Ingestion and food breakdown.docx

**Ingestion & Food Breakdown** ***F**OOD INGESTION AND BREAKDOWN, SWALLOWING, & PERISTALSIS* Food breakdown begins by chewing. Chewing is a way of breaking food down into smaller particles. Simply by chewing food begins the process of mechanical digestion. As a person begins to chew food, the food...

**Ingestion & Food Breakdown** ***F**OOD INGESTION AND BREAKDOWN, SWALLOWING, & PERISTALSIS* Food breakdown begins by chewing. Chewing is a way of breaking food down into smaller particles. Simply by chewing food begins the process of mechanical digestion. As a person begins to chew food, the food tastes sweet. This is the breakdown of a starch to a maltose. As a person chews, food mixes with saliva and an enzyme is secreted. The enzyme is called salivary amylase and it begins the process of chemical digestion for carbohydrates or more specifically for starches. Deglutition is another name for swallowing. It includes 2 phases **esophageal** and the pharyngeal phase. Eventually, food moves along the gastrointestinal tract and onward into the esophagus. This movement occurs by peristalsis, or contractions of the muscle walls. Eventually it will reach the lower Cardioesophageal sphincter located at the entrance to the stomach. *FOOD BREAKDOWN, THE ACTIVITIES OF THE STOMACH* Virtually no absorption occurs through the stomach walls. Instead, a number of processes occur, and these processes are important for the breakdown of the macronutrient proteins. It begins with gastric juices being secreted, and this process may be stimulated by the sight, smell, and taste of food. The function of gastric juices is to stimulate stomach cells to release gastrin. Gastrin is responsible for the production and activation of the enzyme pepsin, mucous, and hydrochloric acid. The high acidic environment is important because it activates pepsinogens to become pepsinogen. Another protein-digesting enzyme called rennin found to be produced in infants is responsible for the breakdown of milk/milk products. Finally, food is churned and mixed by the contraction of the stomach muscles. It now resembles a semi-liquid called chyme and is forced towards the pyloric sphincter. Eventually, small amounts of this fluid are moved into the duodenum. *ACTIVITIES OF THE SMALL INTESTINE* By the time food reaches the small intestine, both proteins and starches are partially digested. At this stage, the digestion of carbohydrates has not begun. However the chemical processes are beginning. There are a variety of enzymes that are very in the small intestine. These include: Brush border Enzymes which not only complete protein digestion also break down sugars to their mono/simple state. Pancreatic juice contains many enzymes which are responsible for the digestion of lipids, It is also responsible for partially digesting proteins. It also contains enzymes, lipases, that totally break down fats. Still on the subject of pancreatic, its alkaline pH of pancreatic juice changes the acidic chyme, ensuring the right environment for many enzymes found in the small intestine. These processes are quite complex, however by the time reaches the end of the small intestine, digestion is complete. As chyme enters the small intestine, it stimulates the production of two hormones, these are called secretin and CCK (Cholecystokinin). Both of these hormones are involved in the release of pancreatic juice from the pancreas. One of these hormones, CCK, entices the gallbladder to contract and as it does so it releases stored bile into the bile duct. If this process is impaired, the absorption of fats does not occur. *ACTIVITIES OF THE LARGE INTESTINE* No digestive enzymes enter the large intestine. Instead, vitamin K and B group vitamins are manufactured in the large intestine by bacteria. The process is aided by the absorption of water. Of the great quantity of water that is produced, only a small amount is excreted from the body in the faeces. The final products leaving the digestive system include food materials -- in particular indigestible fibre and bacteria. As food residue moves into the large intestine contractions force the contents towards the rectum. This movement initiates the defecation reflex which leads to the removal of waste through the anus.