Objective :

• To learn the procedure for collection of different parts of digestive system
• To learn the structure of the digestive system of rat

Theory :

• The digestive system is composed of the mouth, esophagus, stomach, small intestine, large intestine, rectum and anus and associated glands liver and pancreas.  The digestive system obtains and processes food for the all of the cells in an organism. The stomach stores and macerates the food and begins the early phase of digestion.
• The small intestine of the GI tract is primarily responsible for digestion, secretion and absorption of nutrients. Digestive enzymes from the pancreas and the intestine itself are secreted into the lumen of the small intestine where the chemical breakdown of food occurs. It also acts as a barrier to the passage of luminal contents into the body and serves as a channel for the undigested ingesta to pass out of the body.
• In the proximal small intestine, passive movement of sodium and water is from the blood to the GI tract lumen and vice versa in distal small intestine. The large intestine stores the digesta for further breakdown or excretion, absorption of specific nutrients and absorption / secretion of water and electrolytes. The caecum is primarily involved in microbial fermentation and storage of ingesta.
• The bacteria present here facilitate in detoxifying or bioactivating ingested compounds and producing essential vitamins. Re-absorption of the large quantities of water occurs in the large intestine resulting in a mass of waste material, thefaeces. Faeces are stored in the rectum until eliminated through the anus. 
• The gall bladder that stores the bile  is absent in the rat. The bile produced in the liver passes directly to the duodenum, via the bile ducts. Liver is involved in metabolism of nutrients, detoxification of metabolic wastes, synthesis of bile, plasma proteins / lipoproteins, etc. The pancreas secretes digestive enzymes as well as hormones (insulin and glucagons).