Digestive System – Part 2 PDF

Digestive System – Part 2 © 2015 Pearson Education, Inc.  Oral Cavity/Mouth Hard palate Soft palate Hard and soft palate...

Digestive System – Part 2 © 2015 Pearson Education, Inc.  Oral Cavity/Mouth Hard palate Soft palate Hard and soft palate Oral Cavity Teeth Uvula Tongue Salivary Glands Palatine tonsil Tongue Mechanical breakdown Some chemical breakdown No absorption An anterior view of the oral cavity as seen through the open mouth © 2015 Pearson Education, Inc.  Mechanical Digestion Oral cavity: lips, cheeks, and palate help guide and contain the food Mechanical digestion by teeth = Mastication Sublingual gland Saliva: produced by salivary glands and Parotid Submandibular released into the mouth: gland gland 99.5% water, electrolytes, mucus Salivary Amylase: enzyme for carbohydrate digestion Lysozyme: antibacterial enzyme Also helps with motility, taste, cleansing the mouth, and speaking © 2015 Pearson Education, Inc.  Incisors Tongue Skeletal muscle Canine Mechanical breakdown: mixes food with saliva and compacts it Premolars into a bolus Molars Tooth #16 Teeth #1 Two sets of teeth in a life time: Tooth #17 - 20 deciduous teeth - baby or #32 “milk” or primary teeth - 32 succedaneous teeth - permanent teeth © 2015 Pearson Education, Inc.  Pharynx Pharynx (throat) - shared passageway for air and food Food moves from the mouth through the oropharynx and Pharynx laryngopharynx to the esophagus Esophagus Esophagus Muscular tube from pharynx to stomach Upper 1/3 – skeletal muscle, middle 1/3 - mixed, lower 1/3 - smooth muscle Posterior to the trachea, travels through diaphragm before entering stomach Both involved in swallowing © 2015 Pearson Education, Inc.  Swallowing (deglutition) – total time ~9 seconds! Can be initiated voluntarily, but proceeds automatically Buccal Phase Soft palate Skeletal Muscles Bolus Epiglottis Voluntary Esophagus Trachea 1. Compression of bolus against hard palate. 2. Elevation of soft palate, sealing off nasopharynx 3. Tactile receptors at uvula - reflex responses begin 4. Bolus is moved toward stomach © 2015 Pearson Education, Inc.  Pharyngeal Phase Tongue Bolus 1. Bolus comes into contact with pharyngeal wall 2. Elevation of larynx and folding of epiglottis – windpipe closed! © 2015 Pearson Education, Inc.  Esophageal Phase Peristalsis Trachea Peristaltic contraction of pharyngeal muscles force bolus into esophagus, peristalsis also moves bolus toward stomach. © 2015 Pearson Education, Inc.  Bolus Enters Stomach Thoracic cavity Lower esophageal sphincter Stomach 1. Bolus triggers opening of lower esophageal sphincter. 2. Bolus continues into the stomach. © 2015 Pearson Education, Inc.  Esophageal Sphincters The esophagus is closed off at its upper and lower ends by sphincters Pharyngoesophageal sphincter: between pharynx and esophagus, preventing air from gastroesophageal entering when food is not being swallowed sphincter Gastroesophageal sphincter: between esophagus and stomach, controls the entry of food and prevents stomach acid backflow Stomach Functions Storage of large contents of partially digested food, called chyme (expansion from 50ml (empty) to 1000ml (full)) Movement: peristalsis Secretions: “gastric juices” Digestion: mostly proteins, carbohydrates (a little) (Absorption: Alcohol and Aspirin) © 2015 Pearson Education, Inc.  Lesser curvature – medial concave surface Greater curvature – lateral convex surface Anatomy of the Cardia – first part near the gastroesophageal sphincter Stomach Fundus – expanded lateral portion Gastroesophageal junction Body – midportion Fundus Longitudinal muscle layer Cardia Circular muscle layer Oblique muscle layer Body Lesser curvature Pyloris Pyloric sphincter Rugae Greater curvature (lateral surface) Pyloric region – funnel shaped, continuous with the small intestines through © 2015 Pearsonthe pyloric Education, Inc. sphincter Peristalsis The stomach mechanically breaks down food and moves it to the small intestines through peristalsis = waves of smooth muscle contractions Gastric mixing and gastric emptying Motility regulation of the stomach: Motility Volume: when full, motility and emptying is stimulated Gastric Fluidity: when material is broken emptying down = pulpy, mushy chyme = emptying will be stimulated Motility High levels of fat, acid, and distension of small intestine will inhibit emptying until the small Peristaltic intestine can process more Contraction Stress: inhibits motility and emptying (Gastric mixing) via SNS © 2015 Pearson Education, Inc. Gastric Juices: Gastric Pits & Gastric Glands Gastric pits are extensions of the epithelium into the lamina propria Gastric glands contain 4 types of cells make gastric juices Gastric pit Gastric gland © 2015 Pearson Education, Inc. Stomach Cells (in Gastric pits) Exocrine cells: Mucous cells – thin, watery mucus to protect stomach wall from harsh acids Chief cells – pepsinogen, precursor to pepsin, an enzyme that digests proteins Parietal cells – Hydrochloric acid (HCl) (and Intrinsic factor needed for vitamin B12 absorption) Endocrine cells: G cells – produce hormone gastrin which stimulates gastric juice production and smooth muscle contraction ECL cells: produce/release histamine - increases HCl D cells: Somatostatin release inhibits HCl, gastrin and histamine release when acid is high © 2015 Pearson Education, Inc.  