Control of the GI System PDF

Control of the GI system Lecture Number 2.2 Status Done Type Lecture 2.2 Control of the GI system Overview This lecture discusses the regulation and control of the gastrointestinal system, focusing on smooth muscle function, gastrointestinal motility, and th...

Control of the GI system Lecture Number 2.2 Status Done Type Lecture 2.2 Control of the GI system Overview This lecture discusses the regulation and control of the gastrointestinal system, focusing on smooth muscle function, gastrointestinal motility, and the involvement of the enteric nervous system in health and disease. It covers the role of the interstitial cells of Cajal, splanchnic circulation, gastric peptides, and the physiological relevance of the incretin response, as well as mechanisms such as nausea and vomiting. Learning Objectives Objective 1: Understand the role of the enteric nervous system in GI motility and secretion. Objective 2: Explore the regulatory functions of splanchnic circulation. Objective 3: Examine the role of gastrointestinal peptides and hormones, such as GLP-1, in digestion and metabolism. Objective 4: Investigate the mechanism and control of vomiting as a defence mechanism in the GI tract. Key Concepts and Definitions Enteric Nervous System (ENS): A complex system embedded in the GI tract, controlling motility and secretion independently from the CNS. It consists of two main plexuses: the myenteric plexus (Auerbach's) and the submucosal plexus (Meissner's). Splanchnic Circulation : Refers to the blood flow to the stomach, intestines, liver, and pancreas. It plays a vital role in nutrient absorption, and its regulation is crucial for maintaining homeostasis. Interstitial Cells of Cajal (ICC): Pacemaker cells that generate slow waves to regulate GI smooth muscle contractions. Incretins: Hormones, such as GLP-1, that enhance insulin secretion in response to food intake and help regulate glucose metabolism. Clinical Applications Case Study: A 60-year-old male presents with delayed gastric emptying (gastroparesis), potentially linked to a loss of ICC function. Understanding the regulation of motility by the ENS helps in diagnosing conditions like gastroparesis. Diagnostic Approach: In cases of GI motility disorders, key diagnostic steps include manometry, which assesses muscle contractions, and imaging for splanchnic blood flow. Treatment Options: Pharmacological treatments for motility disorders may involve prokinetics that enhance smooth muscle contractions or interventions aimed at regulating blood flow in splanchnic circulation. Complications/Management: Managing complications such as nausea and vomiting involves understanding the neural circuits responsible for emesis. Pathophysiology Enteric Nervous System (ENS) Dysfunction : Damage to the ENS, as seen in conditions like diabetes, can lead to dysregulation of peristalsis, leading to conditions like gastroparesis. The loss of normal pacemaker function from the ICCs can result in abnormal slow-wave patterns, leading to delayed gastric emptying. Vomiting Mechanism : Vomiting is a reflex triggered by afferent signals from the GI tract to the brainstem's "vomiting centre." Phases of vomiting include reverse peristalsis, contraction of abdominal muscles, and relaxation of the oesophageal sphincter, coordinated by both the ENS and CNS. Pharmacology Prokinetic Drugs: Medications like metoclopramide enhance GI motility by increasing the action of acetylcholine on muscarinic receptors, which stimulates smooth muscle contraction. Antiemetics: Drugs such as ondansetron block serotonin receptors in the vomiting centre of the brain, used to treat nausea and vomiting. (5HT3 antagonist, serotonergic) Differential Diagnosis Gastroparesis: Delayed gastric emptying due to damage or dysfunction in ICCs or the ENS. Key symptoms include nausea, vomiting, and bloating. Irritable Bowel Syndrome (IBS): A disorder affecting the large intestine with symptoms of abdominal pain, bloating, and changes in bowel habits. It can be distinguished from motility disorders by the presence of normal GI structure but altered function. Investigations GI Manometry: Measures the contractions of GI muscles to assess abnormalities in peristalsis, especially in disorders like gastroparesis or oesophageal motility issues. Splanchnic Doppler Ultrasound: Used to assess blood flow to the digestive organs, especially in conditions involving altered blood supply like ischemia. Key Diagrams and Visuals Summary and Key Takeaways The enteric nervous system regulates GI motility and secretion independently but interacts with the CNS. Splanchnic circulation is essential for nutrient absorption and GI function. Interstitial cells of Cajal act as pacemakers, regulating smooth muscle contractions in the GI tract. Understanding the control of nausea and vomiting requires knowledge of both central and peripheral pathways. Further Reading/References Ganong’s Review of Medical Physiology – Chapter on the gastrointestinal system and its control mechanisms. Guyton and Hall Textbook of Medical Physiology – Detailed explanation of the enteric nervous system and splanchnic circulation. Questions/Clarifications What is the role of the gut microbiome in influencing the enteric nervous system? How does splanchnic blood flow affect digestion in pathological conditions like portal hypertension?