Secretions of GI Tract and Pancreas Flashcards
Saliva is produced by what?
Salivary glands - parotid, submandibular and sublingual
What glands secrete the most saliva?
Submandibular and sublingual
Describe the salivary gland structure
Acinar cells with myoepithelial cells surrounding
- Connected to intercalated duct
- Connected to striated duct
- Connected to excretory duct
The acinar cells secrete an _____ solution
isotonic
What type of cells contract to help eject saliva from the gland?
Myoepithelial cells
What part of the salivary gland and what type of cells modify the initial saliva?
The striated duct and its ductal cells
The striated duct creates a _____ solution
hypotonic
Striated ductal cells are ______ to water
IMPERMEABLE = helps to create the hypotonic solution
Describe the electrolyte concentrations in the hypotonic saliva
INCREASED K+ and HCO3-
DECREASED Na+ and Cl-
The striated ductal cells _______ more Na+ and Cl-
Absorb
The striated ductal cells _____ less K+ and HCO3- into the lumen
Secrete
Describe the net absorption of the salivary ductal cells
The cells absorb MORE Na+ and Cl- than they secrete of K+ and HCO3-
What controls the salivary secretions?
Autonomic Nervous System (ANS)
Why is the control of salivary secretions unusual?
The parasympathetic system and the sympathetic system BOTH ACTIVATE the salivary secretions (normally oppose eachothers actions)
Parasympathetic or sympathetic.. which one dominates salivary secretion control?
Parasympathetics
What stimuli activates the Parasympathetics to increase saliva secretions?
Conditioning
Food, smell
Nausea
What stimuli inhibits the Parasympathetics to decrease saliva secretions?
Dehydration
Sleep, fear
CN ___ and ___ activate release of ____ to acinar or ductal cells in the salivary glands (parasymp.)
CN 7 and 9 activate release of Ach
Sympathetics T1-T3 activate release of ____ to acinar or ductal cells in the salivary glands
NE
What inhibits the parasympathetic release of Ach to the acinar or ductal cells in the salivary glands?
Atropine
What are the cells in the body of the stomach that secrete components of gastric juice?
Parietal cells
Chief cells
What do parietal cells release in the stomach?
HCl and Intrinsic factor
Why is it important for the parietal cells to release HCl?
Creates a very acidic environment which is required for pepsinogen to be converted to pepsin
Why is it important for the parietal cells to release Intrinsic factor?
For the absorption of Vitamin B12
What do chief cells release in the stomach?
Pepsinogen
What are the cells in the antrum of the stomach that secrete components of gastric juice?
G cells
Mucous cells
What do G cells release into circulation from the stomach?
Gastrin
What is secreted and absorbed from a parietal cell in the stomach?
Secreted = H+ and Cl- Absorbed = HCO3-
What can inhibit the secretion of H+ from parietal cells?
Omeprazole
Agents that can stimulate H+ secretion from gastric parietal cells
Vagus - ACh
G cells - Gastrin
ECL cells - Histamine
Agents that can inhibit H+ secretion from gastric parietal cells
Somatostatin
Prostaglandins
What are the 2 ways the Vagus nerve can stimulate H+ secretion from gastric parietal cells?
- Direct - release Ach to parietal cells
2. Indirect - release GRP to G cells, which then release Gastrin into circulation, which then activates parietal cells
Somatostatin can inhibit G cells from releasing Gastrin. When the pH falls to low (too much H+ secretion from parietal cells), what will activate somatostatin to inhibit them more?
Gastrin itself! (negative feedback)
Atropine can block which vagus nerve pathway for stimulation of H+ secretion from parietal cells?
The direct pathway because it releases ACh
– The indirect pathway releases GRP which cannot be inhibited by Atropine
What are the 3 phases of Gastric HCl secretion?
Cephalic phase
Gastric phase
Intestinal phase
What can abolish the cephalic phase of gastric HCl secretion?
Vagotomy
Which phase of gastric HCl secretion accounts for the majority of secretion control?
Gastric phase
What drink can stimulate Gastric HCl secretion?
Coffee
What can inhibit H+ secretion from parietal cells?
Omeprazole
What can inhibit ECL cells from releasing Histamine (Histamine normally activates H+ secretion)?
Cimetidine
What stimulation is the most important stimulus for pepsinogen secretion?
Vagus nerve
H+ triggers local _____ reactions to stimulate chief cells to release _____
Cholinergic
Pepsinogen
What converts more pepsinogen to pepsin?
Pepsin
What does pepsin do?
Degrades food proteins into peptides
Parietal cells also release intrinsic factor. What is it required for and where does this take place?
Vitamin B12 absorption in the distal ileum
Pernicious anemia
Stomach does NOT produce enough intrinsic factor = decreased vitamin B12 absorption
Common causes/disruptions of pernicious anemia/absorption of B12
Causes: atrophic gastritis or autoimmune
- loss of parietal cells or immune attacking IF/parietal
Disruptions: Gastrectomy or Gastric bypass
What makes up the mucosal barrier that protects the gastric epithelium?
Mucous + HCO3-
What will damage the mucosal barrier that normally protects the gastric epithelium?
Acid, pepsin, NSAIDs, helicobacter pylori, alcohol, bile, stress
What is the purpose of the mucosal barrier in the stomach?
To protect the gastric epithelium from HCl and pepsin
Zollinger - Ellison Syndrome
Large secretion of gastrin by duodenal/pancreatic tumors (gastrinomas)
Zollinger - Ellison Syndrome causes an _____ in H+ and Gastrin secretion
INCREASE
How do you diagnose a gastinoma/Zollinger - Ellison Syndrome?
Secretin stimulation test
Under normal conditions, secretin will do what to gastrin release?
INHIBIT
With gastrinomas, secretin will do what to gastrin release?
Cause an INCREASE = ACTIVATE
What are the 2 types of peptic ulcers?
Gastric ulcer
Duodenal ulcer
What is a main cause of a peptic ulcer?
Helicobacter pylori or NSAIDs
A peptic ulcer results in the loss of?
Mucosal barrier loss with excessive acid and pepsin
Gastric ulcer levels of H+ and gastrin
DECREASED H+ and increased gastrin
Duodenal ulcer levels of H+ and gastrin
INCREASED H+ and gastrin
Zollinger - Ellison syndrome levels of H+ and gastrin
MAJORLY INCREASED H+ and gastrin
2 main things the pancreatic juice contains?
HCO3- aqueous solution
Enzymes
What is the purpose of the pancreas secreting HCO3-?
Neutralize the H+ acid from stomach
What do pancreatic enzymes do?
Digest food
_____ activity increases pancreatic secretions
Parasympathetic
______ activity decreases pancreatic secretions
Sympathetic
What cells in the pancreatic duct synthesize and secrete enzymes?
Acinar cells
What cells in the pancreatic duct secrete HCO3- solution?
Centroacinar and ductal cells
Pancreatic acinar cells can secrete enzymes in their active or inactive form. What is an example of enzymes they secrete in the inactive form?
Proteases
For a pancreatic ductal cell, it secretes and absorbs what?
Secretes HCO3- and absorbs H+
Cystic fibrosis associated with a mutation of what?
CFTR Cl- channel in the pancreatic ductal cell
Cystic fibrosis mutation of the pancreas leads to what?
Impaired HCO3- secretion from ductal cells
What are the pancreatic secretion phases?
Cephalic - enzyme secretion
Gastric - enzyme secretion
Intestinal - enzyme AND HCO3- secretion
What molecule activates the release of pancreatic enzymes?
CCK
What molecule activates the secretion of HCO3- from the pancreas?
Secretin