IndexMouthEsophagusStomachSmall IntestineRectumMouthThe mouth chews food by using the teeth to tear, chew, and mince the food. The tongue has skeletal muscles (involuntary muscles) that move food around the mouth for efficient mechanical digestion. The salivary glands under and at the back of the tongue secrete saliva which allows for easier swallowing to begin chemical digestion. Saliva is composed of 95.5% water and the remaining 4.5% of a complex mixture of ions, glycoproteins, enzymes, growth factors and waste products. Say no to plagiarism. Get a tailor-made essay on "Why Violent Video Games Shouldn't Be Banned"? Get an original essay Saliva contains an enzyme called salivary amylase. This is a primary enzyme in saliva. Amylase begins to break down starches in foods. Starches are long chains of sugars stuck together, amylase breaks the bonds along the chain to release maltose sugar molecules. At a lower temperature, salivary enzymes are deactivated and at a higher temperature, the enzyme is denatured. Therefore, it takes an enzyme longer to digest starch at a lower or higher temperature. The optimal pH for salivary amylase enzymatic activity ranges from pH 6 to pH 7. If higher or lower than this range, the reaction rate is reduced as the enzymes are denatured. At pH 6.8 the salivary amylase enzyme is more active. The stomach has a high level of acidity which causes salivary amylase to denature and change its shape. Salivary amylase does not work once it enters the stomach. The esophagus connects the pharynx to the stomach. Involuntary contractions called peristalsis (two layers of smooth muscle, the outer longitudinal and the inner circular) push food through a ring of soft muscles that close the opening in the body called the sphincter to the lower esophageal sphincter. All sphincters located in the digestive tract help to move along the digested material in one direction. Esophagus Once food has passed through the chemical and mechanical process of the mouth, the pharynx transports the food to the esophagus and larynx. When food is swallowed, the epiglottis closes over the trachea to prevent food from entering the trachea and causing suffocation. Stomach The stomach is a hollow, rounded organ located just below the diaphragm on the left side of the abdominal cavity. Located between the esophagus and duodenum, it is a rough, crescent-shaped enlargement of the gastrointestinal tract. The inner layer has wrinkles known as gastric folds. The gastric folds allow the stomach to stretch, accommodate large amounts of food, and help grip and move food during digestion. When food reaches the stomach, it undergoes chemical and mechanical digestion. This is when peristaltic contractions (mechanical digestion) begin to blend the food. This mixes with the strong gastric digestive juices that the cells of the stomach lining secrete (chemical digestion). There are three layers of smooth muscle lining the stomach wall, arranged in longitudinal, circular, and oblique rows. Muscles allow the stomach to churn and squeeze food during mechanical digestion. When food is mixed with gastric juices to produce chyme, enzymes in the gastric juice chemically digest the large molecules into smaller subunits. Gastric lipase splits fatty triglycerides into fatty acids and diglycerides. Pepsin breaks down proteins into smaller amino acids. Chemical digestion begun in the stomach will not be complete until the chyme reaches the intestine, but it prepares hard-to-digest proteins and fats forfurther digestion. The stomach initiates the chemical digestion of proteins. The stomach enzyme pepsin begins to break down most of the proteins found in the food secretion of the stomach lining which consists of approximately two liters of hydrochloric acid (HCI), pepsin and other fluids that make up the gastric digestive fluids each day. This fluid is extremely acidic, which helps kill any bacteria and other pathogens that may have been digested. The stomach lining produces thick mucus to prevent it from being damaged by acid. Failure to produce enough mucus or producing too much acid can lead to the formation of peptic ulcers. The food stays in the stomach for about 3-4 hours, then moves through another sphincter muscle that passes into the small intestine. Small IntestineAfter passing through the stomach and entering the small intestine where the nutrient liquid and small solid residues are exposed to more chemical digestion via enzymes from the pancreas and bile from the liver as peristalsis. The small intestine is nearly 7 meters long and is folded and curled into a small area of ​​the abdominal cavity. The surface of the small intestine is covered with projections called villi. A single villus consists of a vein, an artery and a central milk, this is a type of capillary that carries lymphatic fluid. The villus is supported by a strand of muscle and connective tissue. There are two types of cells lining the villi, goblet cells, which secrete mucus, and epithelial cells responsible for absorption. The epithelial cells are lined with even smaller projections called microvilli, which further increase the absorptive capacity in the small intestine. Microvilli are lined with digestive enzymes, which break down carbohydrates and proteins. When food sits in the stomach it is broken down and forms a substance called chyme, this is a thick semi-fluid mass of partially digested food and digestive secretions that forms in the stomach and intestines during digestion. When it passes through the small intestine it encounters the villi. Carbohydrates and proteins present in chyme enter the bloodstream through veins and arteries. The fat is then absorbed from the milk into the lymphatic system and finally flows into the bloodstream. The process called active transport specializes the intestinal villous cells allowing the passage of B-12, calcium and iron into the bloodstream. There are three distinct parts to the small intestine, the duodenum, the jejunum, and the ileum. Every day approximately nine liters of fluid enters the duodenum. Most chemical digestion occurs in the duodenum using chemicals secreted by the liver, pancreas, and small intestine. The other two sections are the jejunum and ileum, they absorb food molecules through the directional villi into the bloodstream. It is at this point that the body finally receives nutrients from food through the bloodstream. The process is highly dependent on activity across a vast network of nerves, hormones, and muscles. Carbohydrate digestion begins in the mouth with enzymes found in saliva, then continues in the duodenum with the enzyme amylase, which secretes into the duodenum from the pancreas. Intestinal cells use the enzymes sucrase, maltase and lactase. Fat breaks down with the help of lipase enzymes, which secrete from the pancreas. The trypsin enzyme of the pancreas and the intestinal peptidase enzymes continue the process. Carbohydrates and fats finish digestion in the second section of the small intestine, while most carbohydrate and fat absorption occurs in the duodenum and jejunum. The main purpose of fasting is to absorb nutrients; therefore, it has the structure of villi and microvilli. It also absorbs most proteins. The function.