Chapter 23 The Digestive System Copyright 2006

Chapter 23 The Digestive System Copyright © 2006 Pearson Education, Inc. , publishing as Benjamin Cummings

Objectives: § Functional anatomy of the digestive system § Gross and microscopic anatomy of the digestive system organs § Composition of gastric juice § Rregulation of the digestive juice secretions § Mechanical and chemical digestive processes § Absorption § Neural, mechanical, and hormonal control of gastrointestinal processes. Copyright © 2006 Pearson Education, Inc. , publishing as Benjamin Cummings

Organs of the Digestive System § Falls into two main groups: § § § The alimentary canal organs Accessory digestive organs Alimentary canal (GIT): § Includes: § § Mouth, pharynx, esophagus Stomach, small intestine, and Large intestine Involves: § Breakdown of food § Nutrient absorption into blood Copyright © 2006 Pearson Education, Inc. , publishing as Benjamin Cummings

Accessory digestive organs: § Teeth, tongue (in oral cavity) § Gallbladder & large digestive glands (outside GIT) § Large glands include: § § Liver § § Salivary glands Pancreas Contribute to mechanical & chemical breakdown of food Copyright © 2006 Pearson Education, Inc. , publishing as Benjamin Cummings

Copyright © 2006 Pearson Education, Inc. , publishing as Benjamin Cummings Figure 23. 1

Digestive Process § The GIT: § § Nutrients: § § A “disassembly” line More available to the body in each step There are six essential activities: § § § Ingestion (food taking) Propulsion (swallowing, peristalsis) Mechanical digestion (chewing, churning, segmentation) Chemical digestion (enzymatic catabolism) Absorption (blood or lymph) Defecation (indigested substances) Copyright © 2006 Pearson Education, Inc. , publishing as Benjamin Cummings

Copyright © 2006 Pearson Education, Inc. , publishing as Benjamin Cummings Figure 23. 2

Gastrointestinal Tract Activities § Ingestion: § § Taking food into the digestive tract Propulsion: § Swallowing and peristalsis § § Peristalsis: contraction & relaxation waves of muscles in the organ walls (Name organs) Mechanical digestion: § Chewing, churning, and segmentation § Name organs involved in each activity Copyright © 2006 Pearson Education, Inc. , publishing as Benjamin Cummings

Peristalsis and Segmentation Compare and contrast between the two movements? Copyright © 2006 Pearson Education, Inc. , publishing as Benjamin Cummings Figure 23. 3

Gastrointestinal Tract Activities (cont’d) § Chemical digestion: § § Starts in the mouth § § Enzymatic breakdown of food into building blocks Completes in the small intestine Absorption: § § Nutrients movement from GIT into blood or lymph Defecation: § Elimination of indigestible solid substances Copyright © 2006 Pearson Education, Inc. , publishing as Benjamin Cummings

Regulation of Digestion § Involves: § Mechanical and chemical stimuli § Extrinsic control by CNS centers § Intrinsic control by local centers Copyright © 2006 Pearson Education, Inc. , publishing as Benjamin Cummings

Receptors of the GI Tract § Mechano- and chemoreceptors: § Located: § § In the walls of the GI tract organs Respond to: § § § Stretch (food), osmolarity (solute concn. ), and p. H Presence of substrates & end products of digestion They initiate reflexes that: § Activate or inhibit digestive gland secretions (enzymes in lumen & hormones in blood) § Stimulate smooth muscles of the GIT (mix lumen contents & move them along the tract) Copyright © 2006 Pearson Education, Inc. , publishing as Benjamin Cummings

Nervous Control of the GI Tract § Many of the controlling systems of the digestive tract are intrinsic –in house- involving: § § § Nerve plexuses, or Hormone-producing cells Gut brain: § Network of enteric nerve plexuses § Found between the muscle layers in the al. canal wall § Spread along the entire length of the tract § Influence each other in & the same or different organs of the digestive tract Copyright © 2006 Pearson Education, Inc. , publishing as Benjamin Cummings

Types of Resulting Relex Activities § Short reflexes: § § § Occurs n response to locally arising stimuli Mediated entirely by local enteric (gut) plexuses Long reflexes: § § Initiated by stimuli arising inside or outside the GI tract Involve CNS centers and extrinsic autonomic nerves (vagus) Copyright © 2006 Pearson Education, Inc. , publishing as Benjamin Cummings

Nervous Control of the GI Tract Copyright © 2006 Pearson Education, Inc. , publishing as Benjamin Cummings Figure 23. 4

Histology of the Alimentary Canal § The walls (esoph. to anal) have the same four tunics § From lumen outward, layers include: § § Submucosa § Muscularis externa § § Mucosa Serosa Each tunic has: § A predominant tissue type § A specific digestive function Copyright © 2006 Pearson Education, Inc. , publishing as Benjamin Cummings

Histology of the Alimentary Canal Copyright © 2006 Pearson Education, Inc. , publishing as Benjamin Cummings Figure 23. 6

