Gastric Secreation Flashcards
What is the overall function of the fundus and what property allows this
Storage
Thin and stretchy
Other than Storage what is the further function of the Body of the stomach
Production of: Mucus HCL Pepsinogen Intrinsic factor
What produces mucus in the stomach
Epithelial cellls and mucus neck cells
How does the mucus in the stomach have a cytoprotective role
Mucus produces a high content of bicarbonate which mops up the Acid creating a neutral pH region on stomach lining
So stops acid corrosion of stomach lining
as well pepsin become inactive due to neutral pH so further protect from pepsin digestion on stomach lining
What is the purpose of pepsinogen in the stomach
Inactive from of pepsin, to protect the stomach lining from being digested
How does the oesophagus lining differ from the stomach
Doesn’t have mucus layer to protect from acidic conditions
What does parietal cells produce
HCL
Intrinsic Factor
What produces pepsinogens
Chief cells
What is the three type of cells that compose the gastric glands
Mucus neck cells
Chief cells
Parietal cells
Why is the production of intrinsic factor the only essential function of the stomach
As is the only non compensated function
What is the intrinsic factor required for
Vitamin B12 Absorption at the Ileum
What is the functions of the Antrum of the stomach
Mixing and Grinding of stomach (due to thick muscle)
Secretion of gastrin hormon e
When is pepsinogen converted to inactive form
When HCL production increases therefore lowering pH to below pH 3
What does the production of pepsin further convert
Further pepsingen to active form pepsin
How is HCL formed from parietal cells
The diffusion of CO2 from the blood combing with water to form carbonic acid which dissociates to hydrogen and bicarbonate
Hydrogen pumped into the stomach lumen in exchange for potassium
Bicarbonate exchanged into the blood in exchange for chloride
Chloride cross parietal cell through chloride channel
The combines with hydrogen in the stomach lumen to form HCL
How does the presence of HCL affect the pH in the stomach
Decreases to pH 2
How does the presence of Bicarbonate affect the pH of the blood
Slight increase to pH 7.4
What catalyses the formation of carbonic acids in the parietal cell (CO2 + H2O)
Carbonic anhydrase
What are the three hormones that increase HCL secretion in the parietal cells
Gastrin
Achetlycholine
Histamine
How does Gastrin hormone and acetylcholine increase the production of Acid
Gastrin travels in the blood to the stomach and ACH works on chollingeric receptors,
and both binds to G protein couple receptor that increases calcium level
combining to protein kinase allowing hydrogen out of the parietal cell to form HCL
What is used in exchange of hydrogen from the protein pump on the parietal cell
Potassium is exchanged into the parietal cell
How does histamine cause an increase on acid production
acts on G protein couple receptor to trigger the production of cAMP that combined with protein kinase C protein pump
releasing hydrogen to outside the parietal cell
How does prostaglandin decrease HCL production in parietal cells
Couples up to inhibitory GI protein preventing the formation of cAMP therefore reducing the function of protein kinase protein pump, so hydrogen is not exchanged out of parietal cell
Gastric secretion is controlled by what three mechanisms
Neurocrine (vagus nerve- ACH, local reflex)
Endocrine (gastrin)
paracrine (histamine)
What initiated the cephalic phase
Before eating; The site, smell and taste of food,
Getting the body ready to eat, by preparing acid production in your stomach
What is the first step in the cephalic phase
Increases parasympathetic intervention though vagus nerve
What is the affect of increased vagus nerve intervention
Acts on G cells, releasing hormone Gastrin that acts on parietal cells
as well parasympathetic intervention triggers release of ACH which acts on parietal cells
Both gastrin and ACH then act on ECL cells to release histamine acting on parietal cells
What is the importance of producing acid before you start easting
So food can be sterilised upon entry
what are the three things that occur during gastric phase
Distension of stomach triggers Vagal enteric refelxes, releasing ACH onto parietal cells
Proteins in the stomach activate G cells producing gastrin to act on parietal cells
The production of gastrin and ACH then stimulates ECL cells releasing histamine that acts on parietal cells
What cells does Gastrin and ACH act upon to release histamine
ECL
What cells produce Gastrin
G cells
What triggers the release of Gastrin hormone
Proteins in the stomach ad increased vagus nerve activity
How do you inhibit cephalic phase
Stop eating will decrease vagal activity
How does Gastric phase decrease gastrin production
Due to negative feedback as pH decreases (due to increase in HCL) triggers decrease in gastrin stimulation
What happens in the intestinal phase when acid is present in duodenum
When acid is present in the duodenum causes a enterogastric reflex releases secretin hormone
which both decreases gastrin secretion and gastric stimulation of parietal cells
What is the function of secretin
Stimulates secretion of bicarbonate that indirectly neutralises acid
and inhibits the release of gastrin or HCL from parietal cells
What happens in the intestinal phase when fat is present in duodenum
triggers the release of gastric inhibitory peptide (GIP)
that reduces gastric secretion
and decreases parietal HCL secretion
Name the 3 Enterogastrones
Hormones released from gland cells in duodenal mucosa
Secretin
Cholecystokinin
Gastric inhibitory peptide
What two things triggers intestinal phase
Acid in duodenum
or fat in duodenum
What are enterogastrones released in response to
Acid, hypertonic soln, monoglycerides and fatty acids in duodenum
What are the enterogastrones strategies to reduce gastric emptying
Inhibit motility
or contract pyloric spinchter
What is the overall functions of enterogastrogens
reduce gastric emptying time
Inhibit gastric secretion
