Term
| Three most important functions of the stomach and their mediators |
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Definition
1. Digestion: main macronutrient digested is protein using HCL (parietal cells) and pepsinogen (chief cells). HCl cleaves pepsinogen-->pepsin at polypeptide site of aromatic amino acids.
2. Vitamin B12 absorption: Intrinsic Factor from parietal cells transports B12 from stomachinto terminal ileum.
3. Gastric reservoir: w/out it dumping syndrome occurs, which is a rapid release of hyper osmolar products into duodenum. Typical after gastrectomy, symptoms: N/dizziness, diarrhea, and diaphoresis. |
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Term
| Three phases of gastric acid production |
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Definition
1. Cephalic phase: cholinergic and vagal mechanisms
2. Gastric phase: mediated by gastrin, triggered by chemical stimulus of food and stomach distension.
3. Intestinal phase: initiated by protein in the duodenum |
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Term
| Receptive relaxation of the stomach |
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Definition
Mechanoreceptors detect stretch.
Afferent signal to brain mediated by vasovagal reflex (afferent-->efferent)
VIP released from postganglionic vagal nerve fibres (inhibits smooth mm action=relaxation) |
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Term
| Gastric Emptying and the two factors that slow it: |
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Definition
Takes approximately 3 hours on average.
Rate of emptying is highly regulated to allow enough neutralization of duodenal acid to allow for optimal absorption.
Factors slowing gastric emptying:
1. Presence of fat in the stomach stimulates CCK (satiety hormone) to slow down emptying.
2. Presence of acid (H+) in duodenum |
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Term
| HCl: what it does, where it comes from? |
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Definition
lowers pH=pepsinogen cleaved into pepsin.
Synthesized in parietal cells of the gastric mucosa (H/K ATPase) |
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Term
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Definition
| Need a decrease in pH (acidity) to be converted into pepsin. |
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Term
| Intrinsic factor function |
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Definition
Binds B12 and takes it to the terminal ileum.
From parietal cells |
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Term
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Definition
| Mechanical barrier against acid. |
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Term
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Definition
Stimulated by gastrin, histamine, and ACh.
Aerobic metabolism accounts pumping of H+ and Cl into lumen
1st: CO2+ H20 make H2CO3 which further breaks down into H+ and HCO3(bicarbonate)
2nd: H+ in lumen combines with Cl that was pumped out through transmembrane protein.
3rd: bicarbonate is pumped out to BV's. |
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Term
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Definition
| Stimulated to be released by distension of antrum. |
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Term
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Definition
Is a neuroendocrine tumor that hypersecretes gastrin which is released into circulation.
MC seen from peripancreatic, pancreatic tissues,and duodenum.
Presence of a jejunal ulcer is highly suspect for a gastrinoma.
MEN1: PTH, CA, Pituitary issues, and a Gastrinoma tx with PPI. |
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Term
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Definition
Mucus is the physical barrier.
Prostaglandins produces mucus from Arachidonic Acid cycle; inhibited by ASA and steroids (block COX1)
HCO3: neutralizes any excess acid. |
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Term
| Prostaglandin (drug forms) |
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Definition
1. Misoprostol: ideal when NSAI induced deficiency
2. Alprostadil: used to keep open a PDA in newborns (both do this) |
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Term
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Definition
Release HCl and intrinsic factor. Canbe stimulated by:
1. Vagus: stimulates M3 (muscarinic) recepotrs
2. Mast Cells: histamine receptor (H2)
3. G-cells: gastrin receptor |
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Term
| Vagal stimulation of parietal cells |
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Definition
M3 inhibited by atropine
The Vagus nn sends ACh to bind M3 which releases HCl. |
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Term
| Mast cell/histamine receptor stimulation of parietals |
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Definition
Blocked by anti-histamines
Mast cells release histamine which binds H2 receptor which releases HCl |
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Term
| G-cells and gastrin interacting with parietal cells |
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Definition
| Gastrin receptor increases Ca++ which stimulates HCl release. |
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Term
| Parietal cells: where can we find them? |
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Definition
| Mucosal glands of body and fundus: eosinophilic cytoplasm, increase in mitochondria, tubulovesicular system. |
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Term
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Definition
An erosion only gets through the mucosal layer.
Ulcerations penetrate mucosa all the way to submucosa, d/t NSAIDs or ASA use.
Remember layers of GI: Mucosa-->Muscularis-->Submucosa--> Muscularis--> serosa |
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