GI Physiology VSAQs

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### Sham Feeding - A procedure where food is ingested and chewed but prevented from entering the stomach (e.g., via an esophageal fistula). - Used to study the cephalic phase of digestion, demonstrating neural control over gastric and pancreatic secretions. - Stimulates gastric acid, pepsin, and pancreatic enzyme secretion through vagal pathways. ### Succus Entericus - Also known as intestinal juice, secreted by the glands of Lieberkühn in the small intestine. - Composed of water, electrolytes, mucus, and enzymes (e.g., peptidases, disaccharidases, nucleosidases). - Provides a fluid medium for digestion and absorption, and its enzymes complete the digestion of carbohydrates, proteins, and nucleic acids. ### GI Hormones - Chemical messengers secreted by enteroendocrine cells in the GI tract, acting on distant target cells. - Examples include Gastrin (stimulates gastric acid), Secretin (stimulates bicarbonate from pancreas/liver), CCK (stimulates gallbladder contraction, pancreatic enzymes), GIP (stimulates insulin release), and Motilin (initiates MMC). - Regulate various GI functions like motility, secretion, absorption, and growth of the digestive organs. ### Hirschsprung Disease - A congenital condition characterized by the absence of ganglion cells (Auerbach's and Meissner's plexuses) in a segment of the colon. - Results in a tonically contracted, aganglionic segment that cannot relax, leading to functional obstruction and proximal dilation. - Causes severe constipation, abdominal distension, and potentially life-threatening enterocolitis in newborns. ### Gastrocolic Reflex - A physiological reflex that increases motility of the colon in response to distension of the stomach by food. - Mediated by both neural (vagal and intrinsic enteric nervous system) and hormonal (e.g., gastrin, CCK) pathways. - Plays a role in mass movements in the colon, often leading to the urge to defecate after a meal. ### Gut Microbiota - The diverse community of microorganisms (bacteria, fungi, viruses, archaea) residing in the gastrointestinal tract. - Contributes to digestion (e.g., fermentation of indigestible carbohydrates, vitamin K synthesis), immune system development, and protection against pathogens. - Imbalances (dysbiosis) are linked to various health conditions, including inflammatory bowel disease, obesity, and metabolic disorders. ### Migrating Motor Complex - (MMC) — A pattern of electrical and motor activity that occurs in the stomach and small intestine during fasting. - Consists of distinct phases: quiescence, irregular contractions, and a burst of intense, propagating contractions. - Functions as the "housekeeper" of the gut, sweeping undigested food particles, bacteria, and secretions from the stomach to the colon between meals. Initiated by Motilin. ### Achalasia Cardia - A motor disorder of the esophagus characterized by impaired relaxation of the lower esophageal sphincter (LES) and loss of peristalsis in the distal esophagus. - Caused by degeneration of inhibitory neurons in the myenteric plexus of the esophageal wall. - Leads to difficulty swallowing (dysphagia) for both solids and liquids, regurgitation of undigested food, and chest pain. ### Gastric Emptying - The process by which food is propelled from the stomach into the duodenum. - Regulated by complex interactions between gastric distension, duodenal nutrient content (fat, acid, osmolarity), and hormonal/neural reflexes. - Typically, liquids empty faster than solids, and fats significantly slow emptying due to the action of hormones like CCK and GIP. ### Law of Gut - Also known as the "Law of the Intestine" or "Bayliss and Starling's Law of the Intestine." - States that stimulation at any point in the intestine causes contraction of the musculature above that point and relaxation below it, facilitating aboral movement of contents. - This intrinsic property of the enteric nervous system ensures unidirectional propulsion of chyme through the GI tract.