ANIMAL NUTRITION
Digestion
1. It is process of simplification of insoluble complex foodmaterials into soluble simple food materials, for easy absorbtion. It involves physical (mechanical) and chemical breakdown of various food materials . During the process carbohydrate is converted into glucose, proteins are converted into amino acids and lipids are converted into fatty acid and glycerol.
Types of digestion
Digestion is classified into two types, based on the site where digestion of occurs. They are
1. Intracellular digestion - When digestion takesplace inside the cells, it is called intracellular digestion. In this type, the cell engulfs food materials by endocytosis. Then they are digested by the enzymes inside the cells and the digested products diffuse into the cytoplasm.
Eg:- Protozoans and sponges
2. Extra cellular digestion:- When digestion takesplace outside the cells, It is called extracellular digestion. All the animals provided with alimentary canal exhibit extracellular digestion. Here digestion occurs inside the lumen of alimentary canal.
Digestive system:- It consists of alimentary canal and digestive glands.
Alimentary canal:- It includes mouth, buccal cavity, pharynx, oesophagus, stomach, small intestine, large intestine, rectum and anus.
Mouth is surrounded by lips. It leads into buccal cavity which contain teeth and tongue. The tongue is essential for ingestion, mastication, deglutition, taste and speech.
The teeth are thecodont- placed in sockets and heterodont - there are four types of teeth present, (i) cheisel shaped incisors used for cutting the food materials (ii) dagger shaped canines employed for tearing or piercing the food materials, (iii) premolars and (iv) molars. The last two types are used for grinding the foodmaterials. Therefore known as grinders.
The bucculcavity receives the duct of three pairs of salivary glands -- parotid , submaxilary and sublingual glands - produce saliva, which contain a starch digesting enzyme ptyalin (salivary amylase)
The buccul cavity leads into pharynx, the common chamber for digestive and respiratory systems. It leads into oesophagus, which distally opens into stomach.
The stomach is J shaped and consists of cardiac, fundic and pyloric parts. Fundus is the main stomach. Pyloric stomach is also known as antrum. The stomach is provided with the large number of gastric glands which produce gastric juice. The gastric gland consists of oxyntic cells (parietal cells) - produce hydrochloric acid, chiefcells or zymogen cells or peptic cells - produce pepsin and rennin and mucous cells - produce mucous. The pyloric stomach opens into the small intestine by pyloric orifice, gaurded by pyloric sphincter.
The small intestine has three regions . U shaped first part is known as duodenum, receives a common bile duct from pancreas and liver. The jejunum followes duodenum and is longer and more coiled. The last part- ileum is also highly coiled and opens into the large intestine. The small intestine is provided with large number of intestinal glands (crypts of Liberkuhn) produce intestinal juice or succuss entericus.
At the junction of small intestine and large intestine there is a finger like structure called vermiform appendix. It is vestigeal in man but involved in immune mechanism by producing lymphocytes and antibodies.
The large intestine consists of colon and rectum. Human colon consists of an ascending colon, a transverse colon, a descending colon and a pelvic colon. The pelviccolon continues into the rectum which opens to the exterior through the anus. The large intestine secretes no enzymes but serves to store unabsorbed food materials temporarly It also helps for the absorbtion of water.