1 III GASTRIC MOTILITY

2 Major Function of Gastric Motility  To serve as a reservoir  To break food into small particles and mix food with gastric secretions  To empty gastric contents into the duodenum at a controlled rate

3 1. Anatomy and innervation of the Stomach

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5 The stomach can be divided into three anatomic regions (A) and two functional regions (B) Gastric reservoir Tonic contractions Gastric reservoir Tonic contractions Gastric pump Phasic contractions Gastric pump Phasic contractions B B Fundus Corpus Antrum Pylorus A A

6 Oesophagus Lower Oesophageal Sphincter Fundus Body Antrum Duodenum Pylorus Functional Anatomy of Stomach Fundus Body Antrum Storage Mucus HCl Pepsinogen Intrinsic factor Mixing/Grinding Gastrin

7 Anatomy

8 Innervation of the GI tract

9 2. Responses to Gastric Filling – Receptive Relaxation

10 Receptive relaxation During chewing and swallowing food, the stimulation of food to the receptors in mouth, pharynx, and esophagus reflexly causes the smooth muscle of the fundus and body of the stomach to relax, This process allows the stomach to accommodate a large amounts of food and fluid.

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12 The relaxation of the gastric reservoir is mainly regulated by reflexes. Three kinds of relaxation can be differentiated: the receptive, adaptive and feedback-relaxation Inhibitory vagal fibre (NANC-inhibition) Nutrients CCK Relaxation of gastric reservoir ACH Vagus centre 1. Receptive relaxation Mechanical stimuli in the pharynx 3. Feedback relaxation 2. Adap tive relax ation Nutrients Tension receptors Distension NO + VIP et al.

13 3. Peristalsis of the Gut and Gastric Emptying

14 Gastric Motility Peristaltic waves: Body  Antrum Body Thin muscle  weak contraction  No mixing Antrum Thick muscle  powerful contraction AMixing BContraction of pyloric sphincter  1Only small quantity of gastric content (chyme) entering duodenum 2Further mixing as antral contents forced back towards body

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16 What produces gastric peristaltic waves? Peristaltic rhythm (~3/min) generated by pacemaker cells (longitudinal muscle layer) Slow waves – spontaneous depolarisation/ repolarisation Slow wave rhythm = basic electrical rhythm (BER) Slow waves conducted through gap junctions along longitudinal muscle layer Slow wave depolarisation sub-threshold - require further depolarisation to induce action potentials  contraction Number of APs/wave determines strength of contraction

17 Gastric Slow Waves and Motility

18 peristalsis

19 Peristalsis Figure 24.4

20 The contraction of the gastric pump can be differentiated into three phases: A: phase of propulsion, B: phase of emptying, C: phase of retropulsion and grinding Retropulsion of large particles and clearing of the terminal antrum

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22 Control of gastric motility Vagovagal reflex – fundal relaxation Myenteric plexus – slow waves – contraction Parasympathetic and Gastrin – increase contraction force and frequency Sympathetic – decrease contraction force and frequency

23 Gastric emptying 1. Def. The process by which the chyme is expelled from the stomach into the duodenum is called the gastric emptying. 2. Control 1) stomach: stimulating factor, neuronal and hormonal 2) duodenum: inhibiting factor entero-gastric reflex, hormones

24 Control of Gastric emptying Stimulating factors in stomach Presence of food Gastrin

25 Control of gastric emptying

26 Balance between gastric reservoir and antral pump Gastro-gastric reflexes Enhanced and prolonged relaxation of reservoir Distension Disten- sion Excitatory reflex Antral pump switched on and intensified Inhibitory reflex

27 Inhibitory effects in duodenum and jejunum – throug refelxes and hormones Inhibitory reflexes – direct – myenteric plexus indirect – via extrinsic nerves Neural reflexes stimulated by: Distension, irritation, acidity, high osmolarity, protein/fat Fats and acids also stimulate release of humoral factors which reduce gastric emptying Cholecystokinin (CCK), stimulated by fats Secretin, stimulated by acids Control of Gastric emptying

28 Enterogastric Reflex regulates the rate at which chyme leaves the stomach

29 The feedback regulation of gastric emptying is performed by entero-gastric reflexes and release of intestinal hormones Ehrlein Figure 14 Ehrlein Figure 14 It causes enhanced relaxation of the gastric reservoir, inhibition of the antral pump, and reduced opening of the pyloric sphincter. Vagal center Inhibitory vagal fibers NO, VIP et al. Sensoric afferent fibers CCK ACH Enhanced relaxation and storage Stimulating cholinergic vagal fibers Nutrients Long chain fatty acids Amino acids Dipeptids Glucose Osmolality Hydrochloric acid Reduced opening of pyloric sphincter Reduced contraction Backflow + + _ ACH

30 non-digestible spheres “Quality” of food regulates gastric emtying

31 Solids and liquids of the gastric chyme are emptied with different velocities. Lag phase Time (min) Viscous content Liquid content Solids Gastric volume (%) Emptying of liquids is exponential. Emptying of large solid particles only begins after sufficient grinding (lag phase). Afterwards the viscous chyme is mainly emptied in a linear fashion

32 4. Vomiting Emesis Stretching, toxins, alcohol, spicy foods, and drugs may stimulate this. Emetic Center of the Medulla Diaphragm and abdominal wall contract Cardiac sphincter relaxes. Soft palate rises