Secretions of the GI & Pancreas Flashcards
Function of the saliva?
What does it do to digest this stuff?
providing the first steps for the digestion of starches and lipids
(done by amylase in the saliva and a lingual lipase)
diluting and buffering particles of the food
lubrication of the ingested food
3 types of salivary glands
Parotid Glands:
biggest ones, composed of serous cells - secrete water, ions, enzymes (rich in amylase)
25% of daily output from parotid
Submaxillary glands (mixed), Sublingual glands (mixed):
- both serous and mucous
- secrete most of the daily output of saliva
aqueous fluid + mucin glycoprotein
75% of daily output
Structure of the salivary glands? (4 parts)
what are each function?
Acinus (blind end) –> composed of aciar cells –> responsible for secreting initial saliva.
myoepithelial cells –> mostly directly outside to the acinus cells in the acinus but can go around the intercalated duct… important for controlling ejection of saliva from the acinus down to the duct through contractions and changing the morphology of the flow.
Intercalated duct –> smaller cells that are extended and go to the striated duct. saliva is going to have a similar composition to that of the plasma at this point (isotonic).. but remember our saliva is usually hypotonic.. this modification happens at the STRIATED DUCT!
Striated Duct lined by columnar cells (ductal cells) –> responsible for producing final saliva
What creates the hypotonic saliva from the isotonic saliva in the intercalated duct?
ductal cells in the striatal duct.
Striated duct?
lined by columnar epithelial cells (ductal cells) –> responsible for producing final saliva.
What is saliva not?
what is it composed of?
not an ultra-filtrate of the plasma
water, electrolytes, alpha amylase, lingual lipase, kvllikrein (important for bradykinin), and mucus.
Saliva is compared to plasma with K, HCO3, Na, Cl
high potassium + bicarbonate (compared to plasma) –> secreted into acinus
low Na and Cl (compared to plasma) –> absorption into blood
Ductal cells do what with Na/Cl and K/HCO3
Na + Cl are shoved out of the saliva at bigger quantities than the absorption of K+ and HCO3 to maintain it!
Na/Cl absorbed (into blood) more than KHCO3 secretion (into acinus)
What’s happening at the lumenal side or the basolateral side of the ductal cell?
On the basolateral side:
1) we have a Na/K ATPase. shoving 3 Na out and 2K in.
2) Cl channels out of the cell
3) HCO3 Na symporters into the ductal cell
on the apical side:
1) Na/H exchangers (Na in, H out)
2) Cl/HCO3 exchanger (Cl out, HCO3 in)
* * also have a chloride channel regulated by cAMP which helps get chloride into the cell or out of the cell (CFTR channel)***
3) H/K exchanger (K in, H out)
How does saliva become hypotonic as it flows through the ducts?
Ductal cells are H2O impermeable.
so we’re not letting water to get into the basolateral side, so we have a lot of water, less solute in the end.
PNS innervation of the salivary glands comes from what?
which one goes to which glands?
facial nerve (CN7) –> submandibular + sublingual
Glossopharyngeal nerves –> to the parotid gland
SNS innervation of salivary glands comes from what?
T1-T3 (sometimes T4) –> superior cervical ganglion –> serves to all 3 glands
what is the main driver of the regulation of the salivary secretions? EXCLUSIVELY
what up regulates the parasympathetic system?
Negative?
ANS (composed of PNS + SNS)
Conditioning (pavlov)
Food
Nausea
Smell
Dehydration
Fear
Sleep
What happens when you up regulate PNS?
stimulates the facial and glossopharyngeal –> ACH binds to muscarinic receptor in the acinar or ductal cells –> increases IP3 and the production of Ca2+ –>
end result = higher saliva production, higher HCO3 and enzyme secretions, contractions of myoepithelial cells
What happens when you upregulate the SNS for salivary glands?
T1-T3 release Norepinephrine –> Beta Adrenergic Receptor (BAR) –> production of cAMP –>
end result = higher saliva production, higher HCO3 and enzyme secretions, contractions of myoepithelial cells
what’s good to know about PNS and SNS with salivary glands? THIS IS IMPORTANT
Parasympathetic and sympathetic are BOTH STIMULATING.. so similar output, but PNS is dominating.
How does ADH and aldosterone modify saliva?
decreasing Na+ concentration and increasing K+ concentration
What does atropine do?
antagonist of muscarinic ACH receptors.
so inhibits saliva production of the PNS. so less Ip3, less Ca2+!
HCl does what? what does it work with?
main goal of acid in the stomach? secondarily?
components of gastric juice?
together with pepsin, initiates protein digestion.
activate pepsinogen to do pepsin
secondarily –> acid kills a ton of bacteria that enter the stomach.
HCl Pepsinogen Mucus Intrinsic Factor H2O
What is pepsinogen?
What is mucus? what does it work with?
What does intrinsic factor do?
what does water do in the gastric juice?
inactive precursor of pepsin
lines the wall of the stomach and protects it from damage, lubricant, and works with HCO3 it helps to neutralize acid and protect the surface to maintaining a neutral pH
glycoprotein and super important for absorption of vitamin B12!
solubilizes much of the material
Oxyntic Gland vs Pyloric gland?
similar?
different cells in each and what do they do?
both similar structures, both have surface mucosal cells. both have enterochromaffin Cells, both have somatostatin (D cells)
different: Oxyntic glands have Parietal Cells (secrete the acid), and Chief cells (secrete pepsinogen), and Enterochromaffin-like Cells (secrete histamine)
Pyloric gland has G cells which secrete Gastrin –> this goes into the blood –> back to the stomach.
What does somatostatin do?
released from D cells inhibits gastric acid release.
Where are oxyntic glands located? Pyloric?
main function?
body + fundus
Antrum
secretes acid (oxyntic) and synthesizes and releases gastrin (Pyloric)
In the stomach, where would you NOT find parietal cells and chief cells?
antrum.
What is the importance of the # of parietal cells?
why do parietal cells have a ton of mitochondria?
where is HCl formed in the parietal cells?
what is the main goal of low gastric pH?
determines the maximal secretion rate.
critical to producing a ton of acid. (stomach has a pH of 1, so a ton of acid is going out).
at the villus like membranes of the canaliculi (little invaginations in the cell)
to convert pepsinogen to pepsin
What’s going on on the luminal side of the parietal cell?
basolateral?
what happens intracellularly?
basolateral:
1) Na/K atpase
2) HCO3/Cl exchanger (HCO3 in, Cl out)
Luminal:
1) H/K ATPase (K+ in, H out)
2) Cl out to lumen (following H to form HCl in the lumen)
the bicarbonate is going to be generated and absorbed and the H is going to be secreted into the lumen to form HCl… all this is made possible by Carbonic Anhydrase!
What happens when we eat?
“alkaline tide”. we have a ton of acid in our stomach so in our blood we’ll have a lot of HCO3 being absorbed into the blood.
What does Omeprazole?
H/K proton pump inhibitor.
Lowers HCL, so helps people with peptic ulcers, acid reflux.
