3. Secretory processes control systems which regulate motility secretion and secretion Flashcards
List the 5 components of gastric secretions in the stomach and their functions
- Hydrogen ions - produced by parietal cells - converts pepsinogen into pepsin
- Pepsin - produced by chief cells as pepsinogen - breaks down protein
- Intrinsic factor - forms a complex with vitamin B12 for absorption in terminal ileum
- Mucus - lubrication and protection of mucosa from being digested by pepsin
- Water
Describe the 2 functions of gastric acid.
- Converts inactive pepsinogen into the active enzyme pepsin
- Kills a large number of bacteria that enter the stomach
What is the pH of blood?
7.4
What pH level can the stomach reach with high rates of gastric acid secretions?
Approx pH 1
Why do parietal cells expend a lot of energy?
Because they produce HCl which requires a lot of energy - parietal cells would therefore have lots of mitochondria
Where are oxyntic glands found?
In the fundus of the stomach
What cells are found in oxyntic glands?
(Lumen) Epithelial cells Parietal cells Chief cells (Muscularis mucosae)
By what mechanism is hydrogen actively “pumped” into the gastric lumen?
H+, K+ -ATPase
What catalyses the production of bicarbonate from OH- and CO2 in parietal cells to then enter the bloodstream?
Carbonic anhydrase (CA)
What are the 3 stimulants for acid secretion and what receptors do they act on (parietal cells)?
- Gastrin - CCK2-R (cholecystokinin-2)
- Histamine -H2
- Acetylcholine - Ach-R (parasympathetic neurotransmitter of vagus nerve)
What cells produce histamine and where can they be found?
Enterochromaffin-like cells (ECL cells)
Found near parietal cells
Outline the cephalic phase in gastric secretion.
1st phase
Starts with the sight, smell, taste of food
Vagus nerve activates parietal and gastrin cells
Leads to moderate stimulation of HCl/pepsinogen release
Outline the gastric phase of secretion
2nd phase
Caused by proteins in antrum/distention of stomach
Vaso-vagal reflex & gastrin (& histamine)
Strong stimulation of HCl/pepsinogen
What foods directly stimulate gastrin release?
Coffee
Protein/peptides
Calcium rich foods
(Alcohol DOES NOT affect release)
Outline the intestinal phase
3rd phase
Proteins entering duodenum -> gastrin release (excitatory)
HCl in duodenum -> secretin release (inhibitory)
Lipids in duodenum -> peptide YY (inhibitory)
What 3 things are secreted by the crypts of the small intestine and what are their functions?
- NaCl/ NaHCO3 - neutralises gastric pH
- Amylase - starch digestion
- Enteropeptidase - activates trypsinogen
What are found on villus tips of the small intestine to aid digestion?
Brush border enzymes
What interventions can be used to reduce gastric secretions by targeting histamine release?
Antihistamines
Cimetidine
What are generally used to reduce gastric acid secretions?
List 3 examples.
Proton pump inhibitors (PPIs)
Omeprazole, lansoprazole, esomeprazole
Gastric acid plays a role in fighting bacteria. What does the use of PPIs put the patient at higher risk of?
Nosocomial infections (originate in hospitals) e.g. Clostridium difficile
When is gastric acid secretion at its peak?
1 hour post-ingestion
At what pH is gastrin inhibited?
pH < 3
What inhibitory hormone is released in response to low pH?
Somatostatin
What are the 3 enterogastrones (hormones) released by the duodenum in response to low pH?
- CCK
- Gastric inhibitory polypeptide (GIP)
- Secretin
What is secreted by the pancreatic duct and what causes its release?
Bicarbonate
Release from duct cells stimulated by secretin release, which is stimulated by HCl in the duodenum
What are released by the acinar cells of the pancreas and what stimulates their release?
Pro-enzymes. Their release is stimulated by CCK which is released in the presence of proteins/lipids.
NaCl also released
