Salivary, Gastric & Pancrestic Secretions Flashcards
How is bile concentrated?
By Na/K ATPase pumps on the basolateral surface of gallbladder epithelial cells. This pumps Na from the cell into the interstitium, which draws water with it, concentrating the bile which remains in the gall bladder lumen.
What triggers salivary secretions (salivation)?
It is a reflex response to taste/smell/touch receptors in the mouth and chewing.
Name the X3 salivary glands and their locations.
1) sublingual (under the tongue)
2) submandibular (under the mandible)
3) parotid (between ear and jaw)
Name X3 functions of the saliva.
1) keeps the mouth moist
2) keeps teeth and gums healthy
3) secretes salivary containing amylase which begins chemical breakdown of ingested food
Saliva formation is a X2 stage process.
What tonicity of solution does the 1st stage produce?
Which cells are involved in this process?
The first stage produces an isotonic primary solution.
This is formed by salivary acinar cells (same name as pancreatic acinar cells) using ion pumps.
What tonicity of solution is formed by the second stage of the saliva formation process?
Which structure is responsible for this?
The duct system modifies the primary isotonic solution by reabsorbing the NaCl and secreting K and bicarb via Na/K ATPase pumps. The duct cells, however, are impermeable to water.
The final solution is hypotonic.
What is amylase stored in?
How is amylase released from these?
Zymogen granules.
Exocytosis.
What drives saliva secretion?
NOT hydrostatic pressure!
1) adrenergic transmission (alpha-1 & beta-1)
2) cholinergic transmission
3) NANC transmission (e.g. vasoactive intestinal polypeptide)
What is the osmolarity of bile?
290mmol/L
Same as blood plasma
What is the osmolarity of pancreatic juice?
290mmol/L
Same as blood plasma
What happens to the tonicity of saliva as the flow rate increases?
Why?
It increases (becomes closer to isotonic) as there is less time for NA reabsorption in the duct cells.
What happens to salivary secretion as age increases, and why?
Hyposalivation occurs due to gland atrophy as part of the natural ageing process.
What does stomach secretion contain?
- HCl
- Pepsin (pepsinigen)
What is pepsinogen?
What does pepsin do?
Pepsinogen is the pepsin precursor molecule.
Pepsin initiates protein digestion.
Which cells secrete pepsinogen?
What triggers pepsinogen —> pepsin and what cell is this released from?
The chief cells.
The HCl secreted from parietal cells trigger the formation of pepsin from pepsinogen.
What triggers HCl (from the parietal cells) and Pepsinogen (from chief cells) release?
Gastrin and vagus nerve stimulation
Which cells secrete gastrin?
Where are these cells located?
Where is gastrin secreted into?
G-cells.
In the very bottom of the gastric pits.
Into the blood stream, whereby it travels back to the blood supply supplying the other gastric pit cells.
Which cells of the stomach synthesise and secrete intrinsic factor?
Parietal cells (same as those which secrete HCl).
What does intrinsic factor do?
Combines with vitamin B12 to aid its absorption in the ileum.
There are X3 types of glands in the stomach located beneath the gastric pits.
Which type of glands contain the parietal (HCl secreting) cells?
Where are these glands located in the stomach?
The Oxyntic glands.
In the Fundus and body.
There are X3 types of glands in the stomach located beneath the gastric pits.
Which type of glands contain the G (Gastrin secreting) cells?
Where are these glands located in the stomach?
The pyloric glands.
In the pylorus.
What is the general pH of the stomach?
What is the pH of the stomach gastric lining?
Why is there a difference in the pH? Which cells contribute to this?
Stomach = 2.0
Gastric lining = 7.0
This is due to a secreted mucus/bicarbonate barrier from mucous cells.
What type of pump do parietal cells utilise to create a hydrogen gradient when producing HCl?
Where do the chloride ions come from to form the HCl?
A K/H antiporter on the luminal surface of the cell.
They come from the blood supply to the gland and follow the hydrogen ions via chloride ion channels.
At rest, what is the name of the small, scattered and isolated vesicles of tubes within parietal cells?
Tubovescicles.
What do the tubovescicles form when the parietal cells are activated?
They align to form a network of intracellular canaliculi.
What hormone stimulates HCl secretion from parietal cells?
Gastrin.
What cells/receptors does gastrin bind to in order to begin HCl production?
What other X2 ways can HCl be weakly stimulated?
Gastrin binds to CCK-2 receptors on ECL (enterochromaffin-like) cells which causes a release of histamine.
This histamine binds to H2 receptors on the parietal cells to stimulate HCl secretion.
1) gastrin binding straight onto CCK-2 receptors on parietal cells
2) ach binding to M3 receptors on parietal cells (remember this by linking the NT to the fact that digestion is a parasympathetic activity)
How is HCl production negatively fed back?
The production and therefore presence of HCl in the stomach is detected by D-cells (remember as D for detecting) which produce somatostatin. This signal reaches the G-cells and instructs them to stop producing gastrin. No further HCl is formed as a result.
How does omeprazole work?
What is it used for?
It is a proton pump (H/K ATPase) inhibitor.
It is used to treat gastroesophageal reflux disease (GERD).
Is omeprazole reversible or irreversible?
It is irreversible.
If omeprazole is irreversible, how do we ever produce HCl again and digest food after taking it?
It only blocks about 70% of the pumps, with new parietal cells being regenerated constantly.
What is the name of the class of enzymes that the pancreas releases into the duodenum, which require activation once in situ?
Pro-enzymes.
What class of enzymes in the small intestine activate pancreatic pro-enzymes?
Enterokinases.
What is the concentration of bicarb found in pancreatic juice?
120mmol/L