Autocatalysis Stomach: HCl Functions Digestion Pepsinogen Pepsin HCl in the gastric juice has 4 Protein main functions: Gastric lumen HCI 1) Activates pepsin for protein Peptide fragments digestion Pepsinogen → pepsin 2) Breaks down tough fibrous foods 3) Denatures proteins 4) Kills bacteria and other microorganisms =Various amino acids © 2015 Pearson Education, Inc. Enzymatic splitting of a chemical bond © 2015 Pearson Education, Inc.  Regulation of gastric activity – motility and secretions Controlled by the CNS Regulated by short reflexes of ENS & regulated by hormones of digestive tract Three phases of gastric control 1. Cephalic phase (get ready for food…) 2. Gastric phase (deal with food…) 3. Intestinal phase (allow time for proper digestion…) © 2015 Pearson Education, Inc. Cephalic phase Prepares the stomach to receive food Short (2-10min) Gastric juice Food Sight, smell, taste, production ~500ml/h or thoughts of food CNS Vagus nerve (N X) Summary: Submucosal Sensations related to food plexus lead to parasympathetic signaling to submucosal Mucous Mucus plexus cells Submucosal plexus signals Chief Pepsinogen cells to secretory cells Gastrin Parietal HCl Secretory cells release cells mucus, enzymes, and acid G cells KEY Stimulation Stimulation © 2015 Pearson Education, Inc. Gastric phase Builds on stimulation from cephalic phase 2-4 hours Mixing and Neural Response secretions Summary: Arrival of food leads to stomach Submucosal and Distension Stretch myenteric plexuses receptors stretch and elevated pH Elevated pH Chemoreceptors Receptors signal to Mucous cells Mucus submucosal and via bloodstream Chief myenteric plexuses cells PepsinogenMixing Submucosal and Parietal waves Gastrin HCl myenteric plexuses cells signal to secretory G cells Partly cells and smooth digested muscle peptides Secretions and via bloodstream peristalsis © 2015 Pearson Education, Inc. Intestinal phase Summary: Food moves into Controls the rate of gastric emptying duodenum Duodenum stretch and pH Neural Responses change leads to inhibition of peristalsis Hormones Myenteric Enterogastric released from plexus duodenum inhibit reflex secretory cells via bloodstream Chief cells Activates Parietal pancreas and Duodenal cells stretch and Peristalsis gallbladder chemoreceptors Insulin Presence of CCK secretion lipids and GIP carbohydrates KEY Activates pancreas to Secretin Decreased pH Inhibition release HCO3- © 2015 Pearson Education, Inc. Reflexes due to filling stomach Gastroenteric reflex: Stomach distension motility and secretion along entire small intestine increases. Gastroenteric reflex Gastroileal reflex Gastroileal reflex: Presence of food in stomach and gastric peristalsis opening of ileocecal valve food moves on to large intestines © 2015 Pearson Education, Inc. Small Intestine Anatomy From stomach to large intestine Folded surface for increased surface area for absorption Plicae circulares – circular ridges in the mucosa and submucosa Villi – finger-like projections of the mucosa, contains capillaries and lacteals Microvilli – tiny projections of the epithelial cells Plica circulares Small Villi Intestine Microvilli © 2015 Pearson Education, Inc. Three Regions of Small Intestine Duodenum Duodenum – first part (10 inches) Chemical digestion: majority in the Jejunum body occurs here, enzymes received from pancreas, bile salts from the liver Brunner’s glands: alkaline mucous secreting glands to neutralize acid entering from stomach Jejunum – middle part (8 feet) nutrient absorption: majority occurs here Ileum – last part (12 feet) ends at ileocecal valve major site of Vitamin B12 absorption Ileum return of bile salts to the liver via enterohepatic circulation Peyer’s Patches: MALT (mucosa associated lymphatic tissue) in the submucosa © 2015 Pearson Education, Inc.  Jejunum Serosa Duodenum Muscularis externa Duodenal Submucosa (Brunner’s) glands Mucosa Muscularis Villi mucosae Peyer’s patches Ileum © 2015 Pearson Education, Inc.  Small Intestine: Movement by Segmentation Segmentation is a series of ring-like contractions using circular muscle that mixes and propels chyme in the small intestine 9-12 cycles per minute 3-5 hours to move food completely through © 2015 Pearson Education, Inc.  Small Intestine: Secretions Microvilli (brush Mucus border) Brush Border enzymes: Enterokinase: activates trypsin (protein digestion) Disaccharidases: breaks down Epithelial disaccharides into monosaccharides cell Aminopeptidases: breaks down peptides into amino acids Enterogastrones: group of hormones released from the small intestine to inhibit stomach secretions and motility Cholecystokinin (CCK): also activates pancreas and gallbladder Secretin: also activates pancreas to release bicarbonate (HCO3-) Gastric inhibitory polypeptide (GIP): also stimulates insulin secretion © 2015 Pearson Education, Inc.  Small Intestine: Absorption Passive Diffusion: Fatty acids and triglycerides (after micelles deliver them to epithelial surface) Vitamins Active Transport: H+ and Na+ actively transported by sodium-hydrogen antiporter Gradients used to transport small molecules across the epithelium via symporters (secondary active transport): glucose, amino acids, electrolytes Water follows Na+ © 2015 Pearson Education, Inc.