GI system: L31 - Revision lecture + Neurohormonal mechanisms Flashcards
What is the difference between the Enteric Nervous System and Central Nervous system in terms of neural regulation of the GI system?
The ENS is the primary neural system for controlling GI function and is independent - short, local, GI reflexes. The CNS modulates activity of ENS and has long neural reflexes.
What is the role of the ENS in GI regulation?
Consists of submucosal plexus (at the submucosal layer) which regulates secretion, and myenteric plexus (at the smooth muscle layer) regulates motility.
How are GI reflexes initiated? How is this mediated?
Distension, acidity of chyme, osmolarity of chyme, presence of products of digestion. Mechanoreceptors (distension), chemoreceptors (composition of lumen), osmoreceptors (osmolarity of lumen).
What is the role of CNS in GI regulation?
This is extrinsic (outside walls of GI tract) bidirectional regulation of GI function. Parasympathetic stimulates motility and secretion while sympathetic nervous system inhibits this.
What are some examples of reflexes?
Vagovagal reflex (vagus nerves) is a loop from vagal sensory afferents to CNS to vagal motor efferents. This includes gastric receptive relaxation, gastroileal reflex (clears intestine to make way for food). Intestino-intestinal reflex inhibitory motor reflex initiated by intestinal distension (enlargement). Involves thoracolumbar neural pathways (sympathetic).
What are the roles of gastrointestinal peptide hormones used to regulate GI function?
Gastrin - allows acid secretion, increases stomach motility and pepsinogen secretion.
Secretin - Inhibits acid secretion and stimulates bicarbonate and bile ejection from gallbladder.
Cholecystokinin - Inhibits acid secretion and stimulates secretion of pancreatic enzymes and ejection of bile from gallbladder, antagonist to gastrin.
Gastric inhibitory peptide - allows fatty acid metabolism, stimulates insulin secretion.
