Lec 20 GI Secretory Function Flashcards
What 3 things in salivary secretion?
- bicarbonate
- salivary amylase
- lingual lipase
is saliva isotonic, hypotonic, or hypertonic?
hypotonic
What happens to salivary bicarbonate concentration as salivary flow increases?
bicarbonate concentration increases
What are the two organs and functions of the stomach?
fundus and body: secretion reservoir
antrum: mixing and grinding
What 3 things are first secreted in stomach when food enters?
- Vagus/parasympathetic secretes acetylcholine
- ECL cells secrete histamine
- G cells secrete gastrin
What 4 things are responsible for turning on parietal and chief cell secretions?
- vagal activity [ACh]
- gastric distension
- gastrin
- histamine
What 2 things do parietal cells secrete?
Acid [H+]
Intrinsic Factor [IF]
What cells secrete gastrin?
G cells in antrum
What do chief cells secrete?
pepsinogen
What are two sources of lipase
lingual –> saliva
gastric: cells in fundus
What cells in glands in proximal stomach vs distal?
proximal: ECL cells, chief cells, parietal cells
distal: G and D cells
both: mucous cells
How many layers of muscle in stomach? What are they?
- circular
- oblique
- longitudinal
What type of action is histamine [hormone, paracrine, autocrine, etc]?
paracrine –> released from ECL cells and activates parietal cells at local level
What are foveolar cells?
mucus secreting cells
what type of cells in mucous neck?
gastric stem cells
In parietal cell – what happens to H+, Cl-, HCO3-, K+?
- K enters cell via Na/K ATPase on basolateral side
- K exits via K channel on lumen and reenters via H/K ATPase that pumps H+ out into lumen
- Positive charge in lumen attracts Cl- that exits cell via Cl channel passively
- HCO3- produced as by-product of acid exits basolateral side into blood stream
What is mech by which parietal cell activated?
- ACh to M3, Histamine to H2, or Gastrin to CCK-B
- at activation, increase cellular Ca [in case of ACh or gastrin] or AMP [via histamine] which causes H/K ATPase to migrate to luminal cell surface
What 2 things activate ECL cell to release histamine?
- Acetylcholine
- Gastrin
How does gastrin act on parietal cell [direct and indirect]?
- activates parietal cell to secrete HCl
- activates ECL to secrete histamine that then induces further HCl secretion by parietal
How does vagus/ACh act on parietal cell [direct and indirect]?
- activates parietal cell to secrete HCl
- activates ECL to secrete histamine that induces further HCl secretion by parietal
How does somatostatin act on parietal cell [direct and indirect]?
- inhibits parietal cell HCl secretion
- inhibits G cell gastrin secretion [main function, paracrine]
- inhibits ECL cell histamine secretion
What activates somatostatin release from D cell?
- HCl produced in proximal stomach travels down to distal stomach where D cell senses the low pH and releases SST
What does D cell secrete?
somatostatin
What is GRP?
- a peptide released by parasympathetic nerves in response to distention
- causes G cell to release gastrin
what happens to gastrin if no acid in stomach
its elevated
what does gastrin do? what does it act on?
- hormone released from G cell
- activates ECL cell to release histamine
- activates chief cell to release pepsinogen
- activates parietal cell to release H
What does distention of stomach do?
- can turn on acid production
what is the functional unit of the pancreas
gland lined by acinar cells
What do pancreatic duct cells secrete?
- release HCO3 into lumen via Cl/HCO3 exchanger
- release Cl via CFTR channel
How does CAMP affect pancreatic duct cell secretion?
- CAMP causes increased Cl secretion via CFTR into lumen
What 3 things in pancreatic duct cell are stimulated by hormone secretin?
- more Cl secreted out to lumen via CFTR
- increased activity Cl/HCO3 exchanger [Cl into cell from lumen, HCO3 out to lumen]
- increased activity NBC [exchanges HCO3 into cell from basolateral side, Na out basolateral to blood stream]
How does pancreatic flow affect pancreatic bicarbonate conc?
- increased pancreatic flow –> increased pancreatic bicarbonate concentration
What causes s cells to produce secretin?
acid coming into lumen
What do pancreatic acinar cells secrete? What 5 things activate their secretion [via what 2 secondary messengers]
- enzymes released from granules into duodenum
release activated by: - GRP, ACh [m3], CCK [CCK] via Ca
- VIP, Secretin via cAMP
PRIMARY TRIGGER = CCK
What are bile acids formed from?
cholesterol
How are primary bile acids formed from cholesterol? where are they secreted? where reabsorbed?
formed: via dehydroxylase and conjugation with glycine/taurine to make them soluble
secreted: into bile
reabsorbed: in terminal ileum
How are secondary bile acids formed from cholesterol? where are they secreted? where reabsorbed?
formed: via dehydroxylase primary bile acids [by bacteria] by bacteria
reabsorbed: by colon, conjugated by liver, secreted back into bile
What are major effects of bile acid conjugation?
- lowers pKa to enhance hydrophilicity [makes more water soluble]
- reduces passive diffusion across cell membranes in transit in biliary tree
Where are conjugated bile acids reabsorbed?
- in terminal ileum
- circulate back to liver via enterohepatic circulation
What are micelles? function?
- bile acids form sphere with hydrophobic part in center, hydrophilic part on outside
- hydrophobic interior allows to package that fats while still staying soluble
- transport lipids for absorption
What are components of human bile?
- 2/3 primary and secondary bile salts
- some phospholipids, cholesterol, protein, bilirubin, electrolytes
Where does fat absorption occur?
jejunum and ileum
What is possible consequence of getting rid of ileum?
- mess up enterohepatic circualtion
- don’t get enough reabsorption of bile salts
- liver can’t make enough to compensate so get bile salt deficiency
What 4 things tell bile duct to make HCO3?
- secretin
- CCK
- gastrin
- vagal stimulation [ACh]
What do VIP/NO do to sphincter of oddi?
- relax sphincter so allow stuff to come through when gall bladder contracted above
What 2 things tell gall bladder to secrete bile salts?
- CCK
- ACh [vagal]
What is responsible for vagal afferent signal to tell vagus to induce bile salt secretion?
CCK
