Class 11
Digestive system of Frog
The digestive system of frog consists of organs, which are concerned, with capturing of food (ingestion), absorption with the help of certain enzymes, absorption of the digested food, and finally removal of the waste food. Hence, digestive system is divided into 3 headings.
(i) Alimentary canal (ii) Digestive gland (iii) Physiology of digestion
Alimentary canal:- it is long, coiled tube which starts from mouth to anus (cloacal aperture). It consists of following organs
Buccopharyngeal cavity
The buccal cavity and pharynx together is called bucco-pharyngeal cavity. Buccopharyngeal cavity lies between upper jaw and lower jaws. Upper jaw is immovable but lower jaw is movable.
Teeth – there are two types of teeth. Maxillary teeth- they are found in upper jaw. They are polyphyodant (replaceable teeth) and homodont (all teeth are similar in size). Vomerine teeth- they are present on either side of roof buccopharyngeal cavity. They help to capture prey and prevent the captured pre from slipping out.
Tongue: It is thick, fleshy, and muscular and bifurcated (bifid). The tongue is protrusible i.e. tongue can be thrown out and retracted. It arises from in front of lower jaw. The tongue secrets a kind of sticky substance so that insects or prey coming neat sticks in tongue.
Vocal sac: In male frog on either side of the tongue on the lower jaw there are two pores called vocal sacs, which produce croaking sound.
Pharynx: Posterior part of buccopharyngeal cavity is called pharynx, which opens into oesophagus.
Oesophagus: It is broad, short muscular tube which opens into stomach.
Stomach: The stomach is large, thick walled muscular bag. Anterior part of stomach is called cardiac part and posterior part is called pyloric part. It is internally folded. It stores ingested food. Posterior part consists of pyloric constriction through which food is slowly passed.
Intestine: It is long, coiled part which starts from pyloric constriction. Intestine is divided into two parts.
Duodenum: it is c shaped structure, 3-5 cm long where hepatopancreatic duct opens.
Ileum: it is coiled part. It is about 20-25 cm long. Ileum is internally highly folded. Folding s is called villi, which increase absorptive surface.
Rectum: (large intestine): rectum is short, broad tube 4-5 cm long. It opens outside through cloaca and the opening id called cloacal aperture. The rectum stores undigested food for short time. Internally rectum is also folded.
Digestive glands
1. Gastric glands: They are present on the stomach wall. They secret HCL and enzyme pepsinogen.
2. Liver : It is large gland. It has two lobe-right lobe and left lobe. Liver is reddish brown in color. Left lobe is again divided into two lobes. There is a small sac like thin walled bladder present on right lobe called gall bladder. The duct of gall bladder is called cystic duct. The duct of liver is called hepatic duct. Liver secretes bile and excess bile is stored by gall bladder. Then both cystic and hepatic duct merge forming common bile duct. Common bile duct run through pancreas and receives pancreatic duct to form hepatopancreatic duct, which opens into duodenum.
Functions:
· The liver secrets bile, which is used in small intestine for digestion of food.
· It regulates the amount of sugar in the blood.
· It maintains the protein concentration in blood.
· It stores copper and iron and forms vitamin A.
· It kills many bacteria.
3. Pancreas : The pancreas is second largest gland. It is flat and irregular lobed gland. It has two functions
· It secrets hormones insulin which directly mix with blood.
· It secret pancreatic juice which contain several enzymes which is poured into duodenum through duct. The enzymes help digestion of ingested food.
· Therefore, pancreas acts as both endocrine and exocrine glands as it does secrets insulin and pancreatic juice respectively.
Functions:
· Enzymes secreted by pancreas helps in digestion of ingested food.
· Hormones secreted by pancreas helps in metabolism of carbohydrates and regulate the storage glycogen in liver and muscles.
4. Intestinal glands : Intestinal glands are found on wall if intestine. They secrete a kind of juice called intestinal juice, which contains several enzymes.
Physiology of digestion
· Frog is insectivorous (insects eating).
· The prey is captured by the action if tongue and swallowed without mastication.
· The food becomes lubricated by mucous secreted by mucin gland. (Salivary gland is absent). When the food reach to stomach the chemical digestion starts.
In stomach
· The gastric glands present on stomach wall secrete HCl and the Pepsinogen enzyme.
· The food is mixed with HCl. the HCl kills the bacteria, and softens the hard food.
· The pepsinogen is inactive enzyme. But in presence of HCl, it becomes active and then it is called Pepsin which digests protein into proteases and peptones.
· Pepsinogen----------------Pepsin
· Protein---------------------Proteoses and peptones
The food becomes creamy fluid called Chyme. From the pyloric constriction, the chyme slowly moves towards duodenum.
In Duodenum
The food is mixed with bile and pancreatic juice.
Bile: It is a kind of alkaline juice secreted by liver. It has mainly two functions like It neutralizes the acidic food and It emulsifies fat i. e. the fat droplets are broken into fine droplets and mixes with the food.
Pancreatic Juice: It is also a kind of juice secreted from the pancrease. It contains following enzymes
Trypsinogen - In presence of enterokinase it is converted into trypsin and the trypsin digests the protein into peptones and polypeptides.
Trypsinogen---------------------Trypsin
Protein----------------------------Peptones and polypeptides.
Amylase - It digests the carbohydrate into maltose.
In Ileum
The food is mixed with intestinal juice in ileum, which contains following enzymes.
Eryption: It digests peptones and proteoses into amino acids.
Peptidase: It digests peptides into amino acids
Sucrase: It digests sucrose into glucose.
Maltase: It digests maltose into glucose.
Lactase: It digests lactose into glucose.
Nucleotidase: It digests nucleic acid into nucleotides.
Absorption
The completely digested food material contains glucose, amino acids, fatty acids, glycerols etc. The simple molecules like water and minerals are not required to digest. All these simple compounds are now absorbed through the villi of intestine. There are two methods to absorb food materials. The food materials are absorbed by diffusion or osmosis through the villi and are mixed into the blood around the intestine. It is slow process and food molecules pass into blood from the high concentration in lumen of intestine. This method is called passive method. There is another method of absorption i.e. active method. It is fast and the food molecules are absorbed by using energy against concentration gradient from the lumen of intestine into the blood. The energy used in this method is ATP. Hence, all the food materials are absorbed completely into the blood. The remaining undigested and unabsorbed materials are stored in rectum for short time and ultimately passed out through the anus.
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Biology
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