Digestive System of Earthworms

Earthworms are hermaphrodites which suggest that they each possess male and female reproductive organs. Following breeding, eggs are placed in cocoons where fertilization happens. After fertilization, the egg begins splitting. By the moment an earthworm has achieved the four celled-stage. The cell contents have been divided into various new cells. The outcome of these cells has been set and they would not be able to develop into a full creature if left to grow alone.

In this post, we will study the digestive system and investigate the roles of the related smooth muscle. The center of concern includes the gizzard.  These organs are subsequent to the esophagus, which may be clearly distinguished since it is ringed by larger blood veins that act as hearts. The crop-gizzard is also partly covered by the cream-colored seminal vesicles of the reproductive tract.

Structure of the Earthworm’s Digestive System 

The digestive system of the worm contains an alimentary canal and ducts together with the physiology of digestion.

Alimentary canal of the earthworm

The alimentary canal spans from the mouth to the anus as it is lengthy. It consists of the following parts:

1. Mouth: 1st segment

2. Buccal Cavity: 2nd-3rd section or center of the 3rd region

3. Pharynx: 3rd-4th segment

4. Oesophagus: 5th -7th segment

5. Gizzard: 8th or 8th-9th segment

6. Stomach: 9th or 10th-14th segment

7. Intestine: 15th up to the final section except the anus

8. Anus: Last segment

• Mouth: The mouth of an earthworm is a crescentic aperture situated in the 1st segment below the prostomium. The mouth leads into a buccal cavity. Ingestion of food takes place through the mouth.

• Buccal Cavity: The buccal cavity is a short, wide, and thin-walled tube extending from 2nd up to 3rd or middle of 3rd segment. It has two types of muscle; protractile muscles and retractile muscles. It protrudes out through the mouth with the help of a special muscle for holding the food particles during feeding. The buccal cavity leads into the pharynx.

• Pharynx: It is a small, swollen, wider, thick-walled pear-shaped chamber that extends till the 4th segment. It is wider than the buccal cavity and differentiated from it using constriction. It has the pharyngeal gland that is located in the dorsal salivary chamber. The pharyngeal gland is made of chromophil cells, which produce saliva containing the proteolytic enzyme; protease, and mucin which convert a protein into amino acids and make the food soft respectively.

• Oesophagus: It is a narrow thin-walled tubular structure. The esophagus extends from the 5th to the7th segment. It has no gland and passes the food particles from the pharynx to the gizzard. It leads into the gizzard.

• Gizzard: The earthworm gizzard is an oval, thick-walled, and highly muscular organ lying in the 8th or 8th-9th segment. It is the hardest part of the alimentary canal because of the presence of the inner lining of the cuticle. 

•  Stomach: The gizzard leads to a short, narrow, thin-walled, vascular tubular structure called the stomach. It extends from the 9th or 10th to the 14th segment and is wider than the esophagus. The stomach has a calciferous gland that helps in the neutralization of food by the calcification process. The stomach leads to the intestine. The glandular cells of the stomach produce proteolytic enzymes which assist in the digestion of protein.

• Intestine: The intestine is a long and thin-walled tube that extends from the 15th to the last segment except for the anus. The inner lining is ciliated, vascular, folded, and glandular. It’s the intestinal lining that is folded to form villi. One villus becomes more developed than the other and runs mid-dorsally from the 27th to the last 25th segment.

Typhlosole Divides the Intestine into 3 Regions

1. Pre-typhlosolar Region: This region extends from the 15th segment to the 26th segment so it is the first part of the intestine. It consists of villi but no typhlosole. In the 26th segment, there is a pair of short and conical lateral outgrowth called intestinal caeca that extends upward up to the 23rd segment. Intestinal caeca produce amylase that helps in starch digestion.

2. Typhlosolar Region: It is the 2nd or middle part of the intestine which extends from the 27th segment to last from the 25th segment. It has both villi and typhlosole. The typhlosole is a avascular and glandular fold that increases the absorptive surface area of the intestine.

3. Post-typhlosolar Region: It is the last part of the intestine lying in the last 23rd-25th segment in front of the anus and is also called the rectum. It lacks intestinal villi and typhlosole and contains small pellets of mud that are thrown out through the anus to form casting.

Anus: The anus is a circular opening in the last segment called the anal segment.  Undigested food materials are released through the anus in the form of worm casting.

Digestive Glands: There are 4 different types of digestive glands associated with the alimentary canal of earthworms.

