Earthworm’s Digestive System

The whole body of an earthworm is segmented, even including its digestive system. The digestive system of an earthworm is partitioned into many regions, each provided with a certain function. The food of earthworms such as soil enters the earthworm’s mouth from where it is swallowed by the pharynx. 

Then the swallowed soil passes through the second part of the digestive tract oesophagus, which comprises calciferous glands that release calcium carbonate to protect the earthworm’s body from excess calcium. In the next step after it passes through the oesophagus, the food slowly moves into the crop where it is stored, and then at a particular time, it eventually starts to move into the gizzard. 

In The gizzard, there are some particular uses of stones that the earthworm eats separately to grind the food completely. The ground food from the Grizzard then moves into the intestines, there are gland cells present in the intestine, these gland cells release fluids to aid in the digestive process. And lastly, The intestinal wall contains blood vessels, whose work is to digest the food that is absorbed and transport it to the rest of the body. 

Structure of the Earthworm’s Digestive System 

A.Mouth and buccal chamber :

• Consists of a Crescentic aperture situated on the ventral side of the prostomium.
• The mouth leads into a short, narrow,  protrusible buccal chamber with thin walls.
• the chamber lengths up to the middle of 3 segments.
• The buccal cavity is folded in shape and surrounded by muscular strands.

B.Pharynx

• It is Followed by a buccal chamber.
• Later it Extends up to the 4th segment of the body.
• The pharynx is a Pear-shaped broad and muscular that is separated from the buccal cavity by a groove.
• The roof of the pharynx is thick and projected into the pharyngeal bulb.
• Pharyngeal project lateral walls internally form narrow horizontal shelves.
• The roof of the pharynx is lined by the ciliated epithelium.
• There are Many muscles present with connective tissues and blood vessels present above the epithelium.
• Outside these muscles, there are salivary glands present.
• Glands are small in size with whitish unicellular glands of chromophil cells.
• Glands open through fine ducts.
• Glands secrete mucus for lubrication of food 
• Proteolytic enzymes for digestion of proteins.

C.Oesophagus or Gullet

• These are Lined behind the pharynx.
• Are Short, narrow, thin-walled in properties?
• Running up to 8th segments.
• Oesophagus or gullet walls are folded internally and deprived of any glands.

D.Gizzard

• This is just the modification of the oesophagus into the prominent, hard, and thick-walled muscular organ.
• This lies in the 8th or 9th segments.
• The wall of the gizzard consists of circular muscles lined by the columnar cells.
• Columnar cells are further lined by the tough cuticles.
• The function is to grind foods into a fine state with a heap of stones.

E.Stomach

• It is a type of gizzard followed by a short, narrow, and thin-walled tube.
• The stomach Extends up to the 14th segment.
• Also known as an anterior and posterior opening sphincter.
• Walls are very highly vascular and glandular but less muscular.
• Internal walls of the stomach folded transversely.
• The epithelial lining consists of glandular cells and some calciferous glands.
• Glandular cells present in the stomach secrete a proteolytic enzyme.
• Calciferous glands secrete calcium and CO2.
• Calcium neutralises the contents present in the alimentary canal.
• Calciferous glands are excretory organs that remove ions of calcium and carbonates from the blood.
• Calcite is excreted into the stomach when there is an increase in the level of ions and passed out with mud through the anus.

F. Intestines

• The intestines are the region just next to the stomach.
• These are Long, wide, and thin-walled tubes.
• Extends from the 15th segment to the anus.
• Beaded in appearance due to circular constriction and corresponding to septa.
• The internal lining of the Intestines has ciliated and glandular cells.
• The internal lining is folded to form villi.

Typhlosole Divides the Intestine into 3 Regions

These 3 regions play a vital role in the earthworm digestive system

1. Pre-typhlosolar Region: This region of the alimentary canal extends from the 15th segment to the 26th segment so it is considered the first part of the intestine. It consists of villi but no typhlosole. 
2. Typhlosolar Region: It is the 2nd or middle part of the intestine present in the alimentary canal which extends from the 27th segment to last from the 25th segment. It consists of both villi and a typhlosole.
3. Post-typhlosolar Region: In the Intestine ,the last part lies in the last 23rd-25th segment in front of the anus and this region is also called the rectum.

Physiology of Digestion 

Earthworms comprise a hydrostatic skeleton, so it lives upon various forms of decomposition and natural detritus like decomposing leaves, microorganisms, and other organisms found in soil. Earthworms may eat freely on any particular grasslands and other plants as well. During this eating process, their oral cavity is enlarged with the continuous aid of approaching and grapnel muscles, and the meal is then brought into the mouth. 

The meal gets into the pharynx via the buccal cavity. In the pharynx, the dorsal chamber comprises the pharyngeal gland which is formed of chromophil cells that are responsible for generating saliva including mucin and protease.

Conclusion

The phylum Annelida includes earthworms, which are invertebrates. They live in soil & help to make it fertile. They eat decomposing organic stuff. The typical earthworms found in India are Pheritima & Lumbricus. 

Earthworms have a long, cylindrical, segmented body and are hermaphrodites. The earthworm’s digestive system consists of an alimentary canal which runs the length of the body from mouth to the anus, as well as glands.