Digestive System-Earthworm, Cockroach and Frog

Digestive System-Earthworm, Cockroach and Frog

Morphology is a part of a biological study that deals with the form and structure of living organisms. It primarily deals with the structure of how living organisms sustain themselves in terms of respiration, digestion and other life components. The animal morphology differs variedly from plant morphology. Furthermore, Most animal species have different structural changes when compared with other animals. 

Digestive System of an Earthworm, Cockroach and Frog

The digestive system of Earthworm, Cockroach and frogs is very different as these species come from three different families in the animal kingdom. The digestive system of these animals are described as follows –

Digestive System of an Earthworm

The Digestive System of the Earthworm is divided into alimentary canals and different glands which helps in the digestion process. The different segments of the alimentary are – 

•  Mouth: It is the 1st segment of the alimentary canal. Ingestion takes place from this segment
• Buccal Cavity: It comprises the 2nd and 3rd segment in the alimentary canal. It is a muscular part of the digestive system of the earthworm responsible for holding the food during the feeding process
•  Pharynx: It is made of the 3rd and 4th segment in the alimentary canal. This segment consists of the pharyngeal gland which releases saliva containing proteolytic enzymes which makes the food softer
•  Esophagus: This segment is a long tube that connects the pharynx to the gizzard
•  Gizzard: Made of the 8th and 9th segment, The gizzard is the hardest muscular organ inside the earthworm which helps to push the food slowly into the stomach
•  Stomach: The stomach region starts from the 10th segment. The stomach is the most important part of the digestion process. The majority of the enzymes are mixed with the food inside the stomach. The stomach consists of a calciferous gland that helps in the calcification of food. Proteolytic enzymes are produced by the glandular cells of the stomach, which aid in protein digestion
•  Intestine: It comprises the 15th up to the last segment except for the anus. The intestine releases various enzymes which help in breaking down starch and other useful molecules for the earthworm
• Anus: It is the last segment of the earthworms where undigested food is expelled from the body

Digestive System and Process of Digestion in Pheretima

The food is dragged into the mouth. Food enters the pharynx via the buccal cavity. The pharyngeal gland is located in the dorsal chamber of the pharynx. It is made up of chromophil cells and produces saliva containing mucin and protease. 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. The protein is also digested using proteolytic enzymes. The food particles now make their way into the intestine. Intestinal caeca produce amylase, which transforms starch into glucose in the intestine. The rest of the undigested matter is expelled out the anus.

The Digestive System of Cockroaches

A cockroach is a species that is omnivorous i.e it can eat both plant and animal-based food. The Digestive System consists of the alimentary canal which can be divided into 3 parts, Foregut, Midgut and Hindgut.

The mouth opens into a short tubular pharynx, which passes and bends into a narrow tubular passage called esophagus

. Oesophagus opens into a sac-like structure called crop. 

The crop is followed by a gizzard or proventriculus. It has an outer thick layer of circular muscles and a thick, inner cutiole forming six highly chitinous plates called teeth. 

Gizzard is designed in such a manner that it helps in grinding the hard particles. The entire foregut is lined with cuticles.

A ring of blind caeca (eight in number) called enteric or hepatic caeca which secrete digestive juice is present at the junction of foregut and midgut. 

At the junction of midgut and hindgut, there is a ring of about 150 thin yellowish Malpighian tubules, which help in excretion.

 The hindgut is slightly bordered by the midgut and is lined internally by cuticles. It opens by an anus, lying posteriorly below the 10th tergum.

There is a pair of salivary glands in the thorax, one on each side of the crop. The salivary glands secrete saliva into the pharynx. The digestive juices are also produced by the wall of midgut (mesenteron) and hepatic caeca.

Digestive System of a Frog 

Digestive System.  Frog is a carnivorous animal, therefore its alimentary canal is short in  length. It consists of a bucco- pharyngeal cavity, esophagus, stomach, small intestine (duodenum and ileum) rectum and cloaca.

The mouth is present as a terminal, wide opening. It opens into a bucco – pharyngeal cavity.

There are present openings of eustachian tube, vocal sac (only in male), gullet and glottis are present in the bucco – pharyngeal cavity.

The gullet opens in a narrow and short tube like an esophagus which continues in a large and distended stomach. 

The wall of the stomach is thick, but quite distensible due to several internal longitudinal folds. It helps in converting the food into chyme and secretes gastric juice containing HCl and proteolytic enzymes. Stomach is followed by a coiled small intestine. The intestinal wall has numerous finger- like folds, called villi and microvilli, protecting into its lumen to enhance surface area of absorption for digested food.

 The first part of the small intestine lying parallel to the stomach is called duodenum. 

The duodenum is followed by a coiled ileum. Small intestine continues into a wider rectum, which opens into a cloaca. 

The urinary bladder opens into the cloaca chamber through the ureter. The cloaca opens externally by a cloacal aperture. The aperture serves both as an anus and as urogenital pore.

The digestive glands include gastric glands, intestinal glands, liver and pancreas. The gastric and intestinal glands occur in the walls of stomach and intestine, respectively. 

The liver secretes bile, which is temporarily stored in gallbladder, before being released into the duodenum. Bile does not contain any digestive enzyme however, it helps in digestion of food by changing its pH from acidic to alkaline and by emulsifying the fat. 

Pancreas is an irregular, elongated gland, situated in a mesentery and lies parallel to the stomach. It produces pancreatic juice coating digestive enzymes like trypsin, amylopsin etc.

Digestive Process of a Frog

When an insect approaches, it opens its mouth and suddenly flicks its sticky tongue out, striking its victim. When the prey comes into touch with the tongue, it rapidly attaches to it. Now the tongue is retracted into the buccal cavity.

The prey will be unable to escape once trapped in the buccal cavity. The pharyngeal wall contracts, pushing the food into the oesophagus from the buccal cavity. From this cavity different enzymes start to secrete on the food .However, because they are not active until they reach the stomach, digestion does not take place. The mucus turns the active food inactive and mushy, making it simpler to pass through. When the food reaches the stomach, gastric glands secrete gastric juice which comprises large quantities of water, the inactive pepsinogen enzyme and free hydrochloric acid. Inactive pepsinogen, upon being mixed with hydrochloric acid, changes into active pepsin. 

The acid is functional in preventing bacterial decomposition and dissolving inorganic salts, making the food softer. Pepsin of the stomach and the oesophagus act on the proteins of food and change into peptones and proteases. After this process, the fats are disintegrated inside the intestines and the leftover part is excreted from the body via the anus.

Conclusion

The digestive system of Earthworm, Cockroach and frogs is very different as these species come from three different families in the animal kingdom.Frog is a carnivorous animal, therefore its alimentary canal is short in  length. It consists of a bucco- pharyngeal cavity, esophagus, stomach, small intestine (duodenum and ileum) rectum and cloaca.Digestive System consists of the alimentary canal which can be divided into 3 parts, Foregut, Midgut and Hindgut.The Digestive System of the Earthworm is divided into alimentary canals and different glands which helps in the digestion process.