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Digestive System.docx

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Langara College
BIOL 1175

Digestive System What are the main steps in the digestive process? - Ingestion: intake of blood via the mouth - Digestion – mechanically or chemically break down food into their subunits - Movement – Food must be moved along the GI tract in order to fulfill all functions - Absorption – movement of nutrients across the GI tract wall to be delivered to cells/tissues via blood - Elimination – removal of indigestible molecules The digestive system Mouth -> Pharynx -> esophagus -> stomach -> small intestine -> large intestine -> rectum -> out via anus Layers of GI tract - Mucosa – innermost layer that produces mucus that protect the lining and also produce digestive enzymes - Submucosa – 2 ndlayer of loose connective tissue that contains blood vessels, lymphatic vessels and nerves (protection from bacteria from food we ingest) - Muscularis – 3 layer made of 2 layer of smooth muscle that move food along the GI tract - Serosa – outer lining that is part of the peritoneum that covers abdominal organs The Mouth - 3 Pairs of salivary glands secrete salivary amylase (an enzyme) that begins carbohydrate digestion - Tonsils (2^o lymph organ) at the back of the mouth and other lymphatic tissues are important in fighting disease - The tongue (a skeletal muscle) is covered in taste buds and also assists in mechanical breakdown and movement of food - Tongue forms a bolus (mass of chewed food) and moves it towards the pharynx (throat) Teeth- Function  Mechanical digestion – break food into smaller pieces o Incisors clip and slice o Canines puncture and tear o Molar and premolars crush o Teeth- Structure  Regions o Crown – above the gum o Root – below the gum  Layers o Pulp- innermost, with blood vessels and nerves (are alive) o Dentin – hard bone like o Enamel- nonliving, covers crown The small intestine is the most important structure in the digestive system not the stomach. The stomach - Stores food, start digestion of proteins, controls movement of chime into small intestine - J-shape organ with a thick wall - There are 3 layers of muscle in the muscularis layer of the stomach wall helping in the mechanical digestion and allowing it to stretch - mucosa layer has deep folds called rugae and gastric pits that lead into gastric glands that secretes gastric juice - gastric juice contains pepsin, and enzyme that breaks down proteins, and hydrochloric acid (HCl) and mucus. Gastric juice + food = chime - HCl gives the stomach a pH 2 very acidic, activates pepsin and helps kill bacteria in food What is Heartburn? - Acid from stomach passes into the esophagus (acid reflux) - burning sensation in esophagus - Chronic heartburn called gastroesphageal reflux disease could be brought by helicobacter pylori infection - some drug such as antacids, neutralize the stomach acid - avoid high fat meals, don’t overeat, eat several small meals, exercise lightly The small intestine - Averages 6m (18ft) - first section = duodenum, and is where liver/gallbladder/pancreas connect - Enzyme secreted by pancreas into the small intestine digest carbohydrates, proteins and fats - Bile is secreted by gallbladder into small intestine to emulsify fats - Digested food is abosorbed through very large surface area created by numerous villi (finger like projections) and microvilli Nutrients digested and transported out of the small intestine 1. Carbohydrate absorption 1. Protein absorption 2. Fat abs
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