30 Questions
What is the main function of HCl secreted by the gastric parietal cells?
To activate pepsinogen into pepsin
What is the primary role of the mucus coating over the gastric mucosa?
Both a and b
Which of the following is NOT a function of HCl secreted by gastric parietal cells?
Stimulating the secretion of gastric juice
What is the purpose of the tight junctions between the gastric mucosal cells?
To prevent HCl from penetrating between the cells
Which of the following is the main function of the HCO3- -rich mucus?
To neutralize acid in the vicinity of the mucosa
Where is pepsinogen, the inactive precursor to pepsin, secreted from?
Gastric chief cells and mucous cells
What is the main stimulus for fluid and electrolyte secretion in salivary glands?
Parasympathetic innervation
What is the composition of saliva compared to plasma at all flow rates?
Hypotonic
Where is the primary secretion of saliva produced?
In the acinar cell
What ions are absorbed by the duct cells in the salivary glands?
Na+ and Cl-
Which system controls the regulation of salivary secretion?
Nervous system
What is the true statement about fluid secretion in salivary glands?
An active process involving electrolyte transport
What is the role of basic PRPs and histatins in toxin binding?
Preventing the uptake of tannins by intestinal epithelial cells
How does buffering in saliva help counteract the effects of microbial acids?
Forming H2O and CO2 in the presence of H+
Which proteins in saliva function by attacking microbial cell walls?
Lysozyme and peroxidase
How do urea and ammonia help neutralize acids according to the text?
By forming H2O and CO2
Which component plays a role in preventing microorganisms from binding to oral tissues?
Salivary agglutinin (gp340)
What is the role of carbonic anhydrase in saliva according to the text?
Forming H2O and CO2 in the presence of H+
What is the second messenger pathway associated with binding of acetylcholine to muscarinic receptors?
IP3-Ca2+
What effect does the increase in cytoplasmic Ca2+ have on the secretory cells?
It draws intracellular Cl- into the lumen.
How is water pulled into the lumen during active fluid secretion?
Via aquaporins in the secretory cell membranes.
What process is responsible for the secretion of proteins and glycoproteins in the salivary glands?
Exocytosis
Which neurotransmitter binds to G-protein coupled β-adrenergic receptors to activate cAMP second messenger in serous cells?
Norepinephrine
How is the transient intracellular acidification caused by HCO3- efflux recovered during high salivary flow rates?
By up-regulating activity of basolateral Na+/H+ exchanger
What type of solution is actively secreted by the duct cells in the pancreas?
Alkaline solution
Which enzyme activates trypsinogen to its active form, trypsin, in the duodenal lumen?
Enteropeptidase
Why must trypsinogen remain inactive within the pancreas?
To prevent proteolytic activity on pancreatic cells
What is the function of trypsin inhibitor within the pancreas?
Inhibit trypsin's activity within the pancreas
Which enzymes are activated by trypsin within the duodenal lumen?
Chymotrypsinogen and procarboxypeptidase
What role does enteropeptidase play in pancreatic secretion?
Activates trypsin to trypsinogen
Study Notes
Gastric Parietal Cells and HCl Secretion
- Gastric parietal cells result in net secretion of HCl and net absorption of HCO3−.
- HCl activates pepsinogen to pepsin and provides an acidic environment optimal for pepsin action.
- HCl breaks down connective tissue and muscle fibers, reduces large food particles, and denatures proteins.
- HCl, along with salivary lysozyme, kills most microorganisms ingested with food.
Gastric Mucosal Barrier
- The luminal membranes of gastric mucosal cells are impermeable to H+.
- Tight junctions between cells prevent HCl penetration.
- A mucus coating over the gastric mucosa serves as a physical barrier to acid penetration.
- HCO3–rich mucus also serves as a chemical barrier that neutralizes acid in the vicinity of the mucosa.
Pepsinogen Secretion
- Pepsinogen, the inactive precursor to pepsin, is secreted by chief cells and mucous cells in the oxyntic glands.
Salivary Secretion
- Saliva is hypotonic to plasma at all flow rates.
- [HCO3-] in saliva exceeds that in plasma except at very low flow rates.
- The primary secretion is produced in the acinar cell.
- Duct cells absorb Na+ and Cl- and secrete K+ and HCO3-.
- The parasympathetic innervation provides the main stimulus for fluid and electrolyte secretion.
Regulation of Salivary Secretion
- Acetylcholine binds to G-protein coupled muscarinic receptors with IP3-Ca2+ second messenger pathway.
- Norepinephrine binds to G-protein coupled β-adrenergic receptors, activating cAMP second messenger pathway leading to exocytosis in serous cells.
Functions of Saliva
- Salivary HCO3- and carbonic anhydrase play important roles in counteracting the effects of microbial acids on tooth enamel and dentin.
- Saliva contains proteins that function in regulating the oral microbial flora.
- Proteins like lysozyme, peroxidase, mucins, and salivary agglutinin bind to and aggregate microorganisms, preventing them from binding to oral tissues.
Pancreatic Secretion
- Pancreatic juice consists of pancreatic enzymes actively secreted by acinar cells and an aqueous alkaline solution actively secreted by duct cells.
- The aqueous alkaline component is rich in sodium bicarbonate (NaHCO3).
- Trypsinogen, chymotrypsinogen, and procarboxypeptidase are activated by enteropeptidase and trypsin to their active forms within the duodenal lumen.
Regulation of Pancreatic Exocrine Secretion
- Hormonal control of pancreatic exocrine secretion is regulated by factors such as cholecystokinin (CCK) and secretin.
Test your knowledge on salivary secretion in gastrointestinal physiology including major secretions, regulation, and salivary gland anatomy.
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