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64 Cards in this Set
- Front
- Back
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What are alternate names for the entero-endocrine cells? (3) |
- Enterochromaffin-like cells (ECL) - Gastroenteropancreatic cells - Amine precursor uptake decarboxylase |
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Where do ANS nerves release NTs? |
onto varicosities |
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What are the 4 phases of gastric motility? |
- Cephalic phase - Gastric phase - Intestinal phase - Interdigestive phase |
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Where in the GIT is motor tone high all the time? |
The smooth muscle of the sphincters |
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What stimulates the cephalic phase? (4) |
Sight, smell, taste, and thought of food |
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What does Vagus stimulation of the stomach cause? (4) |
- Stimulates chief cells to secrete pepsinogen - Stimulates G cells to secrete gastrin - Stimulates ECL to secrete histamine - Indirectly stimulates parietal cells to secrete HCl |
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What is the major NT released by nerves of the ANS?
Onto what receptors in the GI do they bind? |
Acetylcholine
muscarinic receptors |
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How long after a meal does the cephalic phase continue to be stimulated? |
30 minutes |
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What stimulates gastric secretion of the stomach once food has arrived? (2) |
- Stomach distension - Amino acids and polypeptides in chyme |
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What does histamine do in the stomach? |
Stimulate HCl secretion |
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What positive feedback system is in place in stomach secretions? |
As acid eats away at chyme, more amino acids and polypeptides are released to further secrete more stuff |
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What negative feedback is in the stomach to inhibit secretions? |
As pH drops, it inhibits G-cell release of gastrin |
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What signals initiate the intestinal phase? (2) |
- Increase in osmolality - Distension |
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What effects does chyme have once it enters the duodenum? (2) |
- Inhibitory neural reflex upstream to inhibit gastric secretion and motility - Excitatory neural/hormonal reflex downstream to stimulate secretions from the pancreas, liver/gall bladder, and intestines |
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In the presence of fat in the intestines, what hormone class inhibits gastric secretions and motility? |
enterogasterone |
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What hormones are secreted by the intestines in the intestinal phase? (5) |
- Somatostatin - Secretin - CCK - Enterogastrone - GLP-1 |
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What cells set the pacemaker rhythm of the gut? |
Interstitial cells of Cajal |
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Through what does smooth muscle depolarization flow from cell-to-cell? (give the special name too) |
gap junctions called nexuses |
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What is the resting membrane potential of GI smooth muscle? |
Slow-wave oscillation between -60 mV to -30 mV |
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Is there tension in GI smooth muscle during the post-prandial period? |
Yes |
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What allows smooth muscle to perform work over a large range in all directions? |
High actin/myosin ratio |
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What 6 proteins connect GI smooth muscle cells? |
connexins (6 makeup a gap junction) |
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Where are interstitial cells of Cajal located? |
longitudinal smooth muscle |
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What are intermediate junctions? |
Proteins that connect adjacent GI smooth cells |
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What 2 proteins makes up intermediate filaments in smooth muscle? |
desmin and vimentin |
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What motion does a GI smooth muscle contraction take? |
Cork-screw movement |
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Does the GI smooth muscle cell have a sarcoplasmic reticulum? |
Yes, but it's very tiny, most Ca2+ comes from ECM |
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How many nuclei are there per visceral smooth muscle cell? |
1 |
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Do GI smooth muscle cells have T-tubules? |
No |
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What is the ratio of actin:myosin in gut smooth muscle? |
15:1 |
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What protein takes the place of troponin in GI smooth muscle cells? |
Calmodulin |
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What is stress relaxation (creep)? |
Smooth muscle will accommodate changes in lengths to maintain the same tension regardless of distention or relaxation |
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What influences the basal electrical rhythm of the GI smooth muscle? |
ANS innervation |
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What is the rate of EPSPs in GI smooth muscle relative to skeletal muscle? (qualitative) |
Much slower |
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What can influence the rate of APs in GI smooth muscle? (2) |
Neurotransmitters and Hormones |
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What effect does SNS have on BER? |
Decreases it |
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What effect does PNS have on BER? |
Increases it |
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In the GI, can a single neuron release more than one neurotransmitter? |
Yes |
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What NTs are released by SNS neurons onto the gut? (3) |
NE/Epi and DA |
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What effect does SNS innervation have on the gut? |
Inhibition of motility and secretion |
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What are the exceptions of gut inhibition by SNS exist? (2) |
- activates muscularis mucosa for protection of noxious substances at local sites
- increase in mucus secretion |
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Where is the myenteric plexus located? |
Between the longitudinal and circular muscle layers of the muscularis externa |
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Where is the submucosal plexus located? |
Outside the muscularis mucosa |
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Where are the PNS post-ganglionic cell bodies for the gut found? |
In the enteric nervous system |
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To which neurons does the term interneurons refer to in the gut? |
Submucosal plexus (Meissner's plexus) |
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What neurotransmitter do PNS nerves release? |
Acetylcholine |
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Why would PNS fibers have opposing effects on the lower esophageal sphincter? |
To allow food to move in via relaxation but to then close it tightly |
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What two neurotransmitters are responsible for transient relaxation of the lower esophageal sphincter and stomach? |
VIP and NO
(relaxation lasts only a few seconds) |
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How far does the control over and intramural plexus cell body reach? |
several cm |
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What do afferents detect from the gut? (5) |
- mechanoception - chemoception - pH - osmolarity - specific chemicals |
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What do regional reflexes do? |
Recruit more interneurons to affect a larger area of gut |
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What is the gastrocolic reflex? |
Stretching of the stomach leads to colonic motility |
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When inciting the gastrocolic reflex, where do signals from gastric afferents go to get to the smooth muscle of the colon? |
Gastric afferents --> interneurons --> celiac ganglion --> myenteric plexus of the colon --> smooth muscle of the colon |
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What is the intestino-intestinal reflex? |
If a region of the intestines becomes stretched, the rest of the intestine relaxes |
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If a reflex feeds back up the GI, what is its action typically? |
Inhibitory |
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If a reflex feeds forward, what is its action typically? |
Excitatory |
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What are some examples of central reflexes? (4) |
- Vomiting - Defecation - Gall bladder motility - Sensation of the gut |
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What skeletal muscles are involved in emesis? (2) |
Abdominal muscles and diaphragm |
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What does chronic vomiting cause? (3) |
- Metabolic alkalosis - Dehydration - Hypokalemia |
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Why does high nicotine doses lead to vomiting? |
Nicotine affects the area postrema to innervate nicotinic receptors |
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What is the vomiting center of the brain? |
NTS |
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What is retching? |
Almost vomit but upper esophageal sphincter remains closed |
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What is projectile vomiting?
Why does it occur in babies? |
Emesis without retching
pyloric stenosis |
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What occurs to BER from proximal to distal intestines? |
Decreases |
