Digestive System S24 PDF

The Digestive System Chapter 26 1  Learning outcomes 26.1 – Identify and describe the locations of digestive organs and mesenteries in the abdominal cavity 26.2 – Describe the structure and functions of the organs of the alimentary canal 26.3 – Compare and...

The Digestive System Chapter 26 1  Learning outcomes 26.1 – Identify and describe the locations of digestive organs and mesenteries in the abdominal cavity 26.2 – Describe the structure and functions of the organs of the alimentary canal 26.3 – Compare and contrast the microscopic anatomy of regions of the alimentary canal 26.4 – Trace the path of food through the alimentary canal 26.5 – Identify and describe the structures and functions of the accessory digestive organs 2  Overview of the Digestive System The alimentary canal (Gastrointestinal tract, digestive tract) Mouth, pharynx, and esophagus Stomach, small intestine, and large intestine (colon) Rectum and anal canal Accessory digestive organs Teeth, tongue, salivary glands Gallbladder, liver, and 3 pancreas Digestive processes 1. Ingestion 2. Propulsion (Motility) Swallowing, peristalsis 3. Mechanical and Chemical digestion 4. Absorption- nutrients and water 5. Defecation (Egestion) 4 Sources of nutrients Histology of the Alimentary Canal Wall 1. Epithelial lining 2. lamina propria 3. Muscularis mucosae 4. Submucosa 5. Submucosal nerve plexus 6. Circular muscle 7. Myenteric nerve plexus 8. Longitudinal muscle (muscularis externa) 9. Serosa vs. adventitia vs. both How do these layers differ throughout the GI tract? 26.3 6  Nervous control of the gut Intrinsic- Enteric Nervous System Sensory neurons that monitor tension, and efferent visceral motor fibers. OWN SYSTEM! Can function in absence of extrinsic nervous system Myenteric-GI motility control - Stimulatory influences  tonic contraction (tone)  contraction frequency / intensity ( propulsion) Sphincter tone Submucosal plexus Secretion Absorption Contraction of muscularis mucosa Extrinsic- ANS (sympathetic & parasympathetic) 7 Peritoneum and Mesenteries Parietal vs. Visceral peritoneum Peritoneal cavity Intraperitoneal vs. retroperitoneal Mesenteries Greater omentum Lesser omentum Mesentery proper Falciform ligament The mouth and salivary glands The pharynx and esophagus Esophageal Hiatus  The Stomach J-Shaped Organ, Inferior to Diaphragm Functions: Storage Digestion (Mechanical & Chemical) Protein digestion Begins here Absorption of Water, Alcohol, Drugs Food enters as bolus (food & saliva) Leaves as chyme (partially digested food & gastric juices) Wall Modifications: Rugae Oblique Muscle in Muscularis  Gastric pits and glands Gastric Glands in Mucosa Mucous Cells (Protective Coating) Parietal Cells (HCl, pH = 2) Chief Cells Pepsinogen (Pepsinogen + HCl Pepsin) Enteroendocrine cells G Cells (Gastrin stimulates parietal & Chief Cells) 14 Which statement about the stomach is FALSE? A – The labeled region is the fundus B – The lesser omentum attaches to the lesser curvature C – Parietal cells secrete HCl D – The stomach performs mechanical breakdown and digestion E – The distal end of the stomach connects to the 26.2 ileum  The Small Intestine Site of Most Chemical Digestion Site of 90% of Absorption Monosaccharides Blood Amino Acids Blood Fatty Acids & Glycerol Lymph The Small Intestine 3 Subdivisions: Duodenum First 10-12” Secretes digestive enzymes Receives bile from Liver (via bile duct) Receives pancreatic juice (via pancreatic duct) Jejunum –Middle Length Ileum – Last, Joins with Large Intestine at Ileocecal Valve  The Small Intestine – Microscopic Anatomy Modifications for absorption increase surface area (200 sq. meters!) Circular folds (plicae circulares); 1 cm tall Villi – finger-like projections of the mucosa Covered with simple columnar epithelium Velvety texture; 1 mm tall; contain capillaries and absorptive cells (enterocytes) Microvilli – apical surface of absorptive cells further increase surface area for absorption and contain digestive enzymes to complete digestion of foods (“brush border enzymes” act on all classes of food) 18 Absorbing Nutrients  What statement about the small intestine is FALSE? A – The duodenum receives fluids from the liver and pancreas B – The order of the regions of the small intestine is duodenum, jejunum, and ileum C – Circular folds are ridges of mucosa and submucosa D – Microvilli are found on the basal layer of the simple columnar ET E – The small intestine is the site of virtually all absorption in the GI 26.2 tract  Which statement about the large intestine (colon) is FALSE? A – The descending colon is found in the right lumbar region B – The ileocecal valve prevents feces from backing up into the ileum C – The internal anal sphincter is under autonomic control D – The line is pointing to the rectum E – Simple columnar epithelium is found within the 26.2 large intestine  How does food pass through the alimentary canal? Start with the mouth and end with the anus What organs does food pass through in between? What main sub-structures are found in each organ that food passes through? What sphincters / valves between organs does the food pass through? What happens to the food as it passes through each organ (i.e. what are the functions of the organ?)? 26.4 Describe the function of the accessory digestive organs/structures 26.5 Hormone Origin (Secreted Target Effects from) Gastrin Cholecystokinin (CCK) Secretin Gastric Inhibitory 26.2 Peptide (GIP) 26.5 CCK and Secretion – targets and effects