Digestive System. Lecture Overview (Lectures 7 & 8) Martini s Visual Anatomy and Physiology First Edition

Transcription

1 Martini s Visual Anatomy and Physiology First Edition Martini Ober Chapter 21 - Digestive System I, II Lectures 7 & 8 1 Lecture Overview (Lectures 7 & 8) Introduction to the digestive system General characteristics of the alimentary canal The mouth and tongue Salivary glands Pharynx and esophagus Stomach Pancreas 2 Functions of Digestive System ingestion Digestive System mechanical digestion chemical digestion propulsion Digestion is the mechanical and chemical breakdown of food into a form that cells can absorb absorption excretion defecation 3 1

2 Major Organs of Digestive System Figure from: Saladin, Anatomy & Physiology, McGraw Hill, 2007 Organs can be divided into the: -Digestive tract (primary) (alimentary canal); tube extending from mouth to anus (about 30 ft.) -Accessory organs; teeth, tongue, salivary glands, liver, gallbladder, and pancreas 4 The Greater and Lesser Omenta Figure from: Saladin, Anatomy & Physiology, McGraw Hill, The Mesentery Figure from: Saladin, Anatomy & Physiology, McGraw Hill,

3 The Abdominal Cavity & Peritoneum Notice that the pancreas, duodenum, and rectum are retroperitoneal Figure from: Martini, Anatomy & Physiology, Prentice Hall, Alimentary Canal Continuous tube modified along its length to carry out specialized, regional functions. Mouth, pharynx, esophagus, and anal canal are lined by nonkeratinized stratified squamous epithelium Stomach and intestines are lined by simple columnar epithelium. Why? 8 Alimentary Canal Wall Know the 4 layers of the alimentary canal Figure from: Martini, Anatomy & Physiology, Prentice Hall,

4 Alimentary Canal Wall 10 Movements Through the Alimentary Canal mixing movements (segmentation) peristalsis - The wavelike muscular contractions of the alimentary canal or other tubular structures by which contents are forced onward toward the opening. (Triggered by pacesetter cells.) 11 Innervation of the Alimentary Canal The alimentary canal has extensive sympathetic and parasympathetic innervation - mainly in the muscularis externa - regulates its tone and the strength, rate, and velocity of muscular contractions submucosal plexus controls secretions/blood flow myenteric plexus controls gastrointestinal motility/sphincters parasympathetic division of ANS increases activities of digestive system and relaxes sphincters sympathetic division of ANS generally inhibits digestive actions and contracts sphincters 12 4

5 Mouth (Oral or Buccal cavity) (Labium) ingestion mechanical digestion prepares food for further chemical digestion (Labium) Figure from: Saladin, Anatomy & Physiology, McGraw Hill, Tongue Very muscular; muscles run in several directions Covered by mucous membranes Blast from the past - Root of tongue is anchored to the hyoid bone 1. Tastebuds 2. Friction for food handling 3. Secretes lingual lipase 14 Palate roof of oral cavity (adenoids) Important in separating the nasopharynx from the pharynx during swallowing 15 5

6 Secondary (Permanent) Teeth Total of 32 secondary (permanent) teeth Watch for incoming ICBMs!!! Know the order of these 16 Primary (Deciduous, Baby, Milk) Teeth (Mastication = chewing) 8 incisors 4 cuspids 8 molars 20 total All primary teeth are lost, generally between ages 6 and Section of a Tooth Oh no! Not again! What type of articulation is this? Know this diagram for exam 18 6

7 Moistens food Binds food particles Functions of Saliva Dissolves food for tasting Begins chemical digestion of complex CHO (amylase) Cleans teeth and mouth (ph = ) Anti-microbial (IgA and lysozyme) 19 Salivary Glands 20 Secretions of Salivary Glands Secretions are slightly acidic and continual due to basal parasympathetic stimulation, but increase after - presence, or anticipation of, food; - parasympathetic stimulation (watery, large volume) - sympathetic stimulation (viscous, small volume) Parotid glands clear primarily water, serous fluid rich in amylase mumps virus typically attacks here Submandibular glands primarily serous fluid some mucus, amylase Sublingual glands primarily mucus most viscous 21 7

