The Digestive System of a Rat

Prelab Prepare the dissection tray and equipment. Put on your gloves. Retrieve your rat from the bins on the cart. They are sorted into first semester classes. Remove the skin from around your rat and place the skin back in the zip-lock bag.

Salivary Glands Lay the rat in the dissection pan ventral side upward. If the salivary glands were not injured during the skinning of the rat, find them now. If there is still skin on the neck, carefully remove the skin. Complete the “salivary gland” portion of the lab.

Oral Cavity It is extremely difficult to pry open the mouth of preserved specimens. Use a scissors to cut into the corners of the lips. Cut to the masseter muscle and then cut through the bone. Pry open the mouth. Pull down the lower jaw to expose the epiglottis. Find the incisors and molars.

Oral cavity continues Find the tongue, hard palate and soft palate. Complete the “oral cavity” section of the lab.

Dissection Using the photo as a guide, make cuts starting at the star and moving upward to the salivary glands. Continue with cut 2 and cut 3.

Dissection continued After the muscle layers have been cut you may find a fine membrane, the peritoneum, which lines the inside of the abdominal cavity. If necessary, cut through the peritoneum and expose the organs. Wash out the abdominal cavity if it is full of excess preservative fluid and coagulated blood.

Find the diaphragm. Note how it separates the thoracic cavity from the abdominal cavity.

Find the structures of the Thoracic cavity trachea

Thoracic Cavity continued Heart Diaphragm

Thoracic Cavity continued Lungs Diaphragm

Thoracic Cavity continued Note: Most people remove the heart and lungs in order to see the esophagus. Esophagus Complete the “Thoracic Cavity” portion of the lab.

Abdominal Cavity Below the diaphragm find the liver. Note that it is the same color as the lungs. Be careful not to get them mixed up on the test!

Abdominal Cavity continued Lift the liver to find the Stomach. You many also see the spleen and kidney which are not part of the digestive system.

Abdominal Cavity continued Next differentiate between the small intestine and large intestine. Note: The large intestine is often filled with feces.

Abdominal Cavity continued Cut the digestive tract at the distal end of the esophagus and the proximal end of the small intestine. This will allow you to remove the stomach. Open the stomach with your scissors by cutting along its longer, convex border, which is known as the greater curvature. Begin on the left side and continue along the posterior border. Empty the contents of the stomach on to a paper towel. Describe what you see.

Abdominal Cavity continued

Abdominal Cavity continued Wash out the stomach. Examine the pyloric sphincter at the distal end which regulates the release of partially digested food into the small intestine. Look along the inner walls of the stomach and note the rugae or folds. (If your stomach was completely full, the folds may be absent. Answer the “stomach” questions of the lab.

Abdominal Cavity continued The coils of the intestine are held in place by a fine peritoneal membrane, the mesentery. The mesentery will be visible as a fine, thin membrane. It is responsible for the coiling observed in the intestine. Note its shiny appearance.

Abdominal Cavity continued Remove the intestines from the rat. Cut through the mesentery until they are completely unraveled. Measure the length of the intestine and record the results. See the next slide for additional information regarding the intestines.

Abdominal Cavity continued The caecum is the beginning of the large intestine in the rat. Determine its functions and record your answer .

The waste product of digestion is feces!

1. Throw the organs removed from your rat in the garbage. 2. Spray your rat with preservative. 3. Put the skin back on the rat and spray it again. 4. Place the rat in your bag and keep it in your cabinet. 5. Finish the rest of the lab questions. They are due tomorrow.