Digestion PDF

Digestion Digestive System Basics Faculty of Science | Department of Biochemistry The Digestive System – Basics Five basic chemical tastes Sweet, sour, bitter, salty, and umami or savoury Sweet, salty, and fatty foods...

Digestion Digestive System Basics Faculty of Science | Department of Biochemistry The Digestive System – Basics Five basic chemical tastes Sweet, sour, bitter, salty, and umami or savoury Sweet, salty, and fatty foods Almost universally desired Can lead to drastic overeating of these substances Faculty of Science | Department of Biochemistry The Digestive System – Basics Digestive tract Flexible, muscular tube Extends from the mouth through the throat, esophagus, stomach, small intestine, large intestine, and rectum to the anus Total length about 8 metres Body surrounds digestive canal Primary role To digest food to its components, absorb, and excrete Faculty of Science | Department of Biochemistry The Digestive System Faculty of Science | Department of Biochemistry Chewing and swallowing Salivary glands add water, minor digestive enzymes (for starch and fat), antimicrobial components, mucus – to form a smooth food bolus The teeth crush food to increase the surface area, open up seeds, hulls, etc. © Human Biology Belk and Borden Faculty of Science | Department of Biochemistry Swallowing co-ordination affected by diseases of the nervous system (e.g. Alzheimer’s, Parkinson’s), stroke, prematurity, etc. Faculty of Science | Department of Biochemistry The Digestive System Mechanical digestion Begins in the mouth; aided by chewing, saliva Stomach and small intestine Peristalsis helps to liquefy food Chyme/digesta help to create a paste-like substance Faculty of Science | Department of Biochemistry The Muscular Stomach Faculty of Science | Department of Biochemistry Up next…  Digestion Key Digestion Factors Impacting Nutrient Absorption Faculty of Science | Department of Biochemistry Chemical Digestion Digestive juices are secreted by salivary glands, stomach, pancreas, liver, and small intestine Digestive juices contain enzymes that break down nutrients Digestion begins in the mouth Saliva contains enzymes that break down Starches (salivary amylase) Fats (lingual lipase) Faculty of Science | Department of Biochemistry The Digestive System Protein digestion begins in the stomach Gastric juices (water, enzymes, hydrochloric acid) are required to activate the protein-digesting enzyme (pepsin) Acid strength is determined by its pH Faculty of Science | Department of Biochemistry pH Values of Digestive Juice and Other Common Fluids Faculty of Science | Department of Biochemistry Pyloric Sphincter – Separating Sections of the Digestive System Faculty of Science | Department of Biochemistry The healthy digestive system is capable of adjusting to almost any diet and can handle any combinations of food with ease. Within 24 to 48 hours, 90 percent of carbohydrate, fat, and protein are digested and absorbed. The rate at which nutrients are absorbed depends on many factors: the form of the nutrient in a food other nutrients or components within the food The body’s need for the nutrient The health of the GI tract Faculty of Science | Department of Biochemistry The Digestive System Small intestine The organ of digestion and absorption Secretes the following fluids to aid in digestion: Bile: Emulsifier, made by the liver, stored in the gallbladder Pancreatic juice: Secreted by the pancreas, contains an acid-neutralizing agent Faculty of Science | Department of Biochemistry Absorption and Transportation of Nutrients Absorption Nutrient molecules traverse intestinal lining cells Cells absorb nutrients and deposit in blood (carbohydrate, protein, minerals, most vitamins) and lymph (fat, some vitamins) The cells of the small intestine are selective, increasing absorption of some nutrients that may be in short supply Faculty of Science | Department of Biochemistry Details of the Small Intestinal Lining The cells of the intestinal tract lining are arranged in sheets that poke out into millions of finger- shaped projections (villi). Every cell on every villus has a brush-like covering of tiny hair-like projections (microvilli) that can trap the nutrient particles. Each villus (projection) has its own capillary network and a lymph vessel so that nutrients move across the cells. Faculty of Science | Department of Biochemistry Absorption and Transportation The digestive system is sensitive to malnutrition Severe undernutrition will result in the shrinking of the absorptive surface of the small intestine This causes impaired digestion, and the impaired digestion worsens malnutrition Large Intestine Absorbs water A few nutrients/metabolites are absorbed in the colon from bacterial activity Faculty of Science | Department of Biochemistry A Notice from Your Digestive Tract The body’s response to: Eating or drinking too fast = hiccups, choking Eating or drinking too much = heartburn, GERD Treatment with antacids or acid reducers may aggravate the problem Other digestive disturbances include constipation and diarrhea Faculty of Science | Department of Biochemistry Practical Example: The Digestion of a Sandwich