Materials / Reagents Required :

            10 % Neutral Buffered Formalin (NBF), Normal saline (10 litre), 70 % Ethanol (1 litre), different sizes of scissors, forceps, scalpel, spatula, bone cutter, cardboard paper, etc.

Safety Precautions :

            Protective equipments including laboratory coats, gloves, apron, etc., should be worn during euthanasia, necropsy as well as during the preparation of the solutions.

Procedure :

• Stomach appears as a sac-like structure and consists of forestomach and glandular stomach, the forestomach being 60 % of the total volume in distended condition. The forestomach mucosa is white and glistening and is well demarcated from the glandular stomach by the limiting ridge. The glandular stomach is red to grey red in colour. The folds present on the walls (mucosal surface) of stomach are called as rugae. The stomach opens to the duodenum through the pyloric sphincter. 
• Small intestine consists of  the duodenum (anterior portion that connects stomach with the rest of small intestine), the jejunum (the second portion) and the  ileum (posterior portion that connects with the caecum of large intestine),which can be differentiated histologically.
• Large intestine consists of a large caecum (that appears as a blind sac), colon and rectum. The caecum is quite large in rat and contains microorganisms which  breakdown the plant material not already digested by the enzymes of the small intestine. 
• Peyer's patches (Mucosa associated lymphoid tissue) are observed as grey to white elevated nodules on the anti-mesenteric border of the intestine, especially at the distal ileum. 
• Liver occupies the anterior third of the abdominal cavity extending from the vertebrae to the xiphoid cartilage. In rats, it consists of four lobes; left lateral lobe, median (incompletely separated into right and left sub-lobes), right lateral lobe and caudate lobe. Blood is supplied to the liver by i) the portal vein (which drains the gastrointestinal tract providing 60-70% of the afferent hepatic blood flow) and ii) the hepatic artery (which provides oxygenated blood from the aorta). The hepatic vein drains the blood from the liver into the caudal vena cava.
• Pancreas appears as a diffuse gland embedded in the mesentery proper and greater omentum adjacent to the stomach and spleen. It is found along the anterior edge of the duodenum, immediately after the stomach. Pancreas appears gray-white to pinkish tan in colour. Pancreas consists of the head, body and the tail. The head is found in the mesentery of the duodenal loop, the body in the greater omentum of the stomach and the tail extends into the gastrosplenic ligament adjacent to spleen. Pancreatic  excretory ducts join to form the main ducts which join to form the common bile duct which empties into the duodenum. 

Collection of stomach, intestine, liver and pancreas :

• After induction of anaesthesia/euthanasia, the fur of the animal shall be moistened with alcohol to prevent the fur from getting adhered into the tissue samples.
• Normal saline shall be kept ready during the necropsy to keep the lungs moist.
• Skin of the abdomen (in the shape of V) along with mammary gland shall be removed first.
• The abdominal cavity shall be opened with a V shaped cut at the abdominal muscles.
• The gastro-intestinal (GI) tract consisting of the stomach, small and large intestine is removed as a whole along with mesenteric lymph nodes.
• The liver shall be removed first by cut.
• The stomach shall be opened along the greater curvature for observing its mucosa after washing out its contents.
• Observe the presence of the folds (rugae) on the mucosal surface.
• Separate the small intestine. Open and wash it clean and examine the mucosal surface for its velvety texture.