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Overview of the Digestive System Digestive Tract: Mouth, pharynx, and esophagus, stomach, small intestine, and large intestine (colon) Accessory Organs: Teeth, tongue, salivary glands, pancreas, liver, and gallbladder Functions of the Digestive System • Ingestion • Mechanical processing • Chemical digestion • Secretion • Absorption • Excretion Histology of the Digestive Tract Mucosa Submucosa Muscularis Externa Serosa Mucosa (Innermost Layer) • Epithelium • Connective • Tissue (Blood vessels, lymphatic vessels, lymphatic nodules) Smooth Muscle Submucosa Connective tissue • • • • Blood vessels Lymphatic vessels Nerve plexus May have glands and lymphatic tissue Muscularis Externa Smooth or Skeletal Muscle If smooth muscle, usually 2 layers (circular and longitudinal) Adventitia or Serosa Adventitia (organs superior to diaphragm) Serosa = visceral peritoneum Small Intestine: Peyer’s Patches Components of the Digestive System GI Tract: •Oral Cavity •Pharynx •Esophagus •Stomach •Small Intestine •Large Intestine Oral Cavity Oral Cavity The Pharynx • Nasopharynx • Oropharynx • Laryngopharynx The Esophagus The Esophagus • Stratified • • squamous epithelium Mucous glands Muscularis externa – skeletal muscle first third of length Peristalsis in Esophagus LE 21-8 Muscles contract Bolus of food Muscles contract, constricting passageway and pushing bolus down Muscles relax Muscles relax, allowing passageway to open Stomach Muscles contract Muscles relax Stomach • Site where • food is churned into chyme Protein digestion begins Stomach Stomach Stomach – Microscopic Anatomy Stomach – Microscopic Anatomy The Stomach – Microscopic Anatomy Ulcers in stomach Helicobacter pylori Small Intestine – Gross Anatomy • Longest portion of • • the alimentary canal Site of most enzymatic digestion and absorption Three subdivisions • Duodenum, jejunum, and ileum LE 21-11a Duodenum and Related Organs Liver Bile Gallbladder Stomach Bile Acid chyme Intestinal enzymes Duodenum of small intestine Pancreatic juice Pancreas Duodenum and Related Organs Enzymes in Small Intestine Small Intestine – Microscopic Anatomy LE 21-11b Lumen of intestine Nutrient absorption Vein with blood en route to the liver Nutrient absorption into epithelial cells Microvilli Epithelial cells Muscle layers Amino acids and sugars Lumen Fats Blood capillaries Large circular folds Blood Villi Lymph vessel Lymph Nutrient absorption Epithelial cells Villi Intestinal wall Fatty acids and glycerol Small Intestine: Duodenum Br = Brunner glands V = Villus G = Goblet cells Cr = Intestinal glands MM = Muscularis Mucosae LP = Lamina Propria The Small Intestine – Structural Features Gross Anatomy of Large Intestine •Cecum •Appendix •Ascending •Transverse •Descending •Sigmoid colon •Rectum •Anus LE 21-12 Large intestine (colon) Small intestine Sphincter End of small intestine Rectum Anus Nutrient flow Appendix Cecum Gross Anatomy of Large Intestine • Rectum – descends along the inferior half of the • sacrum Anal Canal – the last subdivision of the large intestine Gross Anatomy of Large Intestine Microscopic Anatomy of Large Intestine • • • • • Villi are absent Contains numerous goblet cells Intestinal crypts – simple tubular glands Lined with simple columnar epithelial tissue Epithelium changes at anal canal • Becomes stratified squamous epithelium Microscopic Anatomy of Large Intestine Teeth Salivary Glands Pancreas Exocrine Pancreas: Histology Liver • • • • Largest gland in the body Performs over 500 functions Digestive function – bile production Performs many metabolic functions Visceral Surface of the Liver Microscopic Anatomy of Liver Microscopic Anatomy of Liver Gallbladder • Stores and concentrates bile • Expels bile into duodenum • Bile emulsifies fats Gallbladder Enzymes in Small Intestine The Peritoneal Cavity and Peritoneum • Mesentery – a double layer of peritoneum • Holds organs in • • place Sites of fat storage Provides a route for circulatory vessels and nerves Mesenteries • Superficial view of the abdominal organs Mesenteries • Greater omentum and transverse colon reflected Mesenteries • Sagittal section through the abdominopelvic cavity Segmentation • • Rhythmic local contractions of the intestine Mixes food with digestive juices Disorders of the Digestive System • Intestinal obstruction • Mechanical obstructions • Adhesions, tumors, or foreign objects • Nonmechanical obstruction • Halt in peristalsis • Trauma • Intestines touched during surgery Disorders of the Digestive System • Inflammatory bowel disease • Inflammation of intestinal wall • Crohn’s disease • Ulcerative colitis • Viral hepatitis – jaundice and flu-like symptoms • Major types – A, B, C, and G • Cystic Fibrosis and the Pancreas The Digestive System in Later Life • • Middle age – gallstones and ulcers Old age – activity of digestive organs decline • • • • Fewer digestive juices and enzymes produced Absorption is less efficient Dehydration of fecal mass leads to constipation Diverticulosis and cancer of digestive organs