8 Pharynx Pharynx aids swallowing by grasping food and moving it toward the esophagus. 22 Three Phases of the Swallowing Reflex Only voluntary phase is the buccal (oral) phase, i.e., the initiation of swallowing, then soft palate and uvula raise hyoid bone and larynx elevate epiglottis closes off top of trachea longitudinal muscles of pharynx contract inferior constrictor muscles relax and esophagus opens peristaltic waves push food through pharynx Pharyngeal phase reflexive Esophageal phase 23 Swallowing Mechanism 24 8

9 Esophagus Veins drain into hepatic portal vein (via gastric veins) Lower esophageal (cardiac) sphincter prevents reflux (backup) of stomach acid into the esophagus. Esophagus conveys food from pharynx to stomach by peristalsis 25 Stomach M Gastric glands Stomach can hold about liters of material Rugae flatten as stomach fills M G cells D cells Greater curvature Stomach Functions: - Mixing - Reservoir - Secretion of gastric juice - Digestion, anti-bacterial action, facilitates absorption of vitamin B 12 - Secretion of gastrin, somatostatin 26 Blood Supply and Drainage of Stomach Figure from: Martini, Anatomy & Physiology, Prentice Hall,

10 Lining and Gastric Glands of Stomach Figure from: Martini, Anatomy & Physiology, Prentice Hall, mucus (cardia) from goblet cells and mucous glands protective to stomach wall pepsinogen from chief cells inactive form of pepsin pepsin from pepsinogen in presence of HCl protein splitting enzyme Gastric Secretions INFANTS ONLY rennin (chymosin) gastric lipase hydrochloric acid from parietal cells needed to convert pepsinogen to pepsin p in parietal and p in ph intrinsic factor from parietal cells required for vitamin B 12 absorption mucus, gastrin, somatostatin from pyloric glands protective to stomach wall gastrin and somatostatin are hormones 29 Secretion of H by Parietal Cells Important functions of the stomach ph ( ) - kills microorganisms - denatures proteins - breaks down plant material and CT in meats - activates pepsin Figure from: Martini, Anatomy & Physiology, Prentice Hall,

11 Three Phases of Stomach Control Cephalic phase triggered by smell, taste, sight, or thought of food begin secretion and digestion Gastric phase triggered by distension, presence of food, and rise in ph in stomach enhances secretion and digestion Intestinal phase triggered by distension of small intestine and ph change controls rate of gastric emptying; may slow emptying NOTE that all these phases control activity in the STOMACH Know what each phase does (shown in red) 31 Cephalic Phase of Gastric Secretion Emotional states can exaggerate or inhibit this phase Figure from: Martini, Anatomy & Physiology, Prentice Hall, Gastric Phase of Gastric Secretion Proteins, alcohol, and caffeine can markedly increase secretions by stimulating gastric chemoreceptors Histamine stimulates acid secretion by parietal cells Figure from: Martini, Anatomy & Physiology, Prentice Hall,

12 Intestinal Phase of Gastric Secretion Enterogastric reflex (inhibits gastric activity) reduces gastric motility, stimulates contraction of pyloric sphincter (pylorus) Figure from: Martini, Anatomy & Physiology, Prentice Hall, Overview of Gastric Control/Secretion Key Stimulation ph < 3.0 Emptying of Stomach ( [H ]) (intestinal phase) Fats in Small Intestine D cells Somatostatin Stomach Molility (Segmentation/Peristalsis) ph > 3.0 (dilution of H ) - Food in Stomach (cephalic/gastric phases) Parasympathetic NS G cells Gastrin Stretch of stomach Both Mucous Cells Peptides Protein Breakdown Fat Breakdown ECL Cells Histamine Parietal Cells Chief Cells Lipases - Inhibition Endocrine Factor Exocrine Factor Intrinsic Factor HCO 3- (alkaline tide) Pepsinogen H Cl - Pepsin B Mixing and Emptying Actions 36 12

