THE DIGESTIVE SYSTEM OF THE FROG The digestive organs are usually divided into two main groups. The gastrointestinal tract or the alimentary tract and The accesory organs. The gastrointestinal tract (alimentary tract) -is a continuous tube running from the mouth to anus. This compose of mouth, parynx, esophagus, stomach, small intestine and large intestine. The accesory organs -is a group of organs consist of organs such as the teeth, tongue, liver, gallbladder and pancreas. *Place the preserved frog in a dissecting pan. open its mouth and study the roof and the floor of the mouth. may be necessary to cut through the Joint between the upper and lower Jaw in order to expose the buccal cavity. *Identify the stuctures below: Maxillary teeth – these are rows of small teeth along margin of the upper Jaw. Sulcus marginalis – this is a pair of groove on the inner side of the maxillary teeth that receives the lower Jaw when the mouth is closed. Median subrostral fossa – it is a prominent depression of the sulcus marginalis at the anterior tip of the upper Jaw. Lateral subrostal fossa – it is a pair of depression of the sulcus marginalis lateral to he pulvinars.
Pulvinar rostrale – it is a pair of low elevations on each side of the median subrostal fossa. Internal / posterior nares or choanae – it is a pair of slit-like openings above the eyeballs leading to the external nares. Eyeball (orbital) prominence – these are two large rounded bulges of the eyeball. Vomerine teeth – these are fine teeth projecting from the vomers in between the internal nares. Opening of Eustachian tube – it is a pair of slit-like openings found medial to the angles of the Jaw. the eustachian tube leads to the cavity of the middle ear.
Prelingual fossa – these are two shallow depression on each side of tuberculum prelinguale. Tuberculum prelinguale – it is a prominent median elevation at the tip of the lower Jaw. this fits into the median subrostal fossa when the mouth is closed. Tongue – it is a forked muscular organ attached to the anterior tip of the lower Jaw. Opening of vocal sac – this is a pair of slit-like opening on the floor of the mouth close to the angle of the Jaw; found only on male frogs. Opening of esophagus – it is a large transverse slit, posterior to the laryngeal prominence.
Laryngeal prominence – ircular elevation anterior to the esophageal opening. Glottis – it is a short vertical like opening at the center of the laryngeal prominence. *Position the frog on the dissecting pan with the ventral side up. *Pin the limbs to the dissecting pan . with the use of a forcep, grasp the posterior end of the rectus abdominis and cut anteriorly the ventral wall. the cut made should be along the sides of the linea alba so as not to cut the anterior abdominal vein, which is directly underneath the linea alba. Lift the muscles carefully before cutting so as not to cut the underlying organs. hen cut transversely the rectus abdominis at the level af the abdominal wall near the bases of the thigh. *Identify the rest of the internal organs of the digestive system. Pharynx – it is the posterior portion of the buccal cavity which opens into the esophagus. Esophagus – it is a very short tube that connects the pharynx to the stomach. Stomach – a large whitish organ with either “U” or “J” shaped enlarged portion of the Digestive tube. ts anterior or cardiac end is smaller than its posterior or pyloric end; it curves more on the outer side (the lesser curvature); this rgan is suspended from the dorsal body wall by a mesentery known as the mesogaster. Pylorus – this is a constriction at the posterior end of the stomach. Spleen – this is a dark reed organ located on the left lateral side of the stomach. it is considered part of the lymphatic system and functions in phagocytosis, production of lymphocytes and blood storage. Gallbladder – this is a small greenish sac located at the ventral part of the median lobe of liver. his stores bile secreted by the liver. Small intestine – this is a slender and longest portion of the tube which is irregularly oiled;anterior portion is the duodenum which is wider but shorter and the more posterior, narrower and longer coiled division of the small intestine is the ileum; the small intestine is suspended from the dorsal body wall by the mesenterium. Large intestine – this is a short dilated tube at the terminal end of ileum. it is suspended by the mesorectum, where a rounded reddish spleen is also suspended.
Cloaca – this is the posterior dilated end of the large intestine located within the pelvic girdle. different eurogenital organs (i. e. urinary bladder, mesonephric ducts and ovisac) also pen to this area. Anus – it is a small opening at the posterior end of the cloaca. DIGESTIVE GLANDS Liver – this is a large reddish brown organ on the anterior portion of the pleuro- peritoneal cavity; this large organ that partly covers the stomach; this is divided into left, median and right lobes which are suspended from the body wall by a ventral ligament. at its ventral side of the median lobe is the gallbladder. he bile which is secreted by the liver and stored by into the gallbladder by way of two fused ducts, the hepatic ducts coming from the left and right lobes of the liver. A cystic duct is a tiny duct connected to the neck of the gallbladder; the large duct formed by the cystic hepatic and pancreatic duct is the common bile duct-this is surrounded by the tissues of the pancreas and this duct enters the doudenum, emptying its content on this part of the digestive tube. Pancreas – this is a small elongated and irregularly shaped gland located between the stomach and duodenum;ba pancreatic Juice to the duodenum.
THE HUMAN DIGESTIVE SYSTEM What is digestion? -digestion is the process of pondering food using our digestive system. digestion takes place within a tube called digestive canal which starts with the mouth and ends with the anus. digestion reduces food into small soluble molecules that can be absorbed by the lining of the digestive canal. the cooperative effor of the different parts of the body is essential for the digestion food. The digestive process: 1 . ) Food received in the mouth is chewed by the teeth and softened by a digestive enzyme in the saliva. 2. ) The chewed food is conveyed by the tongue into the pharynx thorastic cavity. he peristaltic movements of the esophagus walls pushes the food own into the stomach. 4. ) The bolus of food is churned and mixed in the stomach where digestive Juices and enzymes act on them. normally, the stomach empties in two to six hours. by this time the bolus food has become semiliquid food mass called acid chyme. 5. ) Acid chymes leaves in the stomach and enters the small intestine in small squirts only, ensuring a slow thorough rate of digestion. the first 25 cm, of the small intestine is called the duodenum. two glands, the liver and the pancreas, sends secretions to the duodenum. he liver makes bile which is stored in the gallbladder nd sent by way of the bile duct to the duodenum. the bile salts emulsifies fats and breaks them into fat droplets for easy absorption. the pancreas send pancreatic Juice into the duodenum by way of the pancreatic duct. The pancreatic enzymes, amilase trypsin, and lipase digest starch, protien and fat droplets, respectively. the digestive enzymes in the walls of the small intestine completes the digestive process. 6. ) Food that cannot be digested in the small intestine passes on into the large intestine down to the rectum and out through the anus as faeces.
