Digestion

When foods are eaten they must be changed into smaller molecules of nutrients before they can be absorbed into the blood. Once broken down, the nutrients are carried around the body through the bloodstream and the body uses them to build and nourish cells; and to provide energy. Food travels though the digestive tract by muscle contraction called peristalsis. This journey of digestion can take up to twenty four hours.
Digestion begins in the mouth where the teeth break food down into smaller particles during mastication. Salivary glands secrete saliva which begins chemical digestion and keeps the food moist. Swallowed food is pushed into the pharynx by the contraction of multiple muscle of the face, neck and tongue. The soft palate blocks the upper pharnx to prevent the food from entering the nasal cavity. The epiglottis, a flap of cartilage, prevents the food going down into the respiratory tract. The food now called bowlus, travels down the oesophagus through and enters the stomach.
Folds in the stomach called rugae allow for expansion as the stomach fills. The stomach cells produce hydrochloric acid, pepsinogen and various regulatory hormones that chemically digest the bowlus. Muscular contractions in the stomach churn the contents and mix it with stomach secretions to form a thick liquid called chime.
The stomach is a muscular-walled sac that stores the bowlus. In addition , churns and mixes; with gastric juices produced in the stomach. The lower part of the stomach mixes this by muscle action. It then slowly empties the contents into the small intestine. Fats stay in the stomach the longest followed by protein and carbohydrate.
As food dissolves into juices from the pancreas, liver and intestine, the contents in intestine are mixed and pushed to allow further digestion. Finally nutrients are absorbed through the intestinal walls and transported through the body.
The waste product of this process unclude undigested food and fibre as well as older cells shed from the mucisa is pushed into the colon until faeces expelled by bowel and bowel movement.
Throuhgout this processes enzymes are produced by digestive glands. Enzymes speed up the chemical reaction whithin the body. The first acting gland is the salivary gland producing saliva. The saliva begins to digest the starch from food.
The next glands are found int the stomach lining. They produce stomach acid and enzmes that digest protein. The stomach itself if protected from the acid with a thick layer of mucosa lining it.
Once the food and juice mixture enters small intestine the pancreas and liver producesjuices which mix with the food. Pancreas juices contain enzymes that break down carbohydrates, fats and protein in food. Liver produces the bile, the bile acids dissolve fat into watery contents much loke detergents dissolve greace. After fat is dissolved it is digested by juices from pancreas and small intestine.
Most digested molecules, food water and minerals are then absorbed though the small intestine. The mucosa of the small intestinecontain many finger like projections called villi, which create a large surfacesurface allowing through which nutrient are absorbed. This is though special cells in =to the blood and carried away though stream to other parts of the body. This process varies depending on the type of nutrient.
Carbohydrates contain starch and fibre. The digestible carbohydrate is starch and sugar. Once broken down by saliva, juices from pancreas and the lining of the small intestine. First enzyme breaking starch into molecules is maltose – saliva and pancreatic juices. Then ezymes from small intestinesplits maltose into glucose that can be absorbed through blood. Glucose is carried through the stream to liver where it is strored and later used for energy.
Sugars are digested in small intestine were sucrose turns into glucose and fructose which absorb through the intestine. Milk contains lactose and changed into small molecules in small intestine. Fibre is indigestible and moves through digestive tract without being absorbed.
Proteins are larger molecules and enzymes in stomach start to the digestion process. In the small intestine several juices from the pancreas and the lining of the small intestine complete the breakdown of large molecules to smaller molecules called amino acids which can be absorbed and carried to other parts of the body.
Fats water content are initially dissolved into watery content in intestine. Bile acid from the in intestine produced in liver dissolve fat into tiny droplets allowing pancreatic and intestinal enzymes to break down molecules to allow absorption. Fatty acids and cholesterol are examples of these molecules. Bile acids combined with fatty acids and cholesterol help molecules move into cells of mucosa. These molecules which contain mostly pass into vessels called lymphallics near intestine, these vessels carry reformed fat to veins of the chest and bloodstream takes the fat to storage in various parts of the body.