Lecture 5 (DSA): Motility of the GI tract Flashcards
What are the functional layers of the GI tract?
- Mucosal layer
- Submucosa
- Muscle layers: Circular and logitudinal
- Serosa
What is the enteric NS and why is it special?
- Submucosal and Myenteric plexuses
- Can exert its functions w/o CNS input
What type of information does the ENS receive?
- Info from parasympathetic, sympathetic, and CNS
- Sensory info from mechanoreceptors and chemoreceptors in the mucosa
Parasympathetic innervation of the GI is modulated by which nerves; where are the pre- and post-ganglionic fibers located; what type of receptor?
- Vagus and Pelvic splanchnic’s
- Pre-ganglionic cell bodies located in brainstem and sacral spinal cord
- Post-ganglionic neurons in the wall of the organ (enteric neuron in the gut wall)
- Synapse uses a nAChR
How does sympathetic innervation of the gut work in terms of the pre- and post-ganglionic fibers; what is the NT released by each?
- Pre-ganglionic efferents arise within spinal cord and end on pre-vertebral ganglia. The post-ganglionic fibers then go on to innervate myenteric and submucosal plexuses.
- Pre-ganglionic’s release ACh, while post-ganglionic’s release NE
What are examples of paracrine molecules, where do they act, and how do these signals reach their targets?
- Somatostatin and histamine
- Act locally
- Reach targets by diffusion over short distances
What cells secrete somatostatin, what is the stimulus for this secretion, and what is the action of this hormone?
- Secreted by D cells of the GI mucosa
- Stimulated by decreased luminal pH
- Inhibits gastric H+ secretion and secretion of other GI hormones
What cells secrete histamine, what is its target, and what is the action of this hormone?
- Enterochromaffin-like cells (ECL) in gastric glands
- Acts on parietal cells to stimulate acid production
How does endocrine regulation work?
Enteroendocrine cells contain secretory granules filled w/ hormones that are released into the circulation upon stimulation
Where is gastrin secreted from, stimuli, and actions?
- G cells of the stomach
- Stimulated by peptides, AA, distention, and vagus via GRP
- Increases gastric H+ secretion and stimulates growth of gastric mucosa
Where is CCK secreted from, stimuli, and actions?
- I cells of the duodenum and jejunum
- Stimulated by small peptides, AA, and FA’s
- Increase pancreatic enzyme secretion, HCO3- secretion, stimulates contraction of gallbladder and relaxation of the sphincter Oddi, stimulates growth of the exocrine pancreas/gallbladder, and inhibits gastric emptying
Where is secretin secreted from, stimuli, and actions?
- S cells of the duodenum
- Stimulated by H+ and FA’s in the duodenum
- Increases pancreatic HCO3- secretion, biliary HCO3- secretion, decreases gastric H+ secretion, and inhibits trophic effect of gastrin on gastric mucosa
Where is glucose-dependent insulinotropic peptide (GIP) secreted from, stimuli, and actions?
- Duodenum and jejunum
- Stimulated by FA’s, AA’s, and Oral glucose
- Increases insulin secretion from pancreatic β cells, and decreases gastric H+ secretion
Which hormones of the GI tract can act as paracrine signals?
CCK, Secretin, Somatostatin, and Histamine
What would be more effective in increasing insulin secretion:
a) Oral glucose administration
b) IV glucose administration
a) Oral glucose stimulates GIP, which stimulates insulin secretion, and also have DIRECT stimulatory effects on β cells of pancreas
