in Order

In this parts of earthworm digestive system in order post we have briefly explained about earthworm digestive system organs (Mouth: 1st segment, Buccal Cavity: 2nd-3rd segment or middle of 3rd segment, Pharynx: 3rd-4th segment, Oesophagus: 5th -7th segment, Gizzard: 8th or 8th-9th segment, Stomach: 9th or 10th-14th segment, Intestine: 15th up to the last segment except for anus, and Anus: Last segment.

Earthworm digestive system organs comprises an alimentary canal that runs along the length of the body from mouth to anus and glands.  Functionally regionated into various parts i.e. mouth and buccal chamber, pharynx, esophagus, gizzard stomach, and intestine. 

Digestive System of Earthworms and Physiology of Digestion

Earthworm Digestive System Organs

Parts of Earthworm Digestive System Organs

1. Mouth

The mouth of an earthworm digestive system organs is a crescentic aperture located below the prostomium in the first segment. A buccal cavity is formed by the mouth. Food is chewed and swallowed through the mouth.

2. Buccal Cavity

The buccal cavity an earthworm digestive system organs is a short, wide tube with a thin wall that extends from the 2nd to the 3rd segment or the middle of the 3rd segment. Protractile muscles and retractile muscles are the two types of muscles found in it. It protrudes into the mouth with the assistance of a specific muscle for the purpose of retaining food particles during feeding. The pharynx is reached through the buccal cavity.

3. Pharynx

Pharynx of earthworm digestive system organs is a little, enlarged, broader, thick-walled pear-shaped chamber that stretches all the way to the fourth segment. It’s wider than the buccal cavity and can be distinguished by constriction. The pharyngeal gland, which is found in the dorsal salivary chamber, is present. The pharyngeal gland is made up of chromophil cells that generate saliva containing proteolytic enzymes like protease and mucin, which break down proteins into amino acids and soften meals.

4. Oesophagus

Oesophagus of earthworm digestive system organs is a tubular structure with a thin wall. From the 5th to the 7th segment, the oesophagus is located. It lacks a gland and is responsible for passing food particles from the throat to the gizzard. It is connected to the gizzard.

5. Gizzard

The gizzard of earthworm digestive system organs is an oval, thick-walled, extremely muscular organ located in the 8th or 8th-9th segment. Because to the existence of the cuticle’s inner layer, it is the most difficult region of the alimentary canal.

6. Stomach

The stomach of an earthworm digestive system organs extends from 9-14 segments. It’s a tubular and vascularized structure. The segment 10-12 has three pairs of calciferous glands, which create lime carbonate and aid in the neutralisation of humic acid in the humus. Proteolytic enzymes are secreted by glandular cells in the stomach, which aid in protein digestion. The intestine is connected to the stomach.

7. Intestine

Except for the anus of earthworm digestive system organs, the intestine is a lengthy, thin-walled tube that runs from the 15th to the last segment. The inner lining is glandular, ciliated, vascular, and folded. The villi are formed when the gut lining is folded. From the 27th to the last 25th segment, one villus gets more developed than the other and runs mid-dorsally. The effective area of absorption in the intestine is increased by these villi. There are three sections to the intestine:

Pre-typhlosolar region: present from the 15th to the 26th segment It has villi in it. On the 26th segment, there is a small conical projection known as the intestinal caeca. The amylase enzyme is secreted by the intestinal caeca, which stretch upwards to the 23rd segment. Amylase is a digestive enzyme that aids in the digestion of carbohydrates.

Typhlosolar region: The typohlosolar area of an earthworm digestive system organs is the vast internal median fold of the dorsal wall of the intestine that forms a longitudinal ridge after the 26th segment, with the exception of the last 23rd-25th segments. Typhlosole increases the absorption surface area in the gut.

Post-typhlosolar region: The post-typhlosolar area of an earthworm digestive system organs, often known as the rectum, is the last 25 segments of the intestine. This region lacks intestinal villi and typhlosole. It leads to the anus and stores faecal pellets.

8. Anus

In the last segment, there is a little round aperture. The anus of an earthworm digestive system organs is the opening to the outside of an earthworm’s alimentary canal. Undigested food is expelled in the form of worm casting through the anal orifice.

9. Digestive Glands

There are 4 different types of digestive glands associated with the alimentary canal of earthworm digestive system organs.

Pharyngeal gland

Gastric gland

Intestinal glands

Intestinal caeca

Physiology of Digestion

Earthworms eat many kinds of waste and organic humus in the soil, including decaying leaves, bacteria, and other microorganisms. They can also eat grasses and other vegetation directly.

The food is dragged into the mouth when the buccal cavity is protruded out with the help of protractile and retractile muscle during feeding. Through the buccal cavity, food enters the pharynx. The pharyngeal gland, which is made up of chromophil cells and generates saliva containing mucin and protease, is located in the dorsal chamber of the pharynx.

Mucin lubricates and softens food, while protease breaks down protein into amino acids. The food particles move via the oesophagus and into the gizzard, where they are ground and crushed into a fine powder by the contraction of the gizzard’s circular muscles. 

The ground food item is absorbed into the stomach, where it is neutralised through a calcification process. Also carried out here is the thorough digestion of protein by proteolytic enzymes. The food particles now make their way into the intestine. Intestinal caeca produce amylase, which transforms starch to glucose in the intestine. 

In Intestine several enzymes are secreted and act on the substrate as follows: Protease: Converts protein into amino acid, Amylase: Converts starch into two molecules of glucose i.e. maltose, Cellulase: Converts cellulose into glucose, Chitinase: Digest chitin of exoskeleton of insects and Lipase: This enzyme converts fats into glycerol and fatty acids.

Further Readings

Reference

  1. Kotpal RL. 2017. Modern Text Book of Zoology- Invertebrates. 11th Edition. Rastogi Publications.
  2. Jordan EL and Verma PS. 2018. Invertebrate Zoology. 14th Edition. S Chand Publishing.