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GI Part 1-2
GI part 1-2 highlights
Question | Answer |
---|---|
What happens if you cut the vagus nerve? | De-nervated gut can still function through the Enteric nervous system |
Difference between endocrine, paracrine, neurocrine and immune cells | Endocrine: travel through blood, paracrine travel through fusion, neurocrine is a mediator out of nerve cell and immune cells are for the immune response |
Name the 6 sphincters in the GI tract | Upper esophageal, lower esophageal, pyloric, internal rectal, external rectal, ileocecal |
Myenteric/Auerbach's plexus | B/w circular and longitudinal layer of muscle. Found from esophagus to rectum. Control of muscle function |
Sumucosal/Meissner's plexus | From small intestine to colon, secretal function. Control of mucosal function |
Are the ganglions in the plexuses of the Enteric system? | No |
Do fibers go to myenteric plexus first 100% of the time? | Some fibers from myenteric plexus go to submucosal plexus while others may go Directly to submucosal plexus. |
Where do the afferent fibers feed into? | They feed back into submucosal plexus & have connections that feed into myenteric plexus. Afferents can go directly to CNS (long reflex) & cause reflex input in vagus or sympathetic fibers back to ENS. |
Where do the bulk of Sympathetic nerves synapse? | Bulk synapses in myenteric plexus. Some go directly to secretory cells, sphincters or vascular cells |
Where do the parasympathetic nerves synapse? | In the myenteric plexus |
Name the 5 established GI hormones | Secretin, gastrin, CCK, GIP & motilin |
Gastrin | Found in antrum primarily down to jejunum. Causes acid secretion |
CCK | Found in Dudodenum & jejunum primarily down to ilieum. Causes gallbladder to contract and pancreas to secrete |
Secretin | Comes from S cells in duodenum & jejunum primarily down to ileum. Causes bicarbonate secretion. Stimulated by acid secretion |
GIP | Stimulated by osmolality, lipids. Causes insulin release from pancreas in the presence of glucose in the plasma. Found in duodenum and jejunum. |
Motilin | Found in duodenum and jejunum. Enhances motility |
Name the myenteric neurons that are stimulatory motor neurons | Ach |
Myenteric inhibitory neurons | NO and VIP (often co-released). VIP= vaso intestinal peptide |
Myenteric interneurons | Ach & 5-HT= 5-Hydorxytryptamine |
Myenteric sensory neurons | Substance P |
Somatostatin | From D cells in antrum. Acid stimulates release. Targets G cells and inhibits gastrin release |
Histamine | Found in ECL cells and mast cells. Stimulated by Ach, gastrin and antigens. Targets parietal cells ad mucosal crypt cells. Secretes acid and Cl- |
Adenosine | Comes from various cells, regulates intestinal secretion and vascular |
5-HT | Comes from enterochromaffin cells. Involved in secretion and absorption |
Does Gastrin or CCK favor CCK-A receptor? CCK- B receptor? | CCK-A strongly favors CCK. Gastrin needs CCK-B receptor. Both favor CCK-B the same |
Glucagon, GIP and VIP similarity to secretin | Glucagon= 1/2 same. GIP= 9 the same. VIP= 1/3 the same as secretin |
What 2nd messenger do glucagon, GIP, VIP and secretin act through? | cAMP |
What 2nd messenger does gastrin and CCK act through? | Calcium |
Slow Wave | Regular, spontaneous, rhythmic cycles of de and repolarization. Not action potentials |
Plateu of slow wave | Ca influx=K deflux |
Origin of slow waves | Interstitial Cells of Cajal which have spontaneous pace maker currents. NO ICC's=no BER |
Gap junctions in visceral smooth muscle | Depolarization spreads from ICC to VSM |
Functions of ICCs | Mediate some neural responses of the muscle. Propagate longitudinally along longitudinal muscle layer, and then to circular muscle layer |
What does L-NA abolish? | NO induced ISP |
What does Neostigmine do? | Prevents Ach breakdown which leads to slower late depolarization |
What happens when you stimulate tissue? | Slow wave becomes longer, perhaps larger and more Ca enters cell therefore it is a stronger contraction |
Are slow waves always present? What enhances them? | Yes. Presence of Ach or parasympathetic nerve activity enhances them. Enhanced slow wave translates into contractions--peristalic wave |
How often does a new wave start? | Everything progresses caudally & increases in velocity as they progress toward pylorus. A new wave starts every 12-20 seconds. |
Can slow waves give rise to APs? | They might or might not reach threshold and give rise to true APs |