13 Gastric Absorption Gastric absorption is very limited due to: - blanket of mucus covering cells - epithelial cells lack specialized transport mechanisms - tight junctions between adjacent epithelial cells - gastric lining is relatively impermeable to water - chyme usually contains only partially digested material Some substances can be absorbed by the stomach: some water certain salts certain lipid-soluble drugs, e.g., aspirin alcohol (slowed by presence of fats) 37 Pancreas Exocrine (digestive) and endocrine (metabolic) functions Completes digestion of proteins that was started in the stomach 38 Blood Supply and Drainage of Pancreas Figure from: Martini, Anatomy & Physiology, Prentice Hall,

14 Pancreatic Juice pancreatic amylase splits glycogen into disaccharides pancreatic lipases break down triglycerides pancreatic nucleases digest nucleic acids bicarbonate ions make pancreatic juice alkaline (ph = 8) and neutralize acid coming from stomach Pancreatic proteolytic enzymes 40 Pancreatic Proteolytic Enzymes Enteropeptidase (Enterokinase) (brush border of sm. intestine) Know this chart Trypsinogen Trypsin Pancreas Chymotrypsinogen yp Procarboxypeptidase Proelastase (Proenzymes, Zymogens) Chymotrypsin yp Carboxypeptidase Elastase (Active enzymes) Dipeptides, tripeptides, amino acids Proteins Purpose of proteolytic enzymes is continued breakdown of proteins that began in the stomach 41 Regulation of Pancreatic Secretions acidic chyme stimulates release of secretin secretin stimulates release of watery pancreatic juice with bicarbonate and phosphate (= buffers; to ph) CCK and parasympathetic NS stimulate production and secretion of pancreatic enzymes and zymogens 42 14

15 Secretin Bile and Pancreatic ducts Regulation of Pancreas/Intestinal Digestion HCO 3-, PO 4 3- ph to 8 (req. for enzyme action) Lacteals Gallbladder Contraction Bile Triglycerides Cholesterol Fat Soluble Vitamins Acidic Chyme Enters Duodenum Cholecystokinin (CCK) Relaxation of hepatopancreatic sphincter Lipases (emulsification) Fatty acids, monoglycerides (brush border) Enterokinase Trypsinogen Trypsin Pancreas Chymotrypsinogen Trypsinogen Procarboxypeptidase Proelastase Carboxypeptidase Elastase Nucleases (DNA, RNA) Nucleotides Portal Vein (proenzymes, zymogens) Amylase (glycogen, starches) Proteins Mono-, di-, trisaccharides Action of brush border enzymes Key Di- and tripeptides Stimulation Subclavian vein Conversion to chylomicrons Monosaccharides Amino acids 43 Alimentary canal (direct contact with food) Mouth, pharynx, esophagus, stomach, small and large intestines, anal canal Accessory structures (no direct contact with food, but provide secretions) Sli Salivary glands, liver, gall llbldd bladder, pancreas Four layers of the alimentary canal Mucosa absorption, secretion, protection Submucosa nutrition and transport Muscularis movement Serosa protection, lubrication 44 Wave-like movement of alimentary canal is called peristalsis Results from stretching Bowel sounds Innervation of the alimentary canal (enteric nervous system) Parasympathetic increases activity Sympathetic decreases activity Mouth Mastication mechanical processing of food and mixing with saliva 45 15

16 Tongue Lined by mucous membranes Thick, skeletal muscle Papillae function in food handling and taste Lingual frenulum Lingual tonsils Lingual glands secrete lingual lipase Palate (roof of oral cavity) Hard palate (Palatine proc. of maxillary bones) Soft palate Uvula is suspended from this Uvula closes opening to nasal cavity (nasopharynx) 46 Tonsils Lingual (back of tongue) Palatine (lateral to tongue) Pharyngeal (posterior wall of pharynx; adenoids) Teeth Teeth Primary teeth (deciduous teeth; baby teeth) 6 months to 2-4 years 20 total Secondary (permanent teeth) 6 yrs to years 32 total 47 Teeth (continued) Incisors sharp for biting Cuspids (canine) for grasping/tearing Bicuspids and molars grinding Structure Crown above gum line Root below gum line Outer covering is enamel hardest substance in body NOT replaceable Inner substance is dentin (alive) Pulp cavity Periodontal ligament 48 16