Mucosa § Consists of three layers: § § Lamina propria § § Lining epithelium Muscularis mucosae Three major functions: § Secretion of mucus § Absorption of end products of digestion § Protection against infectious disease Copyright © 2006 Pearson Education, Inc. , publishing as Benjamin Cummings

§ Epithelial lining of mucosa: § § § Simple columnar, and mucus-secreting goblet cells Stomach and small intestine mucosa contain: § § Enzyme-secreting cells Hormone-secreting cells (endocrine and digestive organs) Copyright © 2006 Pearson Education, Inc. , publishing as Benjamin Cummings

Other Sublayers § Submucosa: § Dense connective tissue containing: § § Elastic fibers, blood & lymphatic vessels, lymph nodes, and nerves Muscularis externa: § § Inner circular & outer longitudinal muscle layers Rresponsible for segmentation & Peristalsis § Serosa: § Protective visceral peritoneum (intraperitoneal organs) Retroperitoneal organs: § § Not surrounded by peritoneum (with both serosa & adventitia) Copyright © 2006 Pearson Education, Inc. , publishing as Benjamin Cummings

Oral Cavity and Pharynx: Copyright © 2006 Pearson Education, Inc. , publishing as Benjamin Cummings Figure 23. 7 b

Salivary Glands § Produce and secrete saliva that: § Cleanses the mouth § Dissolves food chemicals (taste) § Moistens food & aids in bolus formation § Contains enzymes that begins breakdown of starchy food Copyright © 2006 Pearson Education, Inc. , publishing as Benjamin Cummings

Salivary Glands § Extrinsic glands (three pairs): § Located outside the oral cavity , but § Empty their secretion into the oral cavity § Include: § § Submandibular § § Parotid Sublingual Intrinsic glands (buccal glands): § Scattered throughout the oral mucosa Copyright © 2006 Pearson Education, Inc. , publishing as Benjamin Cummings

Salivary Glands § Parotid: § § § Anterior to the ear between the masseter muscle and skin Duct opens into the vestibule next to second upper molar Submandibular: § § § Along the medial aspect of the mandibular body Ducts open at the base of the lingual frenulum Sublingual: § Anterior to the submandibular gland & under the tongue § Opens via 10 -12 ducts into the floor of the mouth Copyright © 2006 Pearson Education, Inc. , publishing as Benjamin Cummings

Salivary Glands Copyright © 2006 Pearson Education, Inc. , publishing as Benjamin Cummings Figure 23. 9 a

Saliva: Source and Composition § Secreted by serous & mucous cells of salivary glands § 97 -99. 5% water § Hypo-osmotic § Slightly acidic solution containing: § Electrolytes: (Na+, K+, Cl–, PO 42–, HCO 3–) § Digestive enzyme: Salivary amylase & lingual lipase § Proteins: Mucin, lysozyme, defensins, and Ig. A § Metabolic wastes: Urea and uric acid Copyright © 2006 Pearson Education, Inc. , publishing as Benjamin Cummings

Peritoneum and Peritoneal Cavity § Peritoneum: § Serous membrane of the abdominal cavity § Visceral: § § Parietal: § § Covers external surface of most digestive organs Lines the body wall Peritoneal cavity: § Potential cavity between the two layers § Contains slippery fluid secreted by serous membranes § Lubricates digestive organs easing sliding across one another Copyright © 2006 Pearson Education, Inc. , publishing as Benjamin Cummings

Peritoneum and Peritoneal Cavity Copyright © 2006 Pearson Education, Inc. , publishing as Benjamin Cummings Figure 23. 5 a

Peritoneum and Peritoneal Cavity § Mesentery: § A double layer of peritoneum § Provides vascular and nerve supply to the viscera § Holds digestive organs in place § § Retroperitoneal organs: § § Stores fat Organs outside the peritoneum (during development) Peritoneal (intraperitoneal) organs : § Organs surrounded by peritoneum Copyright © 2006 Pearson Education, Inc. , publishing as Benjamin Cummings

Pharynx § Three parts: § § § Naso pharynx (no role in digestion) Oro- and laryngopharynx (food pass thru) Lined with: § § § Stratified squamous epithelium (protective) Mucus glands Has two skeletal muscle layers § Inner longitudinal § Outer pharyngeal constrictors § They propel food to esophagus Copyright © 2006 Pearson Education, Inc. , publishing as Benjamin Cummings

Esophagus § Muscular tube extending from laryngopharynx to stomach § Pierces the diaphragm to the abdomen at the esophageal hiatus § § Joins the stomach at the cardiac orifice A gastroesophageal (cardiac )sphincter (physiological) surrounds the cardiac orifice § Mucosa is a nonkeratinized stratified squamous epith. § Glands secrete mucus as the bolus moves through Copyright © 2006 Pearson Education, Inc. , publishing as Benjamin Cummings

Esophagus Copyright © 2006 Pearson Education, Inc. , publishing as Benjamin Cummings Figure 23. 12