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GI Part 1-2

GI part 1-2 highlights

QuestionAnswer
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