Movements of the GIT and pancreatic secretions slides

Movements of the GIT & Pancreatic Secretions

Presented by Dr. Joe Quinn

By the end of this session you should be able to:

1) Explain how reflux from stomach to oesophagus is avoided

  • The lower oesophageal sphincter relaxes during swallowing, decreasing intraluminal pressure, which is termed receptive relaxation. This prevents reflux by maintaining a high pressure in the sphincter region.

2) Describe gastric emptying into the duodenum

  • Organised motility in the stomach is essential for orderly emptying of contents from stomach to duodenum

  • Involves mixing food with gastric secretions via strong peristaltic contractions in the antrum

  • These contractions are opposed by pylorus which regulates emptying

  • Strong contractions begin in the mid-stomach and spread to the caudad region, moving up and becoming six times more powerful as the stomach empties

  • Each strong wave forces chyme into the duodenum when pyloric tone is normal, effectively mixing contents and driving the pyloric pump.

  • The pyloric sphincter is a thickened region of circular muscle that normally remains closed.

  • It opens slightly to allow fluids to leave the stomach.

  • Chyme can only pass through when it has a sufficiently fluid consistency

  • The sphincter is influenced by nerves and hormones, with the duodenum exerting the most control over its function.

  • This control ensures chyme enters the duodenum at a regulated rate to prevent overloading.

  • Gastric emptying is promoted when the stomach wall is stretched, which activates reflexes that relax the pyloric sphincter

  • Enterogastric reflexes:

3) Describe the changes in pH that occur as food passes through the duodenum

  • As food enters the duodenum, the pH gradually changes due to the secretion of acidic gastric contents. The presence of alkaline pancreatic secretions later raises the pH, aiding in digestion.

4) Describe the regulation of pancreatic secretion

  • Regulation occurs through hormonal signals; acid in the stomach promotes secretin release, while fats and amino acids stimulate cholecystokinin. Both hormones prompt bicarbonate and enzyme secretion.

5) Describe the phases of pancreatic secretion

  • Cephalic Phase: Triggered by acetylcholine from vagal nerve endings leading to moderate enzyme release.

  • Gastric Phase: Continues nerve stimulation, resulting in small pancreatic juice reaching the duodenum.

  • Intestinal Phase: Characterized by secretin causing copious pancreatic secretion into the duodenum.

6) Explain the key role of pancreatic enzymes in digestion

  • Pancreatic enzymes are critical for the digestion of proteins (proteases and peptidases), carbohydrates (pancreatic amylase), and fats (lipase and cholesterol esterase). They are secreted as inactive precursors to prevent damage to the pancreas.

7) List the mixing and propulsive movements of the intestine

  • Intestinal movements include:

    • Segmentation Contractions: Mix content in the intestine initiated by stretch.

    • Peristalsis: A slow, propulsive force mediated by reflexes and hormones.

    • Migratory Motor Complexes: Sweeping actions in a fasted state to move contents towards the colon.

8) Explain the mechanism of vomiting including the roles of smooth and striated muscle

  • Vomiting is triggered by irritation or over-distension of the GIT, generating sensory signals that lead to motor impulses targeting the abdominal muscles and diaphragm, involving smooth and striated muscle.

9) Explain the basic reflex arc involved in vomiting and how it can be influenced by higher centres

  • The reflex arc involves sensory input from the GIT to the central nervous system, which coordinates motor output for vomiting, modulated by higher brain centres based on emotional or sensory stimuli.

10) Explain the basic reflex arc involved in defecation and how it is influenced by higher centres

  • The defecation reflex activates stretch receptors in the rectal wall, leading to increased colonic activity and relaxation of the internal anal sphincter, influenced by signals from higher centres in the brain. It creates a conscious urge to defecate.