Exam 4: Gastric Secretion Flashcards
What are the 3 muscle layers of the stomach?
Outer longitudinal layer
Middle circular layer
Inner oblique layer
What is receptive relaxation?
When distention of the lower esophagus relaxes the LES and also orad stomach
Other than receptive relaxation, what else relaxes the LES?
- Vasovagal reflex (afferent and efferents carried by vagus)
- VIP induced relaxation, released by vagus
What are gastric pits also known as and where in the stomach are they found?
Aka oxyntic glands
In the body of the stomach
Where in the stomach are pyloric glands found? What kind of cells do they contain?
Found in the antrum
Contain G cells and mucous neck cells
Where are chief cells found and what do they secrete?
Body of stomach
Pepsinogen
Where are parietal cells found and what do the secrete?
Body of stomach
HCL and intrinsic factor
Who do G cells secrete?
Gastrin
What do mucus cells secrete?
Mucus and pepsinogen
What are the 4 major components of gastric juice?
HCL, pepsinogen, mucus, and intrinsic factor
What does HCL in the stomach do?
Reduces the pH, activates pepsin, aids in protein digestion, and kills bacteria
What does pepsinogen do in the stomach?
Digests proteins
**pepsinogen is inactive, pepsin is active
What does mucus do in the stomach?
Protects the gastric mucosa from the corrosive actions of HCl
What does intrinsic factor do in the stomach?
Necessary for absorption of Vitamin B12 in the ileum
In the formation of HCl, what enzyme catalyzes the formation of H and HCO3?
Carbonic anhydrase
Where does HCl formation take place?
Gastric parietal cells
In HCL formation, after H is made via carbonic anhydrase, H is moved into the lumen in exchange for ** via **.
This is blocked by what drug?
K+
ATPase
Omeprazole
How does Cl get into the gastric parietal cells, so it can ultimately move across the apical membrane and form HCl?
Cl is exchanged for HCO3 on the basolateral membrane
What is the function of gastrin?
- stimulate acid and pepsinogen secretion
- stimulate growth of gastric and intestinal mucosa
- stimulate natural and intestinal motility
Gastrin is released from G cells of the antrum when stimulated by what 3 things?
- small peptides and amino acids in the stomach
- distention of stomach
- vagal stimulation
What inhibits gastrin release?
Low ph (<3), somatostatin, and PGE2
What are the 3 things that stimulate HCl release?
1) Gastrin stimulates partial cells via CCKb receptor
2) Gastrin stimulates ECL cells which release histamine, which bind to an H2 receptor on parietal cells
3) ACh
What is the treatment of H. Pylori?
Antibiotics (clarithromycin or amoxicillin)
What kind of drugs are Cimetidine and Ranitidine?
H2 blockers
What kind of drugs are omeprazole and lansoprazole?
PPIs
What causes peptic ulcer disease?
- Excess acid secretion and/or damage to mucosal barrier (acid destroys mucosal cells and liberates histamine and histamine stimulates acid secretion
- NSAIDS, inhibit COX and decrease PGs
- H. Pylori infection
What causes vomiting to occur?
- The diaphragm lowers to the inspiratory position and the glottis closes
- abdominal wall muscles contract increasing intra-abdominal pressure
- stomach, esophagus, and LES relax and stomach gets squeezed between diaphragm and viscera
- UES relaxes and vomit is projected into mouth
How do ECL cells play a role in HCl secretion?
Gastrin stimulates ECL cells, which release histamin, which binds to H2 receptors on the parietal cells
How does Atropine block HCl secretion?
It blocks M3 receptors
-when the vagus nerve releases ACh, atropine blocks the receptor that ACh is supposed to bind to
How is HCl secretion controlled in the cephalexin phase?
- PNS via the vagus directly stimulates parietal cells and also stimulates G cells to release gastrin
- Gastrin conveyed by circulation, stimulates parietal cells
What do the PNS nerves release in the cephalic phase that stimulate G cells to release gastrin?
Gastrin releasing peptide (GRP)
What stimulates HCl release in the gastric phase?
- release of amino acids and small peptides from parietal cells
- distention of the stomach by local and vagovagal reflex arcs
- histamine via H2 receptors
- Alcohol and caffeine
Is more HCL release in the gastric or cephalic phase?
Gastric
What is pepsinogen released from?
Chief cells
What converts inactive pepsinogen to its active form pepsin?
Acid, optimum pH is 1.5-2 and is denatured at 7
What is the function of pepsin?
Cleave proteins to peptides at aromatic links
-digests 10-20% protein in the typical meal
What stimulates the release of pepsinogen in the cephalic phase?
Vagus nerve
What stimulates the release of pepsinogen in the gastric phase?
Luminal HCl locally stimulates release
Gastrin and secretin stimulate release
What cells secrete gastric mucus?
Neck cells and surface epithelium
Is gastric mucus acidic or alkalotic?
Alkaline- possess high bicarb level
What stimulates mucus secretion?
PNS (Vagus), gastric distention, and PGs stimulate mucus and bicarb secretion
What increases gastric mixing and emptying?
PNS stimulation, gastric distention, gastrin, and motilin
What decreases gastric mixing and emptying?
-SNS stimulation, secretin, CCK, GIP, H+, digestion products of fats and proteins in the duodenum, and duodenal distention
