130-131. Secretions of Salivary, Stomach, Exocrine Pancreas Flashcards
What is the Enteric Nervous System? What are the functions of its two plexuses?
What are the functions of the parts of ANS?
What are the 3 modes of GI communication?
ENS: sensory n, interneurons, motor neurons in GI tract (modulated by brainstem), can do patterned motor activity
Myenteric (Auerbach’s) Plexus: b/w smooth muscle layers (longitudinal, circular), peristalsis/GI motility
Submucosal (Meissner’s) Plexus: submucosal, gland secretion, MM innervation
ANS: parasymp = Excitatory (absorption, secretion, motility); symp = inhibitory (acts on blood vessels - 3 ganglion - celiac g, SMG, IMG)
GI comms:
- Endocrine (hormone from cell to blood for effects at great distance)
- Paracrine/Autocrine (diffuses to immediate vicinity
- Neurocrine (nerve innervates specific tissue with synapse)
What are the 4 phases of GI activity
- Cephalic: head, sight/smell/sound/thought food
- Gastric: food in stomach
- Intestinal: food in intestine
- Interdigestive: in b/w meals, stomach/small intestine are empty
What are the 3 main salivary glands, what kind of fluid does each one secrete, and how are they innervated?
- Parotid Gland: serous fluid
- Submandibular: serous + mucous secreting
- Sublingual: serous + mucous secretine
Innervation: Exclusively ANS (cholinergic inputs)
Parasymp = high volume secretion of saliva, VD (CN7, CN9 synapse to CN5)
Symp = low volume secretion of saliva, independent VC (T1 spinal nerves - superior cervical ganglion - follow blood supply to glands)
What are the three key components of salivary glands?
- Acinus: produce ultrafiltrate like fluid
- Intercalated Duct: for saliva transport
- Striated Duct: modify secretion compositions
What is the molecular basis of salivary acini function?
What is composed of in saliva from acini secretions?
What is the effect of ANS stim?
mLc: Driver = Na/K ATPase basolateral (Na out)
Effect = basolateral H/Na exchanger and NKCC cotransport
H/Na exchange: high H efflux = bicarb buildup in cell = bicarb SECRETED apical channel
NKCC: high K and Cl secretions through apical channels
Saliva: high bicarb, Cl, K (not considered plasma ultrafiltrate because requires ATP)
alpha amylase: secreted from vesicles, digests starch - breaks interior alpha 1,4 bonds (not essential, inactivated by stomach acid)
Cells: contractile myoepithelial cells: ANS activation to squeeze fluid into duct
What is the molecular basis of salivary striated duct secretions and function?
How does salivary composition change?
What is the effect of ANS Stim?
Ducts: modify secretion composition, tight junctions limit water movement
Driver = Na/K ATPase basolateral (drives Na removal from saliva, K secretion to saliva)
Effect = H/Na exchanger basolateral
(more bicarb in cell = bicarb secretion via bicarb/Cl exchanger apical)
Composition: More bicarb, less Cl in saliva; less Na, more K
ANS stim via m3AChR: high intracell Ca activates Cl/bicarb exchanger = increased bicarb secretion to saliva
How does salivary composition vary with fluid flow?
How does salivary tonicity compare to plasma?
Low Flow: more time for striated duct modification: MORE hypotonic (LESS Na/Cl/H2O, more K, more bicarb)
High Flow: less time to reduce Na from secretion: LESS hypotonic (more Na, less K, more Cl)
All salivary gland secretions are hypotonic with respect to plasma
List the cells and their functions within the stomach oxyntic glands. Where are oxyntic glands located?
Superficial epithelial cell = produce plasma-like fluid
Mucous neck cell
Stem/Regenerative Cell
Parietal Cell: Acid secreting
Chief Cell: secretes pepsinogen
ECF cell: secretes histamine (paracrine signal)
D cell: somatostatin secreting
Describe the molecular mechanics of parietal cells. What is the function of the acid they secrete?
Proton pumps in tubulovesicles = when stimulated, fuse together to increase surface area of proton pumps = increase gastric acid secretion
Proton pump: H/K ATPase (K in, H out)
key: H2O hydrolyzed to H+/-OH in cell: H+ pumped out, OH- moved to interstitium as bicarb (via CA)
Cl- secretted via passive channel
Acid fx: anti-microbial (protection), activates pepsin from pepsinogen, good pH for pepsin function, denatures peptides (easier for pepsin to work)
How is acid secretion regulated?
- direct path
- indirect path
- pathways in parietal cell
- inhibitory control
Direct: ACh, Gastrin, Histamine stim parietal cell
Indirect: ACh, Gastrin stim ECF cell = histamine release = stim parietal cell
Parietal Cell: ACh/Gastrin act thru Adenylyl cyclase and increase cAMP; Histamine increases intracell Ca (both act synergistically to increase H+)
SST: from D Cells, inhibits ECL cells (lower histamine) and inhibits parietal cells (lower H secretion)
Stretch = drives acid/pepsinogen secretion via vagal-vagal loops or local loops
What stimulates pepsinogen release?
How is pepsinogen activated?
How does gastric acid composition vary by flow rate?
stim pepsinogen release by ACh, Gastrin, Histamine
Activated to pepsin by low pH and pepsin (positive feedback)
High flow: secretion mainly from parietal cells (high H/Cl, low Na, low K)
Low flow: secretion mainly from surface epithelial cells (high Na/Cl, low H, Low K)
What is the function of the gastric mucosal barrier? What cells are protective?
What happens with damage to the mucosal barrier?
Fx: prevent stomach from digesting itself
Mucus gel: layer of insoluble mucus - traps alkaline fluid underneath (neutralizes escaped acid to protect from damage)
Surface mucus cells produce isotonic fluid with bicarb, and secrete bicarb to interstitial space to protect bloodstream
Damage: irritate bloodstream = mast cell activation = histamine release = increase acid secretion (bad positive feedback)
What are the cells in the pyloric region?
Not acid secreting, but stimulate parietal cells for acid secretion
G Cells: secrete gastrin
D Cells: secrete STT
How does the tonicity of exocrine pancreas secretions compare to blood?
How does pancreas composition vary as a function of flow?
ALL secretions are ISOTONIC (pancreatic acinar cells - enzymes; duct cells - high bicarb)
High flow: more bicarb secretion, low bicarb net secretion due to high bicarb stimuli
What is the molecular mechanism for secretions in pancreatic acini and duct cells?
Acini: vesicle enzyme secretion of alpha-amylase (carbs), lipase (fats), proteolytic enzymes (proteins) - stored inactivated in zymogen granules (activated by enzymes on epithelial brush border of cells in intestinal lumen)
Ducts: Driver = Na/K ATPase basolateral
Effect: basolateral Na/H exchanger (H out of cell, high bicarb, bicarb secreted via Cl/bicarb exchanger)
higher flow = more active Na/K ATPase = more active Cl/bicarb exchange
