Hunger and satiety_ Video, Anatomy & Definition _ Osmosis

NOTES ENTERIC NERVOUS SYSTEM ~ osms.it/enteric-nervous-system-and-slow-waves = [ntrinsic component of gastrointestinal PARASYMPATHETIC INNERVATION (Gl) innervation that can function without = Parasympathetic ganglia located within extrinsic innervation myenteric, submucosal plexuses = Communicates with sympathetic nervous » Parasympathetic preganglionic, system, parasympathetics postganglionic neurons either cholinergic = Ganglia located in myenteric, submucosal (release acetylcholine) or peptidergic plexuses (release substance P/vasoactive intestinal = Myenteric/Auerbach’s plexus: located peptide) between longitudinal, circular smooth = Vagus nerve innervates upper Gl muscle layers; Gl movement function = Upper ¥ of esophagus, stomach, small = Submucosal/Meissner’s plexus: located intestine, ascending, proximal transverse in submucosa; function in Gl secretions, colon blood flow = Consists of 75% afferent, 25% efferent = Neurons of extrinsic system release fibers neurocrines = Vagovagal reflexes: reflexes in which = Neurochemicals consisting of both afferent, efferent limbs originate neurotransmitters, neuromodulators from vagus nerve = Extrinsic branch of Gl innervation = Sympathetic, parasympathetic divisions MUCOSA f ' SUBMUCOSAL/MEISSNER'S PLEXVUS SUBMUCOSA{ CIRCULAR SMOOTH MUSCLE MYENTERIC/AVERBACH'S PLEXVUS MUSCULARIS PROPRIA apventTimas | | ' | SEROSA () AR Lifi Figure 371 Locations of the myenteric (Auerbach’s) and submucosal (Meissner’s) plexuses within the four layers of the gastrointestinal tract. The myenteric plexus is located between the circular and longitudinal smooth muscle layers, which produce different movements in the Gl tract. LONGITUDINAL SMOOTH MUSCLE 302 OSMOSIS.ORG

= Pelvic nerves innervate lower Gl = Distal transverse colon, descending, sigmoid colon PARASYMPATHETIC INNERVATION o \ VAGUS NERVE PELVIC | NERVES SPINAL CORD Figure 37.2 The vagus nerve provides parasympathetic innervation from the upper esophagus to the proximal transverse colon. The pelvic nerve provides innervation from the distal transverse colon to the rectum. SYMPATHETIC INNERVATION = Sympathetic preganglionic neurons synapse in ganglia outside Gl tract = Celiac, superior mesenteric, inferior mesenteric, hypogastric ganglia = Sympathetic postganglionic neurons either synapse on ganglia in myenteric/ submucosal plexuses or directly innervate target organs = Sympathetic preganglionic neurons are cholinergic; sympathetic postganglionic neurons are adrenergic (release norepinephrine) MECHANISMS = Slow waves = Duodenum: 12 waves/minute = [leum: 9 waves/minute = Migrating myoelectric complexes every 90 minutes clears any remaining chyme SYMPATHETIC INNERVATION | 1. CELIAC GANGLION . SUPERIOR MESENTERIC GANGLION 3. INFERIOR MESENTERIC GANGLION 4. HYPOGASTRIC GANGLION Figure 37.3 Sympathetic preganglionic neurons synapse outside the Gl tract, in the four ganglia shown above. = Sympathetic via fibers from celiac/superior mesenteric ganglia — | contractions = Two forms of contractions; coordinated by enteric nervous system Innervation = Parasympathetic via vagus nerve (CN X) = 1 contractions; most nerves cholinergic, some release neurocrines (e.g. peptidergic) = Motilin = Secreted by endocrinocytes in proximal small intestine, regulate contractions = Vasoactive intestinal peptide (VIP) = [Induces smooth muscle relaxation (e.g. sphincters); induces water secretion into pancreatic juice, bile; inhibits gastric acid secretion = Enkephalins = Inhibitory modulators in myenteric, submucosal plexuses Segmental contractions (| diameter) = Mix, expose chyme to secretions, enzymes = Contraction — splits chyme — both orad, caudad directions — relaxation — merging of chyme — repeated Chapter 37 Gastrointestinal Physiology: Gastrointestinal Function OSMOSIS.ORG 303

