MOTILITY OF THE GUT

1. MOTILITY OF THE GUT

3. PACEMAKER OF THE GUT It is a thin layer of interstitial cells ; interstitial cells of Cajal, lying between circular and longitudinal cell layer.

4. interstitial cells of Cajal It is characterized by: a slow wave activity gap junctions tight synapses with enteric nerves

5. PACEMAKER OF THE GUT Insert fig. 18.16

6. Electro-physiology of smooth muscles of the GUT

7. Resting membrane potential Itis -50 to - 60 mV with potential oscillations

8. Slow Waves = Pacemaker Potential = Basic Electric Rhythm (BER) It is spontaneous rhythmic fluctuation in the smooth muscles membrane potential between – 60 mv & – 40 mv. Itisinitiated by the interstitial cells of Cajal

9. They are not followed by muscle contraction unless they reach a threshold for the spike potentials. Pacemaker potential

11. Pacemaker zone of the stomach

12. The action potentials (spike potentials) is produced when slow-waves reach the threshold automatically due to Opening of L-type calcium channels This is induced by Stretch of smooth muscle, vagal stimulation, hormones or myenteric plexus stimulation.

13. 1- nervous stimulation 2- distension (stretch) 3- hormones

14. Enteric nervous system (gut brain)

15. Enteric nervous system (gut brain)

16. Enteric nervous system (gut brain) The myenteric plexus has Sensory receptor neurons Motor effector neurons The neurotransmittors Excitatory & Inhibitory

17. Functional types of movements in GIT

19. vagal stretch irritants ++Enteric neurons Peristalsis Contractile rings

20. Peristalsis

21. Peristalsis This signal is transmitted by interneurons Excitatory (proximal) motor neuron Inhibitory (distal) motor neurons, bolus is transported in oral to caudal direction

24. Mixing movement They are local intermittent constrictive contractions occur every few cms in the gut wall, lasts only 5 -30 seconds then new constrictions occur at other points keeping the contents thoroughly mixed together

25. Mixing movement

26. Patterns of motility

27. Tonic contractions continuous contractions with different intensity lasts minutes to hours. It is caused by continuous repetitive spike potential, any factor causes continuous partial depolarization, or by hormones. It is usually occurs at the sphincteric regions •

28. Hunger contraction It is rhythmical continous tetanic intense prestalsis on empty stomach, lasts 2-3 minutes in young. It may cause mild pain in the pit of stomach, hunger pange especially after 12 hours – 4 days of starvation then it is gradually weakened.

29. Receptive relaxation of the stomach: When the esophageal peristalsis approaches the stomach , a wave of relaxation occurs in the entire stomach to the duodenum to prepare to receive food. It is due to ++ of myentric inhibitory neurons.

30. Reverse peristalsis (antiperistalsis) It is peristaltic waves occur in the reverse direction usually between stomach and duodenum and between ileum and cecum

31. Propulsive peristalsis: It is the basic movements occurs in esophagus, lower 2 thirds of stomach, small and large intestine, and rectum

32. Peristaltic rushirritation of small intestine results in powerful peristalsis travel the whole intestine in minutes to sweep its contents e.g., as on cases of infectious diarrhea

33. Haustration (segmentation of the colon)it is simultanous strong contraction of the circular muscles and teniae coli of the colon results in out plugging of the distal part to allow dug into and roll over the fecal material to absorb fluid and dissolved substances

34. Mass movements It is peristalsis in the colon 1-3time/day. 20 cm distal to the constrictive ring loses haustrations and contract as a unit to propel the fecal content in mass then inhibited to be returned after hours mediated by autonomic fibers. It appear after meals facilitated by gastro-colic and ilio-colic reflexes.

35. It is a fasting long peristalsis every 60-90 minutes from the stomach to the terminal ileum. It sweeps any undigested food in preparation for the next meal & helps to prevents bacteria from remaining in the small intestine Migrating motor complex (MMCs):

36. It is the mechanical processing of food and made it ready to swallow Mastication (chewing) Grinding Breaking Mixing é saliva Softening

37. it is important for digestion of all foods To increase the total surface area exposed to the digestive secretions Mastication (chewing) To break the cellulose of raw vegetables and fruits • To protect the wall of GIT

38. chewing process is controlled by nuclei in the brain stem Mastication (chewing) The muscles of chewing are innervated by the motor branch of V

39. Mastication (chewing) It starts voluntarily but continues as involuntarily reflex; a chewing reflex Once/sec

41. Primary peristalsis To sweep the oesophagus Types of esophageal peristaltic 8 - 10 sec • Secondary peristalsis distention of the esophagus myenteric circuit & by reflexes

42. Deglutition (swallowing) The start is voluntary, but it is completed reflexly. It is the transfer of food from the mouth to the stomach. The speed of swallowing depends on the consistency of food.

43. The voluntary phase: The pharyngeal phase: Phases of deglutition The oesophageal phase:

44. The voluntary phase: Phases of deglutition

45. The pharyngeal phase: contraction of the constrictor muscles of the pharynx occurs accompanied by receptive relaxation of the upper esophageal sphincter. Phases of deglutition

47. The pharyngeal phase: The posterior pillars approximate to shut off the mouth cavity Phases of deglutition Protective reflexes: