The digestive system is made up of the digestive track which consists of a series of hollow organs which are joined in a long and twisting tube from the mouth to the anus, together with other organs which also help in the break down and absorption of food in the body. The following diagram illustrates and describes the digestive system.The organs that make up the digestive system are the mouth, esophagus, stomach, small intestine, large intestines also known as the colon, rectum and the anus. A lining called mucosa covers the inside of these hollow organs. There are tiny glands in the mouth, stomach, and the small intestine which produce the juices that help in the digestion of food. The breakdown and the movement of food in the digestive track are made possible by the presence of a layer of smooth muscles (NDDIC, 2010).The liver and the pancreas are the two digestive organs that produce juices that reach the intestine through small tubes called ducts. The liver's digestive juices are stored in the gallbladder until they are needed in the intestines. Parts of the circulatory and nervous systems play a significant role in the digestive system (Smith and Morton, 2001).Importance of digestionDigestion is that process that breaks down food into small part that can be assimilated in the body to provide energy and nourish the cells, therefore when food such as meat, vegetables, and bread are taken in, they are in a form that cannot nourish the body, therefore the body has to change the food into smaller molecules of the nutrients that can be absorbed in the blood and transported throughout to the body cells (Johnston, 2004).Digestion of foodDigestion is the process that involves the mixing of food with the digestive juices, movement of food in the digestive track, and the breakdown of large food molecules into smaller ones. Digestion starts in the mouth, during the process of chewing and swallowing, and is culminated in the small intestines. The movement of food through the digestive track is made possible by the presence of a layer of muscles that makes the wall to move. The organ wall movement propels food and liquids through the digestive system mixing the food contents within each digestive organ. Peristalsis is the name given to the muscle action that makes food to move from one organ to another. Peristalsis is likened to a traveling ocean wave through the muscle. The contraction of the organ muscle creates a narrowing which then propels the narrowed portion down the length of the organ slowly. The narrowing waves push the food and the fluids through each of the hollow organ (Johnston, 2004).Swallowing food or fluids happen to be the first major movement of muscle that occurs. Once the swallowing process starts, it turns out to be an involuntary action and goes on through the action of nerve control. The swallowed food or fluid passes through the esophagus, which is a connector of the throat and the stomach. The junction between the esophagus and the stomach has a ringlike muscle, which is known as the lower esophageal sphincter, which closes the passage that exists between the stomach and the esophagus. The sphincter relaxes to allow the approaching food to pass to the stomach (Smith and Morton, 2001). The three mechanical tasks of the stomach is to, first, store the swallowed food and liquids. The stomach does this through the relaxation of the stomach on the upper part to allow in the large amounts of food and liquids. Second task is to mix digestive juices produced by the stomach with the swallowed food and fluids. The stomach's lower part does the mixing through muscle action. Third task is to drain its contents into the small intestines slowly.
There are several factors that do affect the emptying of the stomach; this includes the type of food and the emptying stomach and the small intestine degree of the muscle action. For example, carbohydrates spend the least time in the stomach followed by the proteins while the fats take the longest time (Johnston, 2004).After the food dissolves into the juices produced by the liver, pancreases, and intestine, the intestine contents are pushed onward for further digestion. Finally, the digested food nutrients get through the walls of the intestines and transported all over the body. Older cells shed from mucosa, and fiber undigested food parts, are the waste products of the digestion process. These wastes are pushed into the colon, where they are retained until the bowel movement expels the feces.The salivary glands are the first to act on food in the mouth. The saliva produced has an enzyme that acts on starch from the food. The enzyme digests the food into small molecules. A substance that speeds up chemical reaction in the body is known as an enzyme (Johnston, 2004).The stomach lining contains the next set of the digestive glands. The lining produces an enzyme that digests protein and stomach acid. The tissues of the stomach are protected from being dissolved by the digestive juices by the presence of the mucus layer which covers the mucosa.After the food and juice mixture are emptied into the small intestine, the food mixes with the other juices from the other digestive organs. The pancreases juice contains an extensive range of enzymes that digest the carbohydrates, fat, and protein. The intestinal walls also contain glands which produce enzymes that are active during the digestion process. Bile is produced by the liver and is stored in the gallbladder. During mealtimes the bile is squeezed out of the gallbladder, into the bile ducts, to the intestines where it is mixed with the fats in the food. Bile acid dissolves the fats in the food into the watery contents found in the intestines. The dissolved fats are the digested by the enzymes produced by the pancreases and the intestine lining (Smith and Morton, 2001).Absorption and transport of nutrients