GASTROINTESTINAL HORMONES osms.it/gastrointestinal-hormones Chapter 37 Gastrointestinal Physiology: Gastrointestinal Function SOMATOSTATIN = Members of G protein coupled-receptor superfamily Function = | secretion of many other hormones (e.g. gastrin, bicarbonate, digestive enzymes) = | nutrient absorption from gut by prolonging gastric emptying time = | pancreatic secretions = | visceral blood flow Secretion and activation = Central nervous system, pancreatic delta cells, enteroendocrine delta cells = Somatostatin binds receptors — activates inhibitory G protein — inactivate adenylate cyclase — | cAMP production — protein kinase not activated — | Ca?* — inhibitory effect = Site of action = Stomach, pancreas, small intestine, gallbladder, liver = Secretory stimulants = Glucose, argining, leucine, glucagon, vasoactive intestinal peptide (VIP), cholecystokinin (CCK) GASTRIN Function = Induces gastric acid secretion Secretion and stimulation/inhibition = Secreted by enteroendocrine G cells of stomach, duodenum = Secretory stimulants = Presence of acidic content, partially digested food in duodenum, vagus nerve stimulation = Inhibited by somatostatin MOTILIN Function = Stimulates gastric, pancreatic enzyme secretion Secretion and stimulation/inhibition = Secreted by enteroendocrine M cells of proximal small intestine = Secretory stimulants = Duodenal alkalinization, gastric distension = Inhibited by duodenal nutrients PANCREATIC PEPTIDE (PP) Function = | gastric emptying, slows small intestine motility Secretion and stimulation/inhibition = Secreted by endocrine cells in pancreatic islets = Secretory stimulants: intraluminal nutrients, vagal nerve activation, hypoglycemia PEPTIDE Y (PPY) Function = Inhibits gastric acid secretion, gastric motility, slows intestinal motility = Inhibits pancreatic exocrine secretion Secretion and stimulation/inhibition = Secreted by pancreatic islet alpha cells, enteroendocrine cells = Secretory stimulants = [ngestion of nutrition, bile acids, fatty acids OSMOSIS.ORG 305

306 OSMOSIS.ORG SECRETIN Function = | acidity to improve pancreatic enzyme function = 1 pancreatic secretion, biliary bicarbonate, water = Regulates pancreatic enzyme secretion = | gastric emptying, gastrin release, gastric acid secretion Secretion and stimulation/inhibition = Secreted by enteroendocrine S cells in proximal small intestine = Secretory stimulants = Gastric acid, bile salts, peptides, fatty acids, ethanol = Inhibited by somatostatin CHOLECYSTOKININ (CCK) Function = Promotes food delivery from stomach into small intestine = Regulates nutrient-stimulated enzyme secretion = 1 gallbladder contraction = 1 enzymatic pancreatic secretion output Secretion and stimulation/inhibition = Secreted by enteroendocrine | cells = Secretory stimulants = Nutrition ingestion, fatty acids, amino acids INSULIN Function = Major anabolic hormone = | blood glucose = Promotes liver, muscle glycogen storage = Fatty acids, triacylglycerol storage in adipose tissue = Protein synthesis, glucagon suppression Secretion and stimulation/inhibition = Secreted by beta cells of pancreatic islet cells = Secretory stimulants = High blood glucose, glucose, arginine, leucine, glucagon, VIP, CCK = Inhibited by somatostatin GLUCAGON Function » Counteracts insulin = 1 blood glucose, promotes glycogenolysis, gluconeogenesis, ketogenesis = Works mainly on liver Secretion and stimulation/inhibition = Secreted by alpha cells of islet cells, L-cells of intestine = Inhibited by somatostatin INCRETINS = Includes glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic peptide (GIP) Function = 1 insulin release from pancreatic beta-cells = 1 levels of cCAMP in islets leading to expansion of beta-cells GASTRIC INHIBITORY PEPTIDE (GIP) = AKA glucose-dependent insulinotropic peptide Function = Weakly inhibits HCI production, stimulates insulin release Secretion and stimulation/inhibition = Secreted by duodenal mucosa = Secretory stimulant = Fatty chyme HISTAMINE Function = Activates parietal cells to release HCI Secretion and stimulation/inhibition = Secreted by stomach mucosa = Secretory stimulant = Food in stomach

308 SATIETY osms.it/satiety = Hypothalamus controls appetite, satiety = Ventral posteromedial nucleus (VPN) of hypothalamus: activates satiety o Lateral hypothalamic area: activates hunger, feeding HORMONES Leptin = Stimulates satiety, decreases appetite = Secreted by fat cells in proportion to fat amount in adipocytes Ghrelin = Increases appetite, hunger = Secreted by gastric cells before meal Insulin = Stimulates satiety, decreases appetite = Fluctuates throughout day Peptide YY (PYY) = Stimulates satiety, decreases appetite directly (via hypothalamus), indirectly (via inhibiting release of ghrelin) GLP-1 = Stimulates satiety, decreases appetite = Secreted by intestinal L cells = Starvation, weight loss stimulates ghrelin release / HYPOTHALAMUS <t | (CORONAL SECTION) N Y LATERAL HYPOTHALAMIC AREA VENTRAL POSTEROMEDIAL NUCLEUS Figure 37.4 Locations of two areas in the hypothalamus that control appetite and satiety. OSMOSIS.ORG