Secretions of GI Tract and Pancreas Flashcards
How does the saliva composition compare to plasma?
Saliva is hypotonic compared to plasma
What all is in saliva?
- water
- electrolytes (K+ and HCO3- especially)
- alpha amylase
- lingual lipase
- kallikrein
- mucus
What are the parts of the salivary ducts? (4)
- acinus
- myoepithelial cells
- intercalated duct
- striated duct
What is the acinus?
the blind end that secretes the inital saliva
What do myoepithelial cells do?
Have motile extensions, when stimulated contract to eject saliva into mouth
What does the intercalated duct do?
Is just a channel. Saliva here has composition similar to plasma
What does the striated duct do?
Is lined w/ductal cells that modify comp of saliva by altering electrolyte concentration
What are the pre and post synaptics that are part of the parasympathetics of secretion?
pre - start at CN VII, XI
post - autonomic ganglia innervating individual glands
What increases firing of parasympathetics and thus saliva production? (4)
- food
- nausea
- smells
- conditioning
What decreases firing of parasympathetics (saliva production)? (3)
- dehydration
- fear
- sleep
What are the steps of parasympathetic stimulation? (4)
- stimulus stimulates ANS, sends signal
- Ach released
- ACh attaches to mAchR
- IP3, Calcium increase, leading to saliva
What are the pre and post synaptics that are part of the sympathetics of secretion?
pre - originate at cervical ganglion (T1-T3)
post - extends to glands in periarterial space
What does stimulation of sympathetics lead to, saliva-wise? (3)
- increased saliva production
- increased bicarb and enzyme secretions
- contraction of myoepithelial cells
Which system is saliva under the control of?
the ANS only
What are the main components of gastric juice? (5)
- water
- hydrogen ions (for HCl)
- Pepsinogen
- Mucus
- Intrinsic factor
What does hydrochloric acid do?
Initiates protein digestion by activating pepsinogen to pepsin
kills lots of bacteria that enter the stomach
What is pepsinogen?
The inactive precursor to pepsin
What is the purpose of mucus?
Lines stomach to protect it from gastric acid, lubricates the mucosa, maintains neutral stomach pH, it and HCO3 neutralize acid
What is the purpose of intrinsic factor?
Binds to vitamin B12, is required for its absorption
Where is vitamin B12 absorbed?
Ileum
What is the purpose of water in gastric juice?
- Is medium for HCl and enzyme action
- solubilizes ingested material
Regarding parietal cells:
- what do they secrete?
- Where are they located?
- Parietal cells secrete HCl and Intrinsic factor
- Are located mainly in the body of the stomach
How does HCl get pumped into the stomach lumen?
- Hydrogen ions generated w/in parietal cell from dissociation of water, done by carbonic anhydrase (makes bicarb, hydrogen)
- bicarb transported out of basolateral membrane in exchange for Cl-
- H+ pumped into lumen in exchange for K+ through proton pump
Regarding chief cells:
- what do they secrete?
- where are they located?
- Secrete pepsinogen
- Found in body of stomach
Regarding G cells:
- What do they secrete?
- Where are they located?
- Produce gastrin
- Located in antrum
Regarding Mucus cells:
- What do they secrete?
- Where are they located?
- Secrete mucus, HCO3 and pepsinogen
- Located in the antrum
What is the direct path of gastric secretion?
Vagus nerve → ACh → parietal cells
- vagus stimulation stimulates M3 receptor
- Gq activated
- IP3/Calcium released
- H-K ATPase activated, secretes H+
What is the indirect path of gastric secretion?
Vagus → GRP → G cells
How does gastrin activate parietal cells?
G cells normally inhibited by somatostatin. Gastrin stimulates CCKb receptor: - Gq activated - IP3/Ca2+ released - H-K ATPase activated ALSO ACTIVATES ECL CELLS
How does histamine effect gastric secretions?
Stimulates it by:
- ECL release histamine
- acts on H2 receptor
- Gs activated
- increase in cAMP
- H-K ATPase activated
How does somatostatin effect gastric secretions?
Decreases?
