Chapter 22 - GI system

Chapter 22 GI - Chapter 21 Gastrointestinal System GI Organs Functions table 21.1 The main function of the digestive system is to transfer

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Chapter 21 – Gastrointestinal System GI Organs & Functions – table 21.1 The main function of the digestive system is to transfer nutrients, water, and electrolytes from ingested food into body’s internal environment. 4 functions: Motility: muscular contractions that mix and move contents forward of the digestive tract Secretion: transfer of digestive juices by exocrine glands into the digestive tract Digestion : chemical change (hydrolysis) of large molecules (e.g., carbohydrates, proteins, and fats) into their smaller subunits e.g. starch into glucose, proteins into amino acids, fats into fatty acids Absorption: passage of the products of digestion (e.g., glucose), along with water, vitamins and electrolytes into the blood and lymph We do not absorb starch, sugar, or protein Figure 20.1 – Four Digestive Processes Figure 20.2 - GI system Structures of the Gastrointestinal Tract Mouth, pharynx, and esophagus (pharynx is the back of the throat used for both respiration and food. The esophagus is only used for food.) Stomach Small intestine Colon Rectum and anus Layers of GI Tract Mesentery : -holds organs in place (blood vessels are go to liver) Mucosa Lines the lumen Contains lymph nodes (have pyers? patches to help trap some bacteria) Keeps lining greased Goblet cells : Secrete mucus Motility Functions of the GI Tract Movement of food through the GI tract. Ingestion : Taking food into mouth Mastication : .Chewing the food and mixing it with saliva (salivary amalyze) Deglutition : .Swallowing the food Peristalsis : Rhythmic wave-like contractions that move food through GI tract. The oral cavity 1
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Mastication by the teeth is the first step grinds and breaks the food into smaller pieces. mixes food with the saliva and stimulates taste buds Enzyme : salivary amylase chemically changes starch (first enzyme that acts on food) .Lysozyme in the saliva lyses bacteria. Saliva also keeps the mouth and teeth clean. Salivary secretion is continuous Salivary Glands 21.9 Saliva (not responsible for knowing these) Bicarbonate Mucus Salivary amylase Lysozyme Infection of this can cause Mumps. Esophagus Muscular tube from pharynx to stomach Upper 1/3 – skeletal muscle (cough up) Lower 2/3 – Smooth muscle (no control) Upper esophageal sphincter Skeletal muscle Between pharynx and esophagus Lower esophageal sphincter or Cardiac Sphincter Smooth muscle Between esophagus and stomach Swallowing Reflex figure 20.29 Bolus (lump of food) descends in pharynx, pressing in epiglottis *Epiglottis covers glottis so food does not enter trachea.
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This note was uploaded on 09/22/2009 for the course BIOL 2160 taught by Professor Kt during the Spring '08 term at LSU.

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Chapter 22 GI - Chapter 21 Gastrointestinal System GI Organs Functions table 21.1 The main function of the digestive system is to transfer

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