1.     Pharyngeal gland

2.     Gastric gland

3.     Intestinal glands

4.     Intestinal caeca

Earthworm Digestive System Diagram 

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Physiology of Digestion

Earthworms live upon various forms of detritus and natural decomposition like decomposing leaves, microorganisms, etc. found in soil. They may eat freely on grasslands and other plants as well.

During eating the oral cavity is enlarged out with the aid of protractile and retractile muscles and the meal is brought into the mouth. The meal gets the pharynx via the buccal cavity. The dorsal chamber of the pharynx comprises the pharyngeal gland formed of chromophil cells that generate saliva including mucin and protease. Mucin lubricates the meal and changes it to soft food while protease transforms protein into amino acids. The grains subsequently move down the esophagus into the gizzard. There it is broken and squashed into the fine form owing to the compression of circular muscles of the gizzard. The ground food material enters into the stomach where the neutralization of food takes place by a calcification process. Also, the complete breakdown of protein by digestive enzymes is taken out here. Now the food particles pass into the gut. In the colon, intestinal caeca generate amylase which transforms starch into glucose.

In Intestine various enzymes are released and operate on the target as below:

1.    Protease: Converts protein into amino acid.

2.    Amylase: It transforms starch into two molecules of glucose.

3.    Cellulase: Converts cellulose into glucose

4.    Chitinase: this digests chitin in the exoskeleton of small organisms.

5.    Lipase: This enzyme transforms lipids into glycerol and fatty acids.

Digestion takes place mostly in the intestine and the digested food is absorbed by villi. Then it passes into the bloodstream through capillaries. The undigested food and the soil are released in the form of casting through the anus. 

Discovery of Digestive System

In the early 1800s, Mackinac Island in Michigan didn't sound like the most plausible location for anyone to discover how digestion functioned, yet that's precisely where Army physician Dr. William Beaumont discovered it in the year 1822. Beaumont established once and for all that stomach digestion is chemical, a product majorly of the gastric juice itself, which Beaumont correctly assumed was largely made of hydrochloric acid. The discovery catapulted the doctor into prominence.

Charles Darwin about Earthworms

Charles Darwin, a British biologist, began and completed his nearly 45-year work with investigations, tests, and hypotheses about earthworms. Earthworms are particularly susceptible to vibrations, according to Darwin. Evolutionary theory of Charles Darwin as a caricature. Following Darwin's publication of The Formation of Vegetable Mould via the Action of Worms, the graphic was featured in a Punch almanac. Darwin was intrigued by the idea that such insignificant organisms may be intelligent. Their movement through the earth agitates the soil, and the inherent chemistry of their intestines converts dirt and plant debris into fertile granules, he learned.

Initial Appearance of Earthworms

A worm-like organism that lived on the seafloor more than 500 million years ago may have played a crucial role in the creation of the animal world. The organism, which is roughly the size of a grain of rice, is characterized as the oldest specimen of a bilaterian ever discovered in fossil evidence.

Intestines of the Earth

Earthworms, which Aristotle referred to as the "intestines of the earth," are vital soil creatures that contribute to the breakdown of plant residues, such as the thatch covering, and the recycling of minerals. In their intestines, they aid in the breakdown and conditioning of plant leftovers.

Breathing Process in Worms

Worms, like humans, breathe in oxygen and exhale carbon dioxide, but they lack lungs. They can't breathe through their mouths, and they can't breathe through their noses either because they don't have any.  They inhale and exhale through their skin. Because air breaks into their skin's mucus, they must keep moist in order to breathe. Worms suffocate if they become too dry. Fresh oxygen is pulled via the epidermis into the worm's circulatory system, and the worm's hearts transfer oxygenated blood to the brain. The worm's movements cause blood to flow to the complete parts of the body, where it is pumped forward by the heart. Carbon dioxide is released from the bloodstream and returns to the skin.

Do Worms Have Brains?

Yes, however, they aren't very complicated. The brain of each worm lies among its other organs, connecting nerves from the worm's epidermis and muscles to govern all of its feelings and movements.

How much DNA do we share with Worms?

Based on a new study reported in the journal Nature, a team of worldwide scientists discovered that human beings share almost 70% of their genome with acorn worms.

How do Earthworms Reproduce?

Each earthworm's male and female sexual parts can generate sperm and eggs, correspondingly. Despite the fact that earthworms are hermaphrodites, they require a partner to breed. Two worms position along inverted from each other while mating to transfer sperms. Young worms then develop from the fertilized eggs.