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Absorption takes place in the small intestines where the digested food molecules, minerals and water are absorbed. The lining of the small intestine i.e. mucosa has many folds which are covered with villi, this are tiny fingerlike projections. Which are in turn covered by microscopic projections called microvilli. A large surface are for nutrients absorption is created by these structures. Some specialized cells also give way to the absorbed materials to cross the lining on the small intestines to the blood, where they are transported in the blood stream the other body parts for storage or advanced chemical change. The transportation process varies with the type of nutrients in question (Johnston, 2004).Carbohydrates; the body requires this type of food for the provision of energy. The following foods are rich in carbohydrates; potatoes, bread, beans, fruits, dried peas and vegetables. Starch and sugar are the digestible carbohydrates. They are broken down by the enzyme action in the saliva, pancreases juice, and small intestine lining into simpler molecules. The digestion of starch takes place in two steps. First the starch is broken down into maltose by the enzymes ion the saliva and the pancreases juice. Then maltose is broken down into glucose by the enzymes in the small intestine lining. Glucose is then carried in the blood stream to the liver for storage or is broken down to give energy for the work of the body (Smith and Morton, 2001).The digestion of sugar happens in one step. Sucrose also referred to as the table sugar, is digested to glucose and fructose by an enzyme found on the lining of the small intestine. Glucose and fructose are absorbed through the intestine wall into the blood. Lactose is another type of sugar found in the milk; it is changed by another enzyme in the intestinal lining into absorbable molecules (Johnston, 2004).Since fiber is indigestible, it passes through the digestive track without being acted upon by the enzymes. A variety of food contains soluble and insoluble fiber. The soluble fiber easily dissolves in water and assumes on a soft, gel-like touch in the intestines. On the other hand, insoluble fiber remains unchanged as they pass through the intestines (NDDIC, 2010).Proteins; foods that are rich in proteins includes beans, eggs, and meat. These foods contain large molecules of proteins which have to be digested by the enzymes before they can be used to repair and build the body tissues. Digestion of proteins starts in the stomach, whereby an enzyme in the stomach juice digests the swallowed protein. The complete breakdown of the large protein molecules is achieved through the action of several enzymes in the pancreases juice and the intestinal lining on the large molecules to small molecules known as the amino acids. Amino acids are easily dissolved in the blood stream, making it possible for them to be transported to all other parts of the body to build the wall and other parts of the cell (Johnston, 2004).Fats; the body gets most of its energy from the fats. Dissolving fats into the intestine watery contents is the first step in the process of fat digestion. The liver produces bile juice which dissolves the fat in small droplets thus giving the intestinal and the pancreases enzymes a fair chance to breakdown the large fat molecules into tiny ones. The small molecules consist of; cholesterol and the fatty acids. The fatty acids and the cholesterol combine with the bile and together they move into the cell mucosa. In the cell the tiny molecules are reformed again into large ones, most of which are able to pass into lymphatic vessels placed near the intestines. These vessels carry the reformed fats into the veins of the chest, whereby the blood transports the fats into the storage deports of the body (NDDIC, 2010).Vitamins; vitamins are vital parts of the food required by the body. The digestion of the vitamins occurs in the intestines. Vitamins are classified by the type of the different fluids that can dissolve them: fat soluble vitamins which includes (vitamins A, D, and K) and the water soluble vitamins which includes; all the B and C vitamins. The liver stores the fat soluble vitamins, whereas the excess water soluble vitamins are passed out as urine since they are not easily stored (Smith and Morton, 2001).Salt and water; water in which salt is dissolved, is the material which is mostly absorbed in the small intestines. The foods and the fluids we take and the digestive glands secreted juices are the main sources of the salt and water (Smith and Morton, 2001).Hormone controlled digestive processThe digestive process is controlled by the hormones which are produced by the cells in the mucosa lining of the small intestines and the stomach. Into the blood of the digestive track these particular hormones are released, they pass through the heart and though the arteries and they travel back to the digestive system stimulating the digestive juices and causing the movement of organs. The main hormones which are responsible in controlling the digestive process are secretin, gastrin, and cholecytokinin (NDDIC, 2010).Nerve controlled digestive processThere are two types of nerves that assist in controlling the digestive process.The first one is from outside also known as extrinsic whereby by the nerves entering the digestive organs come from the spinal cord or the brain. The nerves release two chemicals, adrenaline and acetylcholine. Adrenaline makes the stomach muscles to relax while the acetylcholine causes the muscles to contract (Johnston, 2004).The other one is from within known as intrinsic, this is a dense network of nerves in the walls of the stomach, small intestine, esophagus, and the colon. These intrinsic nerves get to action when the hollow organs walls are stretched by food thus releasing different substances which may delay or speedup the food movement and juice production by the digestive organs (NDDIC, 2010).As we have seen, digestion is a very important process in our bodies. The food we take cannot be of grate help if it is not digested. Digestion breaks down large molecules of food to tiny molecules which can be assimilated into the blood for transportation to other parts of the body. We owe the whole process to the digestive system. Since we take different kinds of food which require different kind of attention during digestion, the digestive system offers a strategic layout of events hence making it possible for the body to acquire relevant nutrients with reference to the food taken in.Therefore, together, the blood, hormones, nerves, and the digestive system organs carry out the multifaceted task of digesting and absorbing the required nutrients from the foods and the fluids consumed each and everyday. It should be noted that it is important to take care of the digestive system as it will help in the prevention of many diseases and as a result make a major contribution to the health well being of an individual.
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