Chapter 4 – Human Digestion and Absorption PDF

CHAPTER 4 – HUMAN DIGESTION AND ABSORPTION CHRIS COMSTOCK MS, RD, LN CHAPTER OUTLINE  The Human Body  Digestive System Overview  Mouth & Esophagus  Stomach  Small Intestine & Accessory Organs  Circulatory Systems  Large Intestine  When Digestion Goes Awry INTRO TO THE HUMAN BODY  The hu...

CHAPTER 4 – HUMAN DIGESTION AND ABSORPTION CHRIS COMSTOCK MS, RD, LN CHAPTER OUTLINE  The Human Body  Digestive System Overview  Mouth & Esophagus  Stomach  Small Intestine & Accessory Organs  Circulatory Systems  Large Intestine  When Digestion Goes Awry INTRO TO THE HUMAN BODY  The human body can be divided into many “systems” which all work together  Anatomy* = study of the STRUCTURE of the body  Physiology* = study of the FUNCTION of the body  In the human body, structure often determines function ORGANIZATION OF THE BODY  The human body is incredibly complex  Cells are the basis of the structure and function of the body  Groups of 1 type of cell = tissues  4 Main Tissue Types**: Epithelial, Connective, Muscle and Nervous Tissues  Groups of tissues = organs  Groups of organs = organ systems  Groups of organ systems = an organism! MORE ON THE HUMAN CELL  Cells are constantly producing new products and breaking down old substances  Cells need a constant supply of energy  Adenosine Triphosphate (ATP)*  ATP can be produced through two different pathways: an anaerobic pathway and an aerobic pathway.  In the aerobic pathway, oxygen is used to transform the energy-releasing nutrients (CHOs, fats, proteins) into ATP  Note: ATP is actually a storage form of energy – energy is released when the body breaks down/uses ATP  *The body needs a constant supply of ATP to do all of its work A FEW RELEVANT ORGAN SYSTEMS  Digestive*  Digests and absorbs nutrients and provides ALL the other systems of the body with nutrients  Cardiovascular*  Delivers nutrients from the digestive system to the rest of the body  Respiratory*  Provides oxygen to cells so they can use the nutrients to make ATP  Lymphatic*  Plays a role in immunity and is vital in the absorption of fats DIGESTION AND ABSORPTION  Digestion*  The mechanical or chemical breakdown of large ingested molecules into small absorbable molecules  Mechanical: Chewing, muscular movements of the tract (peristalsis, segmentation, churning, etc.)  Chemical: Digestive enzymes  Absorption*  The passage of digested molecules across the digestive tract into the inside of the body THE GASTROINTESTINAL TRACT  GI tract = The tube from the mouth to the anus  Everything inside this tube is EXTERNAL* to the human body until it is absorbed  This is important from an immune perspective as pathogens (disease-causing organisms such as bacteria, viruses, fungi, etc.) are kept “outside” while traveling through the GI tract  Digestion occurs within the tube  Absorption occurs across the tube DIGESTION AND ABSORPTION  Just because a nutrient is digested, does not mean it will get absorbed  It is possible to have trouble digesting foods (mechanically +/or chemically), while having a perfectly functioning absorptive process  Examples:  An individual with loose-fitting dentures might not be able to chew their food sufficiently  Elderly individuals often produce lower levels of stomach acid GASTROINTESTINAL SYSTEM OVERVIEW  Anatomy of the GI Tract  Know the sections and the sphincters!  GI Motility: Mixing and Propulsion  Part of the “mechanical digestion”  GI Secretions  Part of the “chemical digestion” THE HUMAN DIGESTIVE SYSTEM – 11:52  https://www.youtube.com/watch?v=s06XzaKqELk – Make sure you watch this video! THE FLOW OF DIGESTION**  Pre-Ingestion Digestive Processes  Marinating, tenderizing, slicing, mashing, cooking, etc. all begin the mechanical and chemical breakdown of foods!  Mouth  Salivary enzymes (chemical) and chewing (mechanical)  Esophagus  Mechanical digestion via peristalsis  Stomach  Stomach enzymes (chemical) and mixing (mechanical)  Small Intestine and Accessory Organs (Liver, Pancreas, and Gallbladder)  Intestinal enzymes and accessory organ enzymes (chemical), mixing, and peristalsis (mechanical)  Most digestion and absorption takes place in the small intestine  Large Intestine  Reabsorbing water and electrolytes  Rectum, Anus, and Excretion FUNCTIONS OF THE GI TRACT 1. Movement of food 2. Secretion of enzymes, hormones, acid, etc. to help break down food, lubricate its passage, aid in its absorption, kill microorganisms in the food…. 3. Digestion 4. Absorption 5. Elimination – getting rid of whatever is not absorbed at the other end 6. Nutrient Production – some nutrients are produced by bacteria living in the colon  Folate, vitamin K, biotin, and short-chain fatty acids** TERMS TO KNOW  Olfactory*  The sense of smell  Important in digestion because it stimulates salivary glands and other digestive processes  Saliva*  Watery substance made by salivary glands in the mouth – contains lubricants, enzymes* and lysozymes*  Mucus*  Thick substance made by mucous glands throughout the GI tract  Bolus*  What a swallowed “chunk” of food is called  Chyme*  What food is called after it becomes a soupy mess in the stomach  GI tract is about 15-20 feet from mouth to anus  Mouth  Esophagus  Stomach  S.I.  L.I.  Rectum  Anus  Mechanical Digestion:  Mouth (teeth), Esophagus (minimal, via peristalsis), Stomach (mixing and churning), S.I. (peristalsis and mixing movements)  Chemical Digestion:  Mouth (salivary enzymes and water), Stomach (stomach enzymes and water), Small Intestine (intestinal enzymes, accessory organ enzymes and water)  Absorption  Minimal in the stomach (mostly drugs, alcohol, some water, some vitamins or minerals)  Almost all absorption occurs in the Small Intestine!  Some water and electrolytes are reabsorbed in the Large Intestine SPHINCTERS/VALVES OF THE GI TRACT  Lower Esophageal Sphincter (Cardiac Sphincter)*  At the end of the esophagus/into the stomach  Pyloric Sphincter*  At the end of the stomach/into the S.I.  Sphincter of Oddi (Hepatopancreatic Sphincter)*  Controls where accessory organs dump into the S.I.  Ileocecal Valve*  At the end of the S.I./into the L.I.  Internal and External Anal Sphincter*  At the end of the anus/to the outside of the body FYI: TIME FRAMES THROUGH THE GI TRACT  Overall: ~24 hrs on average (varies widely)  Through the esophagus (~10 inches):