Salivary and Gastric Acid Secretions Flashcards
Although not required, mastication is important for
mechanical breakdown, SA for saliva, easier swallowing
Saliva Function
lubrication, dissolving food for taste, heath of gums, R protein for Vit B12 absorption, amylase and ptyalin for carb digestion, HCO3 for H+ neutralization
3 salivary glands
parotid, submandibular, and sublingual
What types of cells are in salivary glands
acinar and ductal
Acinar cell secretions
isotonic electrolyte (Na, Cl, K, HCO3, H2O), active amylase, mucins, tight junctions permeable to water (SECRETION IS ISOTONIC)
Ductal cells
reabsorbs Na, HCO3 exchanges for luminal Cl, tight junctions impermeable to water
Which salivary gland cells have tight junctions impermeable to water?
ductal
Aldosterone effects salivary gland cells by
increasing the absorption of Na by ductal cells, doesn’t effect rate of salivary secretion
What regulates rate and volume of salivary secretion?
sympathetic and parasympathetic innervation
Final salivary secretion is ________ in comparison to plasma. (hypo- iso- hyper- tonic)
HYPOtonic
PNS and SNS activity cause
INCREASED salivation, intitiated by taste, smell, tactile stimuli in mouth
PNS increases release of what type of saliva
watery
SNS increased release of what type of saliva
proteins and maintains high blood flow to gland by releasing nonadrenergic vasodilators
Increased rate of salivation
by PNS during nausea and vomiting
Decreased rate of salivation
by inhibition of PNS by fatigue, sleep, fear, dehydration
What electrolyte is high at all salivary flow rates
HCO3
At the slowest salivary flow rate…
ductal cells reabsorb most Na and exchange most Cl for HCO3, therefore Na and Cl are low, and K is high
At the fastest salivary flow rate…
ductal cells reabsorb little Na, therefore highest concentration of Na and lowest K
During maximal PNS stimulation would the Na concentration of the saliva be high or low?
HIGH, fast salivation flow rate, low Na reabsorption by ductal cells
Gastric secretions have 3 main functions
Digestion, modulate HCl secretion, and protect lining of gut
Gastric substances that aid in digestion
HCl (parietal cells), Intrinsic Factor (parietal cells), Gastric lipase (chief cells), and pepsinogen (chief cells)
Gastric substances that modulate HCl secretion
Gastrin (G cells), Histamine (ECL cells), Somatostatin (D cells)
Gastric substances that protect the stomach lining
Mucus and HCO3 (surface mucous cells and mucous neck cells)
Secretory cells present in cardiac glands
surface mucous cells and mucous neck cells - mucus and HCO3
Secretory cells present in gastric (oxyntic) glands
surface mucous cells and mucous neck cells - mucus and HCO3, parietal, chief, D cells, ECL
Secretory cells present in pyloric glands
surface mucous cells and mucous neck cells - mucus and HCO3, G and D cells
HCl secretion by parietal cells - H+ production
Carbonic Anhydrase: CO2 + H2O –> H+ + HCO3
HCl secretion by parietal cells - Apical Membrane
H+/K+ ATPase pump: pumps H+ into lumen and K+ into cell
HCl secretion by parietal cells - Basolateral membrane
Excess HCO3 is transported across in exchange for Cl-, HCO3 enters blood and CL- diffuses into lumen to generate HCl
HCl secretion by parietal cells - H2O
passive diffusion with HCl into lumen
Rate limting step of HCl secretion by parietal cells
ATP availability for the proton pump
Alkaline tide
refers to the excess HCO3 entering the gastric venous blood, increasing the pH
factors that increase HCl secretion act synergistically
Gastrin (Ca2+), Histamine (H2 receptors - cAMP), ACh-muscarinic activation (PNS - Ca2+)
Location of receptors for modulation of HCl secretion
basolateral membrane of parietal cell
factors that decrease HCl secretion
Somatostatin (D cells - cAMP), Prostaglandin (cAMP), Secretin (S cells) (decrease cAMP)
What is more effective in reducing H+ secretion, proton pump inhibitor or H2 receptor antagonist?
Proton pump inhibitor
Gastrin Function
increases secretion of HCl, pepsinogen, IF, and Histamine
increases phasic contractions, gastric emptying, and colonic motility (mass movements), trophic - stimulates growth of gastric mucosa
What factors increase Gastrin secretion
GRP (IPANs), ACh, peptides in gastric lumen, secretin, gastric distention
What factors decrease Gastrin secretion
Somatostatin (when pH drops below 3)
Histamine Function
Increase HCl and IF, decrease somatostatin
What factors increase histamine secretion
gastrin
what factor decrease histamine secretion
somatostatin
Somatostatins function
inhibits HCl, gastrin, pepsinogen, IF, histamine secretion; reduces local blood flow by constriction of vessels
What factors increase somatostatin secretion
Low pH (<3), secretin
What factors decrease somatostatin secretion
High pH, ACh, Histamine
Why does vagal stimulation inhibit somatostatin?
to maximize HCl secretion for a acidic lumen (optimize enzymes)
Vagal Stimulation causes release of ACh from enteric neurons which binds
Muscarinic receptors
ACh directly increases secretion of
HCl and gastrin (GRP)
ACh directly decreases secretion of
Somatostatin
Gastrin directly increased release of
Histamine and HCl
Histamine directly activates H2 receptors and increases the secretion of
HCl
Histamine directly activates H3 receptors and decreases the secretion of
Somatostatin
Other factors that increase PNS activity
distention of stomach, protein products in lumen, pH > 3
Other factors that inhibit HCl secretion
duodenal feedback (pH <3, distention of duodenum, high osmolarity in duodenum)
Acidic chyme in duodenum causes
Secretin release from S cells, which inhibits HCl secretion and increases somatostatin secretion
Hyperosmotic chyme and duodenal distention causes
HCl inhibition via short and long neural reflexes
