PNB 2275 1st Edition Exam #3 Study GuideLecture 11. Basics of Digestion- The chewed food mixed with saliva is called bolus- The bolus moves to the stomach to become processed and turned into chyme- The digestive organs are grouped into the Gastrointestinal tract (GI tract)- The GI tract is composed of the oral cavity, pharynx, esophagus, stomach, small intestine, and large intestine.- Accessory digestive organs assist in the GI tract digestion of material; they include the teeth, tongue, salivary glands, liver, gallbladder, and pancreas.- Mechanical digestion physically breaks down ingested materials and chemical digestion breaks down ingested materials into smaller molecules by using enzymes- Propulsion moves food through the GI tract- These two movements are Peristalsis and Segmentation- Peristalsis is the process of muscular contraction that forms ripples along part of the GI tract andforces material to move further along the tract.- Segmentation helps disperse the material being digested and combine it with digestive organ secretions. - Secretion is the process of producing and releasing mucin or fluids such as acid, bile, and digestive enzymes. - Absorption involves either passive movement or active transport of electrolytes, digestion products, vitamins, and water across the GI tract epithelium, and into the GI tract blood and lymph vessels. - Lastly we have Elimination which is the body getting rid of wastes through compacted feces by the process of defecation.- 6 digestive functions: Ingestion > Mechanical Processing > Digestion > Secretion > Absorption > Excretion2. Serous Membranes of the Abdominal Cavity- Peritoneum - Parietal Peritoneum: inside the surface of the body wall- Visceral Peritoneum: surface of the internal organs- Peritoneal fluid- produced by serous membrane- provides essential lubrication allowing sliding without friction or irritation3. Histology of GI tract- Duodenum and Jejunum have villi to increase surface area- Indentations in the stomach are called gastric glands and in the small intestine they are called crypts- Rugae are the folding’s in the stomach- Mucosa: most inner facing the lumen- Most inner portion is the musical epithelium - Most variable feature in GI - Enterocytes (breaking down of nutrients into the cell) - Endocrine (release hormone into blood) - Exocrine (out into the rumen)- Lamina Propria – connective tissue which contains nerve fibers, vessels, and lymph nodes, wandering immune cells as well- Muscularis Mucosae – thin layer of smooth muscle (last layer) moves the villi- Submucosa: connective tissue layer containing larger blood and lymph vessels- Submucosal plexus is a nerve supply to the muscularis mucosae- Muscularis: 2 layers of smooth muscles, inner layer is circular and outer layer is longitudinal, contraction shortens distance- Myenteric plexus is the nerve supply to the muscularis mucosae- Serosa: covering connective tissue- Outer covering of the entire GI tract, replaced by the fibrous adventitia in the oral cavity, pharynx, esophagus, and rectum3. GI Smooth Muscle Contraction (it is spontaneous)- Contraction frequency is set by Basic Electrical Rhythm (BER)- Set by pacemaker cells (interstitial cells of Canal)- Tonic Contractions are in the sphincter and anterior portion of the stomach- Phasic contractions are in the posterior portion of stomach and small intestine- Patterns: Peristalsis- contraction plus distal relaxation, seen mostly in esophagus, stomach, and intestinal. Segmentation- seen predominantly in small and large intestine- Between meals- the migrating motor complex moves all the residual food in the small intestine, housekeeping effect of motility. 4. Modulating Smooth Muscle Contractility- Activating phosphatase would relax smooth muscle- cAMP acts as an inhibitory for MLCK- Antagonists of Gs activates smooth muscle and agonists of Gi as well5. Digestive Enzyme Secretion- Exocrine glands (salivary glands-amylase and some lipase, the pancreas-protease, lipase, and amylase, important for digestion in small intestine) or epithelial cells in the stomach and small intestine can also secrete enzymes. *some are secreted by zymogens (mechanisms to help protect against auto digestion, go into lumen and are activated by other chemicals)6. Mucus Secretion- Very important in protecting the GI tract- Exocrine cells secrete mucus (mucous cells, salivary glands and goblet cells in the small intestine)- Primary function are to protect GI mucosa and lubricate contents- Mucus is stimulated by parasympathetic, cytokines, and neuropeptides7. Digestion and Absorption- Digestion is the process of breaking macromolecules into absorbable units- Absorption takes place in the small intestine , water and ions are in the large intestine- Proteins become amino acids and carbohydrates are broken down into monosaccharides - Products of carbs and proteins are absorbed into the hepatic portal system (the Liver)- Products of fat digestion (chylomicrons) enter lacteal (bypasses liver)8. Enteric Nervous System (ENS) – acts independently- Intrinsic neurons- Responds to many neurotransmitters- Excitatory motility is stimulated by Ach (Gi coupled) or Substance P (Gq coupled)- Inhibitory (smooth muscle relaxation) motility is stimulated by NO(nitric oxide), VIP, & secret motor Ach and VIP- Contains glial cells, diffusion barrier, and integrating center just like the CNS9. Short Reflex - Originate within the ENS and integrated in the ENS- Do not involved anything out the ENS- Cells in the lumen and tell the secretion or motility of enabling cells is an example10. Long Reflex- Must involve neurons from outside the ENS- Can originate in the CNS- Cephalic reflexes such as seeing people that are drinking water, or seeing food.11. GI Peptides- Hormones, neuropeptides, and cytokines- Secreted by isolated endocrine cells in mucosa- Have function not limited to the GI- The primary releasing sight of Gastrin is in the stomach, stimulates gastric acid secretion and mucosal growth, somatostatin inhibits release.- CCK is primarily released in the gallbladder, pancreas, and stomach. It inhibits gastric empting and acid secretion. Also stimulates gallbladder contraction and pancreatic enzyme secretion.12. Saliva- Primarily controlled by autonomic nervous system- Saliva softens and lubricates food- Salivary amylase and some lipase begins chemical digestion- Allows you to taste food and protects you by containing