Gastrointestinal Functions Motility, Nervous Control and Blood Circulation

1. Gastrointestinal FunctionsMotility, Nervous Control and Blood Circulation Prof. Dr. Bayram Yılmaz Yeditepe University Faculty of Medicine Department of Physiology

2. Digestive System www.pennmedicine.org/encyclopedia/em_DisplayAnimation.aspx?gcid=000041&ptid=17

3. THE MAJOR COMPONENTS OF THE HUMAN DIGESTIVE SYSTEM

4. Intestines & Functions

5. Functions of the GI system • Movement of food • Secretion and digestion • Absorption • Circulation of blood and transport of absorbed substances • Control of all these functions by local, nervous and hormonal systems

7. MACROSCOPIC VIEW OF THE WALL OF TUBULAR STRUCTURES OF THE GI • Serosa • Longitudinal muscle layer • Circular muscle layer • Submucosa • Mucosa

8. MACROSCOPIC VIEW OF THE WALL OF TUBULAR STRUCTURES OF THE GI

9. Electrical Activity of GI Smooth Muscle • Slow waves • Electrical pacemakers: interstitial cells of Cajal • Spike potentials • Resting membrane potential (- 50 - 60 mV) • Ca-Na channels and long duration of action potentials

10. Changes in Voltage of Membrane Potentials Factors that depolarize the membrane • Stretching of the muscle • Stimulation by ACh • Stimulation by parasympathetic nerves – ACh • Stimulation by several specific GI hormones Hyperpolarization, sympathetic system, norepinephrine and epinephrine

11. Calcium ions and muscle contraction • Tonic contraction of some GI smooth muscle • GI smooth muscle contractions are tonic and continuous

12. Enteric Nervous System Myenteric (Auerbach’s) plexus Submucosal (Meissner’s) plexus

13. Enteric Nervous System • Stimulation of Myenteric plexus is followed by increased muscle tonus and motility • Some nerve endings of myenteric plexus secrete VIP: its inhibitory effect on sphincters • Signals that stimulate submucosal plexus originate from the GI epithelium • It controls secretions and absorption in the GI tract

14. Types of Neurotransmitters Secreted by Enteric Neurons • ACh • Norepinephrine • Others include • ATP • Serotonin • Dopamine • Cholecyctokinin (CCK) • Substance P • Vasoactive intestinal polypeptide (VIP) • Somatostatin • Enkephalin • Bombesin

15. CONNECTIONS of ENS

16. Anatomy of Autonomic Pathways

17. Parasympathetic Control • Neurotransmitter • Ach • Near the neurons of myenteric and submucosal plexuses • Nerve(s) • Vagus • From esophagus to mid transverse colon • Pelvic nerve • Supplies mid-transverse colon to rectum • ParasympatheticNervousSystem Functions • Increase peristalsis • Stimulates secretions • Relaxes sphincters • Increases gut motility

18. Sympathetic Control • Neurotransmitter • Norepinephrine • Location • Intermediolateral SC (T5-L2) • Superior and inferior mesenteric nerves (T9-T12) • Functions • Decrease peristalsis • Inhibits secretions • Contracts sphincters • Decreases gut motility

19. Autonomic neural pathways • Parasympathetic • Upper via Vagus nerve innervates… • Upper segments of GI tract to splenic flexure • Lower via Pelvic splanchnic nerves • S2-S4 to the descending colon and rectum • Function • Stimulates GI secretion, motor activity • Relaxes sphincters and blood vessels 80 % of the fibers in the Nervus Vagus are afferent

20. Autonomic neural pathways • Sympathetic • T5 - L2 spinal cord segments • Function • Inhibition of GI secretion, motor activity • Contraction of GI sphincters and blood vessels • Somatic • Pudendal nerve • S2-S4 • External anal sphincter and pelvic floor

21. Gastrointestinal Reflexes • 1) Reflexes that are integrated entirely within the gut wall enteric nervous system • 2) Reflexes from the gut to the prevertebral sympathetic ganglia and then back to the GI tract • 3) Reflexes from the gut to the spinal cord or brain stem and then back to the GI tract • Control of gastric motor and secretory functions • Pain reflexes causes general inhibition in the GI tract • Defecation reflexes

22. GI Reflexes (2) • Gastrocolic • Increase in colonic activity after a meal • Distention of the stomach stimulates evacuation of the colon • Enterogastric • Distention and irritation of the small intestine results in suppression of secretion and motor activity in the stomach • Colocolonic • Propels stool caudally by proximal muscle constriction and distal dilatation • Mediated by myenteric plexus • Rectocolic • Colonic peristalsis due to stimulation of rectum • Mediated by pelvic nerve

23. Hormonal Control of GI Motility • Gastrin: secretedby “G” cells of theantrum of thestomach • Cholecystokinin: secretedby I cells in themucosa of duodenumandjejunum • Secretin: producedby S cells in themucosa of duodenum • Bombesin: secretedby P cells in theduodenumandstomach. StimulatesgastrinreleaseandHClsecretion, smoothmusclecontractions. • Gastricinhibitorypeptide (uppersmallintestine) • Motilinincreases GI motility

24. Enteric Endocrine System • Gastrin • Secreted from the stomach • Control of gastric acid secretion • Cholecystokinin • Secreted from the small intestine • Stimulates secretion of pancreatic enzymes and bile. • Secretin • Secreted from the small intestine • Stimulates secretion of a bicarbonate-rich fluids from the pancreas and liver

25. GI Neurotransmitters & Modulators

26. Digestion of Carbohydrates Proteins Fats

27. Types of Movement in the GI tract • Propulsivemovements (peristalsis) • Function of themyentericplexus in peristalsis • Direction of movement of peristalticwaves • Mixingmovements • Theydiffer in differentparts of the GI tract www.pennmedicine.org/encyclopedia/em_DisplayAnimation.aspx?gcid=000097&ptid=17

28. Gastrointestinal Blood Flow Splanchnic Circulation • It includes the blood flow through the gut itself + blood flows through spleen, liver and pancreas Portal vein Liver sinusoids Hepatic veins – vena cava ReticuloEndothelial cells Transport of water soluble nutrients Fats and lymphatic thoracic duct

29. Anatomy of the GI Blood Supply • Along the muscle bundles • Into the intestinal villi • Into the submucosal vessels beneath the epithelium

30. Effect of Gut Activity on GI Blood Flow • Blood flow in each area of the GI tract is directly related to the level of activity • Possible causes of increased blood flow: • GI hormones (CCK, VIP, secretin, gastrin) • Bradykinin • Decreased oxygen concentration • Hypoxia related increase in adenosine

31. Countercurrent blood flow in the villi • Diffusion of O2 from the arterioles to venules in the villi • Short-cut circuit of 80% of O2

32. Microscopic View of the Wall of the Colon

33. Nervous Control of GI Blood Flow • Stimulation of parasympathetic nerves increases local blood flow at the same time that increases glandular secretion • Sympathetic stimulation, by contrast, causes vasoconstriction and decreases blood flow • Autoregulatory escape from the sympathetic stimulation – ischemia • Importance of nervous depression of GI blood flow when other parts of the body need extra blood

34. Feeting Tubes & Intravenous Feeding