17 Alimentary canal (direct contact with food) Mouth, pharynx, esophagus, stomach, small and large intestines, anal canal Accessory structures (no direct contact with food) Sli Salivary glands, liver, gall llbldd bladder, pancreas Four layers of the alimentary canal Mucosa absorption, secretion, protection Submucosa nutrition and transport Muscularis movement Serosa protection, lubrication 49 Wave-like movement of alimentary canal is called peristalsis Results from stretching Bowel sounds Innervation of the alimentary canal (enteric nervous system) Parasympathetic increases activity Sympathetic decreases activity Mouth Mastication mechanical processing of food and mixing with saliva 50 Tongue Lined by mucous membranes Thick, skeletal muscle Papillae function in food handling and taste Lingual frenulum Lingual tonsils Lingual glands secrete lingual lipase Palate (roof of oral cavity) Hard palate (Palatine proc. of maxillary bones) Soft palate Uvula is suspended from this Uvula closes opening to nasal cavity (nasopharynx) 51 17

18 Tonsils Lingual (back of tongue) Palatine (lateral to tongue) Pharyngeal (posterior wall of pharynx; adenoids) Teeth Primary teeth (deciduous teeth; baby teeth) 6 months to 2-4 years 20 total Secondary (permanent teeth) 6 yrs to years 32 total 52 Teeth (continued) Incisors sharp for biting Cuspids (canine) for grasping/tearing Bicuspids and molars grinding Structure Crown above gum line Root below gum line Outer covering is enamel hardest substance in body NOT replaceable Inner substance is dentin (alive) Pulp cavity Periodontal ligament 53 Salivary glands produce saliva which Moistens food Binds food particles Begins chemical digestion of CHO Dissolves food (for taste) Cleanses mouth and teeth; antibacterial i Three pairs of salivary glands Parotid; front of ear, watery fluid rich in amylase Submandibular; floor of mouth, viscous fluid Sublingual; below tongue, thick, stringy secretion 54 18

19 Salivary glands Sympathetic stimulation small quantity of viscous saliva Parasympathetic stimulation large volume of watery saliva Pharynx Cavity connecting mouth with esophagus Nasopharynx, oropharynx, laryngopharynx Muscles Inner circular constriction Outer longitudinal movement of food bolus 55 Swallowing Initiation is voluntary; act of swallowing is NOT it s a reflex Three stages Chewing and rolling of food into oropharynx (voluntary, buccal) Swallowing reflex (pharyngeal) Epiglottis closes over larynx Muscles in lower pharynx relax Esophagus opens and food moves in Peristalsis in esophagus transports food to stomach (esophageal) Esophagus Muscular tube connects to cardiac region of stomach Esophageal hiatus Lower esophageal (cardiac) sphincter 56 Stomach Cardiac, fundus, body, pylorus Mixes food and begins digestion of protein Limited absorption (alcohol) Moves food into small intestine Pyloric sphincter (entrance to small intestine) Rugae and gastric pits Gastric glands Mucous cells (goblet) secrete mucous Chief cells (peptic) secrete digestive enzymes, esp. pepsinogen Parietal cells (oxyntic) secrete HCl (Parietal, ph) Infants only - Gastric lipase and rennin 57 19

20 Regulation of gastric activity Cephalic phase (primarily neural) Prior to food entry into stomach Increased motility and production of gastric juice Gastric phase Neural: Food entering stomach / ph rising Hormonal: gastrin release Local: histamine release (stimulates parietal cells) Intestinal phase Neural: distension of duodenum (enterogastric reflex) Hormonal: CCK, GIP, and secretin, gastrin Reduction (slowing) of gastric emptying 58 Pancreas Both exocrine and endocrine functions Main source of intestinal digestive enzymes Pancreatic amylase (starches) Pancreatic lipase (fats) Nucleases Proteolytic proenzymes / enzymes Regulation of pancreatic activity Acid chyme stimulates secretin Secretin stimulates watery buffering secretion Parasympathetic NS and CCK stimulate production and secretion of digestive enzymes 59 20