Chapter Three; The Basics of Digestion
Chapter Three; The Basics of Digestion BIO 1050
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This 5 page Class Notes was uploaded by Amber Notetaker on Friday September 23, 2016. The Class Notes belongs to BIO 1050 at Wright State University taught by Amy Wissman in Fall 2016. Since its upload, it has received 10 views. For similar materials see Biology of Food in Biology at Wright State University.
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Date Created: 09/23/16
Chapter Three Digestion Functions of the Digestive System o 1. Ingestion-intake of nutrients o 2. Digestion- the physical and chemical breakdown of large molecules (of food) into smaller absorbable molecules o 3. Absorption- the movement of these small nutrient molecules across the cell membrane of cells lining the digestive track o 4. Elimination What makes eating so enjoyable? o Hunger and thirst Physical needs- drive how much and how often we eat o Appetite: unreliable (psychological) What is Digestion? o Digestion: processes of breaking down food into absorbable components o Gastrointestinal (GI) track consists of: Mouth, Pharynx Esophagus Stomach Small intestine Large intestine Accessory Organs: Salivary glands, liver& gall bladder and pancreas. Digestion is mechanical and Chemical o Mechanical Digestion: breaks down large food molecules to smaller molecules Chewing, grinding food (mouth) Churning (stomach) Peristalsis: the forward, rhythmic muscular contraction that moves food forward through the GI track. Segmentation in intestines (mixes) o Chemical Digestion: Digestive juices and enzymes break down food into absorbable nutrients Enzymes- proteins, specific shape, speeds up reaction (catalyzed), can break bones of food molecules, reused. Digestion Allows Us to Absorb Nutrients from Foods After digestion, nutrients are absorbed through the walls of the intestines into the body’s two transport systems: Circulatory system- blood Lymphatic system- lymph fluid o Send to the liver for processing before delivery to the body’s cells. o GI track is highly efficient: 92-97% of nutrients from food are digested and absorbed. What happens in the individual organs of the digestive system? o Mouth: breakdown of food begins in the mouth. Mastication- mechanical digestion. Saliva- chemical digestion Water, electrolytes, mucus and enzymes Salivary amylase, lipase ‘Bolus’ (food mass)- moves into pharynx, is swallowed, and enters the esophagus. o Epiglottis: prevents food from entering the trachea when you swallow. o Esophagus: Peristalsis Lower Esophageal Sphincter (LES): Connects the bottom of the esophagus to the top of the stomach (Cardiac Sphincter) LES then closes to prevent backflow of hydrochloric acid (HCI) from stomach o “Reflux” of stomach acid causes “heartburn” o Stomach: stores, mixes and prepares food Mechanical action: churning mixes food with digestive juices for several hours 2 Chemical Digestion- digestive secretions (enzymes, hormones HCI) “Chime”: Simi-liquid substance of partially digested food and digestive juices Pyloric sphincter: located between the stomach and small intestine, allows about 1 tsp of chime to enter the small intestine every 30 seconds Prevents backflow of intestinal content. Liquids, carbohydrates, low-fiber and low-calorie foods exit stomach faster. High fiber, fat and protein foods exit slower, keep you feeling full longer. Any absorption? Not much, liquids and aspirin o Small Intestine: Long, narrow, coiled Most Digestion and Absorption occur in the small intestine Three Segments: Duodenum Jejunum Ileum (inside) Interior surface area tremendously increased by circular folds, villi, and microvilli. o Large Intestine: absorbs water and some nutrients Ileocecal Sphincter: at ileum/ cecum juncture, Prevents backflow of waste matter into ileum LI Sections 1. Cecum 2. Colon (asc, transv, desc, sigmoid) 3. Rectum Very little digestion Bacterial action on remaining waste* Fiber and undigested carbohydrates Some vitamins produced Absorption of those vitamins, electrolytes and water Waste forms stool/ feces 3 Stored until eliminated o Appendix Vestigial organ/tissue o Accessory Organs Liver Produces: bile- needed for fat digestion Detoxifies Stores nutrients or releases them to bloodstream Gallbladder: Stores Bile Releases bile into small intestines when fat is ingested. Pancreas Secrets: Sodium bicarbonate: neutralizes acidic chime, protects enzymes from inactivation by acid. Digestive enzymes. Amylase: digests carbohydrate (starch) Lipase: digests fats Proteases: digestive protein o Trypsin, chymotrypsin, and carboxypeptidase Secretions and Functions of the GI (copied from HW) o Stomach Secretes hydrochloric acid (HCI) Secretes the hormone gastrin Secretes intrinsic factor o Gallbladder Concentrates and stores bile o Liver Produces bile o Pancreas Produces amylase Produces glucagon Produces insulin Produces pancreatic lipase Carbohydrate, Protein and Fat Digestive Enzymes 4 o Salivary Glands Salivary amylase o Stomach Pepsin Gastric lipase o Pancreas Chymotrypsin Trypsin Pancreatic Lipase Carboxypeptidase Pancreatic amylase o Small Intestine Lactase Common Digestive Disorders o Stomach Gastroenteritis Peptic o Small Intestine: Lactose Intolerance Deficiency of enzyme lactase Celiac disease Autoimmune disorder, inability to digest gluten protein. Malabsorption disorder o Example Question o Amylase- starch o Sucrose-sugar o Lipase o Pepsin-protein 5
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