Digestive System In Ruminents And Rodents 27pf

Digestive System in Ruminents and Rodents Herbivores like ruminants and rodents feed on plants which contain a high percentage of cellulose, a polysaccharide which is extremely insoluble. They obtain most of their energy from the breakdown of cellulose of plant cell walls. The enzyme cellulose is required to break down cellulose but is not produced by these animals. They solve this problem by having digestive systems which are specially adapted to carry out cellulose digestion. Ruminants like cows and goats have stomachs which are divided into four chambers, namely rumen, reticulum, omasum and abomasums. This adaptation enables ruminants to carry out rumination, the process of regurgitating and rechewing food. The firsts two chambers, the rumen and reticulum, are specialised compartments which harbour large communities of bacteria and protozoa. These microorganisms are able to produce cellulose that digests cellulose. 1. Partially chewed food is ed to the rumen, the largest compartment of the stomach. Here, cellulose is broken down by the cellulose produced by bacteria. Part of the breakdown products are absorbed by the bacteria, the rest by the host. 2. As the food enters the reticulum, the cellulose undergoes further hydrolysis. The content of the reticulum, called the cud, is then regurgitated bit by bit into the mouth to be thoroughly chewed. This process helps soften and break down cellulose, making it more accessible to further microbial action. 3. The cud is reswallowed and moved to the omasum. Here, large particles of food are broken down into smaller pieces by peristalsis. Water is removed from the cud. 4. The food particles finally move into the abomasum, the true stomach of the cow. Here, gastric juice containing digestive enzymes completes the digestion of proteins and other food substances. The food then es through the small intestine to be digested and absorbed in the normal way. In rodents like rabbits and rats, the caecum and appendix are enlarged to store the cellulose-digesting bacteria. Unlike ruminants, the breakdown products through the alimentary canal of rodents twice. The faeces in the first batch are usually produced at night. These are then eaten again to enable the animals to absorb the products of bacterial breakdown as they through the alimentary canal for the second time. The second batch of faeces becomes drier and harder. This adaptation allows rodents to recover the nutrients initially lost with the faeces. Absorption and Assimilation of Digested Food To enter the body cells, nutrients in the lumen of the small intestine must be transported across the intestinal lining into the bloodstream. Ileum, the last part of the small intestine, is the major site of nutrient absorption.

The wall of the small intestine is covered with epithelial cells that are specialised to complete digestion and absorb the resulting nutrient molecules. The small intestine, with a length of about 6m, is the longest section of the alimentary canal. The intestinal lining is highly folded and covered entirely by tiny, finger-like projections called villi. The epithelial cells of a villus have a lining of microscopic projections called microvilli, each about 1µm long. These collectively form the brush border which further increases the surface area available for absorption. The epithelial lining is only one cell thick. Each villus also has a network of blood capillaries and a lymphatic vessel called a lacteal. Overall, this structural adaptation greatly increases the rate of nutrient absorption through the intestinal wall. Absorption of digested food Nutrient absorption involves both diffusion and active transport. Initially, glucose, amino acids, water-soluble vitamins and minerals diffuse into the epithelial cells and are absorbed into the capillaries. Subsequently, the transport of the remaining nutrients across the epithelial lining involves active transport during which energy is used. In contrast, glycerol and fatty acids enter the epithelial cells, where they recombine to form tiny droplets of lipids, which then move into the lacteals. Fatsoluble vitamins are also absorbed into the lacteals to be transported together with lipids. The lacteals converge into larger vessels of the lymphatic system. The fluid carrying lipids and fat-soluble vitamins enters the lymphatic system which forms a network throughout the body. The contents are then drained into the right lymphatic duct and thoracic duct before being emptied into the bloodstream through the subclavian veins. Capillaries that drain water-soluble nutrients away from the villi converge into the hepatic portal vein, which leads to the liver. From here, the nutrients are transported to all cells in the body. About 7 to 8 litres of water from drinks and from various digestive juices enter the alimentary canal every day. Together with the small intestine, the colon reabsorbs almost 90% of the water and minerals. In the colon, water and minerals are reabsorbed into the cells lining the colon, and subsequently into the bloodstream, so that we do not constantly lose them.