Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings CV Quiz

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Digestive System  Function and processes of the digestive system  Anatomy of the digestive system  Motility  Secretion  Regulation of GI function  Digestion and absorption

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Digestive System  The gastrointestinal tract is a long tube passing through the body that opens to the outside world on both ends. Thus, the contents can be considered to be part of the external environment.  The primary function is to move nutrients, water, and electrolytes from the external environment into the body’s internal environment  The food we eat is in the form of macromolecules that must be broken down. The digestive system secretes enzymes to break down food.

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings 5 Basic Processes of the Digestive System 1.Digestion: Mechanical and chemical breakdown of foods into units that can be taken across the intestinal epithelium into the body. 2.Absorption: Active or passive transfer of substances from the lumen of the GI tract to the extracellular fluid. 3.Motility: Movement of material in the GI tract as a result of muscle contraction. 4.Secretion: Both the transepithelial transfer of water and ions from the ECF to the digestive tract lumen and the release of substances synthesized by the GI epithelial cells. 5.Immune: Repelling foreign invaders via gut-associated lymphoid tissue (GALT). 80% of lymphocytes found in small intestive.

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Basic Processes of the Digestive System Figure 21-1

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 21-2a Digestive System Anatomy Oral cavity  esophagus  stomach  small intestine  large intestine  rectum

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Digestive System Anatomy  Mouth and pharynx  Mechanical and chemical digestion (secretion of saliva by salivary glands)  Esophagus  Stomach  Fundus (top)  body  antrum  Mechanical and chemical digestion: Mixing food and acid and enzymes to create chyme.  Pyloric valve  Lets out only small amount of chyme at a time, regulated by integrated signals and feedback loops between the intestines and stomach.  Small intestine  Duodenum (25cm)  jejunum  ileum  Most digestion and absorption takes place here via intestinal enzymes and exocrine secretions from the liver and pancreas (which enter the duodenum via ducts)  Accessory organs: pancreas and liver  Large intestine: colon and rectum  About 1.5L/day of the 7L/day of chyme generated ends up entering the colon.  Water and electrolytes are absorbed out of the chyme and into the ECF to make feces.  Anus

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Digestive System Anatomy: 4 Layers of GI Tract Wall 1.Mucosa (Inner Layer)  Epithelial cells  Lamina propria (connective tissue and immune cells)  Muscularis mucosae (thin layer of smooth muscle)  Modifications increase surface area 2.Submucosa (connective tissue, nerves, blood and lymph vessels) 3.Muscularis externa  Smooth muscle in layers  Nerves 4.Serosa (Outer Layer)  Connective Tissue

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Digestive System Anatomy: Folds of GI Tract  Entire wall folds  Rugae in the stomach  Plicae in the small intestine  Mucosal folds  Intestinal Villi project into the lumen  Tubular Invaginations of the Surface  Gastric Glands in the stomach  Crypts in the intestine

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 21-2c Digestive System Anatomy

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 21-2e Digestive System Anatomy Animation: Digestive System: Anatomy Review: Overall Function of the GI System PLAY

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Epithelial Cells  The type changes from section to section.  4 Epithelial Cell Types 1.Transport Cells:  Move water and ions into and out of the lumen and absorb nutrients from lumen. 2.Endocrine  Release hormones 3.Secretory Cells  Release enzymes, mucus, and paracrine molecules into the lumen 4.Stem  Create new cells

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Motility: For Mixing and Movement of Food  Tonic contractions  Sustained  Smooth muscle sphincters and stomach  Phasic contractions  Last a few seconds  Peristalsis moves bolus forward  Segmentation mixes

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 21-4a Contractions in the GI Tract

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Motility Figure 21-4b Animation: Digestive System: Motility PLAY

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 21-5 Secretion Daily mass fluid balance in digestive system

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 21-6 Acid Secretion by Parietal Cells

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 21-8 Neutralizing Bicarbonate Secretion in Duodenum: From Pancreas and Duodenal Cells

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 21-9 Secretion Cl – secretion by intestinal colonic crypt cells

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Secretion  Digestive enzymes secreted into mouth, stomach and intestine  Mucous cells in stomach and goblet cells in intestine: Protective of the lining  Saliva is an exocrine secretion with digestive enzymes.  Liver secretes bile. Gallbladder stores the bile until needed for digestion:  Bile salts act as detergents to solubilize fats, facilitating enzymatic fat digestion Animation: Digestive System: Secretion PLAY

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Regulation of GI Function  Long reflexes integrated in CNS  Short reflexes integrated in Enteric Nervous System (ENS)  Intrinsic neurons of the two nerve plexuses of the digestive tract lie completely w/in the wall of the gut. They carry out reflexes that are independent of control from the CNS  Reflexes involving GI peptides (Hormones, Neuropeptides and Cytokines)

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Sensory receptors and neurons Local stimulus Neurons of myenteric and submucosal plexuses Inter- neurons Sympathetic and parasympathetic neurons Enteric nervous system “The little brain” (pH, stretch, osmolarity, products of digestion) The cephalic brain External stimulus (sight, smell, etc.) Sensory receptors Smooth muscles or secretory cells Effectors Muscle contraction/relaxation Exocrine secretion (enzymes, mucus, acid, bicarbonate), Paracrines Endocrine secretions Digestive system responses Short reflexes Long reflexes KEY Stimulus Integrating center Receptor Efferent pathway Tissue response or Regulation of GI Function Integration of long and short reflexes in the digestive system Figure 21-11

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings REGULATION OF GI FUNCTION  Cephalic Reflexes: long reflexes that originate completely outside the digestive system. The smooth muscle and glands of the GI tract are under autonomic control. In general, parasympathetic neurons to the GI tract are excitatory and sympathetic are inhibitory.  Feedforward Reflexes  Begin with stimuli such as the sight, smell, sound, or thought of food.  Prepare the digestive system for food (mouth watering, movement of the stomach)  Emotional Reflexes  Psychologically induced diarrhea  Butterflies in your stomach

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure Regulation of GI Function Reflexes involving GI Peptides