Gastric secretion Flashcards
Where is the antrum?
The end of the stomach
Function of the fundus?
Storage
Function of the body of the stomach? What 4 things does it secrete?
Storage
HCL secretion
Pepsinogen secretion
Mucus and Intrinsic factor secretions
Wht does the body of the stomach produce?HCL secretion
Pepsinogen secretion
Mucus and Intrinsic factor secretions
HCL secretion
Pepsinogen secretion
Mucus and Intrinsic factor secretions
Why is pepsinogen released not pepsin?
Because pepsin would degrade the stomach and we wouldn’t have one :(
Function of the antrum?
Grinding and mizxing
Produces gastrin (hormone)
What cells and where is gastrin released? (a hormone)
G Cells in the antrum
What does a gastric pit lead to?
Gastric gland:
-Mucus neck - become/replace the mucus cells in the epithelium (mucus)
-Parietal cells (HCL and intrinsic factor)
-Chief cells (Pepsinogen)
What cells are in a gastric pit and what do they produce?
-Mucus neck - become/replace the mucus cells in the epithelium (mucus)
-Parietal cells (HCL and intrinsic factor)
-Chief cells (Pepsinogen)
What do CO2 and H2O combine to form (in parietal cells)?
H2CO3 (Carbonic acid)
What enzyme speeds up this reaction? (CO2 +H20)
Carbonic anhydrase
Where does this reaction occur?
In the parietal cells
What does carbonc acid separate into?
H+ and bicarbonate (HCO3)
How do the hydrogen ions leave the cell into the stomach?
Through the HK ATPase pump into the lumen of the stomach though the apical membrane
HKAptase aka
Proton potassium pump
Bicarbondate goes wehere/ How? What happens to blood pH after a meal? Ho w does Cl get into stomach lumen?
Bicarbonate goes into the blood through the basolateral membrane (Bicarbonate Chloride pump).
Blood pH increases slightluy because more bicarbonate being pumped into the blood
Cl enters through the bicarbonate/Chloride pump.
What does post prandial mean?
After a meal
Does gastrin travel in the blood?
Yes, it is endocrine
What happens when gastrin attaches to receptor on basolateral membrane of parietal cell?
Stimulates influx of Ca, stimulates protein kinases which increases the activity of the HKATPase pump, leading to more H in Stomach
H2Histamine receptor is where? Coupled up to what? Converts what to what? Which works on what and causes what?
On the basolateral membrane of the parietal cells, coupled with G protein (Gs - G Stimulatary) - Activates AC (Air conditioning jks - Adenylate cyclase). In turn ATP - cAMP. cAMP activates proteikn kinase A - stimulates HKATPase pump. More acidic stomach.
So Gastrin, histamine and ACh (Acytyl Choline) are stimulatory to which ATPase and so then what?
The Potassium Proton pump, which makes stomach more aciidc.
ACH released when? Acts on what? Acts on what?
By stimulation of the parasympathetic nervous system. Acts on M3 (muscarinic recpetor), also leads to an influx of Ca, activates protein kinases and stimulates HKATPase pump.
Wht effect do Prostaglandins do? Essentially inhibitory or stimulatory of the proton pump?
Inhibitory.
Protoglandin - receptor - Gi (G inhibitory protein), inhibit Air Conditioning (AC) and therefore the HKATPase pump
How is gastric acid secretion controlled?
Endocrine (release of gastrin)
Vagal and local reflexes - parasympathetic
Paracrine - histamine
What is the Cephalic phase of stimulation of gastric acid secretion? How does it innervate?
Sight, smell, taste of food -> stimlation of vagus nerve (parasympathetic rest and digest):
-> ACh release
-> stimulation of G cells to release Gastrin
ACh and Gastrin stimulate ECL releasing Histamine
Gastrin, Histamine and ACh act on the Parietal cells to get HCl into the stomach
What is the gastric phase of stimulation?
Presence of food in the lower oesophageal sphincter -> stimulates vagus nerve and enteric reflexes -> ACh
Protein in stomach -> stimulates the relase of gastrin (G Cells)
Gastrin and Histamine both stimulate ECL to relase histamine whihc also acts on Parietal cells
What are the mechanisms inhibiting gastric acid secretion? (Cephalic, Gastric and Intestinal and fat/carbs)
Cephalic - stop eating/thinking/smelling food - reduced vagal activity
Gastrin - negative feedback. Gastrin casues HCl release, as pH drops, there is a reduced gastrin release
Intestinal Phase - Duodenum acid initiates enterogstric (splanchnic reflex). Also sectrets secretin (S Cells in duodenum mucosa, creates bicarbonate secretion which neutralises acid)
Fat/CHO in Duodenum -> GIP (Gastrin Inhibitory Peptide) -> reduced gastrin secretion and reduced parietal HCl secretion
Where is secretin released from? What does it cause?
S cells in duodenum mucosa in response to acid. Causes bicarbonate release which in turn neutralises acid.
WHy do we need to neuralise contents into duodenum
Because otherwise it will denature the enzymes used in digestion. Also will damage the duodenal surface
What are enterogastrones? What causes them to be released?
Hormones released from the glad cells in the duodenal mucosa:
-secretin
-Cholecystokinin (CKK)
-GIP
Released in response to acid, hypertonic solutions, fatty acids or monoglycerides in the duodenum
Which 2 ways do enterogastrones prevent further acid build up in the duodenum?
Inhibit gastric acid secretion
Reduce gsatric emptying (inhibit motility/contract pyloric sphincter)
How does Pepsinogen get converted to pepsin?
Through contact with HCl (in low pH)
Are pepsins inactivated in neutral pH?
Yes (phew! Otherwise they would digest our intestines!)
How is the release of pepsinogen controlled?
Control of Chief cells which is the same as for the parietal cells and releae of HCl;
How is gastric mucous produced?
By surface epithelial cells and mucus neck cells
WHat does gastric mucous do?
Lubricates and protects!
Protects mucosal surface from mechanical injury and maintains neutral pH (high HCO3 content) preventing corrosion and pepsin digestion
What do we get if don’t absrob vit B12?
Pernicious anaemia (failure of erythrocyte maturation)
\What is intrinsic factor produced by?
Parietal cells
