Gastric Secretion Flashcards
What does the body of the stomach release and produce
Mucus
HCl
Pepsinogen
Intrinsic Factor
Describe the role of the antrum
Secretion of Gastin, and mixing/grinding of food.
Describe the role of the fundus
Storage
Describe the role of mucus in the stomach
Protection of the stomach wall
Describe the role of HCl in the stomach
Maintains acidity, activates pepsin and denatures proteins and bacteria
Describe the role of pepsinogen
Secreted by the stomach wall, proeznyme of pepsin. Cleaved by gastric acid. Pepsin digests proteins.
Describe the role of intrinsic factor
Binds to b12, in order to be absorbed in the small intestine
What are gastric glands? What are their components?
Secrete gastric acid and protective mucous. Contain chief, parietal and mucous neck cells
What do chief cells produce
Pepsinogens
What do parietal cells produce
HCL
Intrinsic Factor
What do mucous neck cells produce?
mucous
Describe the Mechanism of Parietal Cells
H2O and CO2 are broken down into Carbonic Acid (H2CO3) via carbonic anhydrase (unstable compound).
Carbonic Acid breaks down to Bicarbonate (HCO3),and enters into circulation via a HCO3/CL paired transporter. It then follows it’s gradient into the stomach lumen
The H+ ion, enters the stomach lumen via K+/H+ paired transporter.
H+ and CL+ ions moved into stomach lumen (HCL)
Water also moves into the stomach due to the change in osmotic gradient.
What is the typical pH of the blood
pH >7.4
What is the typical pH of the stomach
pH <2
Name the hormones regulating the digestive system
Gastrin Cholecytokinin Secretin Motilin Gastric Inhibitory Peptide
What is the function of gastrin
Stimulation of gastric acid secretion (parietal cells). Increases gastric motility.
What stimulates release of gastrin
Released in presence of peptides and amino acids in the stomach lumen, increased stomach pH
What inhibits gastrin secretion?
Release of somatostatin and decrease of stomach pH.
What releases gastrin?
Gastrin is secreted by G cells into circulation and carried to the gastric fundus and cardia.
where are the majority of parietal cells found
The majority of paritetal cells are found within the cardia and fundus of the stomach
What three mechanisms controlling the secretion of gastric acid
Neurocrine (vagus/local reflexes)
Endocrine (gastrin)
Paracrine (histamine)
Mechanism of Vagus/Local Reflexes on gastric secretion
Acetyl Choline –> increase of intracelluar Ca+, activation of protein kinases, activation of K/H pump
Mechanism of Paracrine on gastric secretion
Histamine - Paracrine, released locally to parietal cells, ATP–> cAMP, activate protein kinases, K/H pump
Mechanism of endocrine system on gastric secretion
Gastrin - Increases intracellular Ca+, activating intracellular kinases, activating the K/H+ pump
What effect does sight, smell and taste have on gastic acid secretion
Stimulation of the Vagus Nerve. This releases ACh and G cells
What effect does the release of gastrin and ACh have on the paracrine system?
In ECL cells, gastrin and ACh secretion stimulate the release of histamine
What are ECL cells
Enterochromaffin-like cell. Neuroendorcrine cells found in the gastric glands that release histamine
What triggers vagal/enteric reflexes in gastric secretion?
Distension of the stomach wall
What is the function of secretin?
Decrease of gastrin and gastric acid secretion
What stimulates release of secretin?
Acid in the duodenum
What triggers and what is the result of enterogastric (splaninc reflex)
When acid is detected in the duodenum, this causes a decrease in gastrin secretion and stimulation of parietal cells.
What are enterogastrones and name three
Enterogastrones are hormones released from the duodenal mucosa.
- Secretin
- Cholecystokinin (CCK)
- GIP
When are enterogastrones released?
In response to acid, hypertonic solutions, fatty acids or monoglycerides in the duodenum, enterogastrones are released
Purpose of enterogastrones
Inhibit gastric acid secretion
Reduce gastric emptying - inhibition of stomach motility & contraction of the pyloric spinchter
Define Zymognen and their purpose in terms of pepsinogen
Inactive precursor. Stops autodigestion. Acidic pH creates the active form of pepsin that hydrolyes proteins.
Neutral pH will denatutre pepsin. Therefore pepsin activation mirrors HCL secretion
What is the role of mucous
Produced by the surface epithelia and mucous neck cells, mucous provdes a protective layer, from acid corrosion, pepsin digestion and mechanical injury
What is the role of intrinsic factor
Required for vitamin b12 absoprtion. B12 forms a complex with intrinsic factor which can be absorbed in the illeum.
Define pernicious anaemia
Those with pernicious anaemia have autoantibodies that attack intrinsic factor rendering them useless.
