5)Salivary Secretion in Gastrointestinal Physiology

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Questions and Answers

What is the main function of HCl secreted by the gastric parietal cells?

To kill microorganisms in the stomach

To denature proteins in food

To aid in the breakdown of connective tissue and muscle fibers

To activate pepsinogen into pepsin (correct)

What is the primary role of the mucus coating over the gastric mucosa?

To neutralize acid in the vicinity of the mucosa

To serve as a physical barrier to acid penetration

To prevent HCl from penetrating into the gastric cells

Both a and b (correct)

Which of the following is NOT a function of HCl secreted by gastric parietal cells?

Activating pepsinogen

Stimulating the secretion of gastric juice (correct)

Denaturing proteins

Aiding in the breakdown of food particles

What is the purpose of the tight junctions between the gastric mucosal cells?

To prevent HCl from penetrating between the cells Signup and view all the answers

Which of the following is the main function of the HCO3- -rich mucus?

To neutralize acid in the vicinity of the mucosa Signup and view all the answers

Where is pepsinogen, the inactive precursor to pepsin, secreted from?

Gastric chief cells and mucous cells Signup and view all the answers

What is the main stimulus for fluid and electrolyte secretion in salivary glands?

Parasympathetic innervation Signup and view all the answers

What is the composition of saliva compared to plasma at all flow rates?

Hypotonic Signup and view all the answers

Where is the primary secretion of saliva produced?

In the acinar cell Signup and view all the answers

What ions are absorbed by the duct cells in the salivary glands?

Na+ and Cl- Signup and view all the answers

Which system controls the regulation of salivary secretion?

Nervous system Signup and view all the answers

What is the true statement about fluid secretion in salivary glands?

An active process involving electrolyte transport Signup and view all the answers

What is the role of basic PRPs and histatins in toxin binding?

Preventing the uptake of tannins by intestinal epithelial cells Signup and view all the answers

How does buffering in saliva help counteract the effects of microbial acids?

Forming H2O and CO2 in the presence of H+ Signup and view all the answers

Which proteins in saliva function by attacking microbial cell walls?

Lysozyme and peroxidase Signup and view all the answers

How do urea and ammonia help neutralize acids according to the text?

By forming H2O and CO2 Signup and view all the answers

Which component plays a role in preventing microorganisms from binding to oral tissues?

Salivary agglutinin (gp340) Signup and view all the answers

What is the role of carbonic anhydrase in saliva according to the text?

Forming H2O and CO2 in the presence of H+ Signup and view all the answers

What is the second messenger pathway associated with binding of acetylcholine to muscarinic receptors?

IP3-Ca2+ Signup and view all the answers

What effect does the increase in cytoplasmic Ca2+ have on the secretory cells?

It draws intracellular Cl- into the lumen. Signup and view all the answers

How is water pulled into the lumen during active fluid secretion?

Via aquaporins in the secretory cell membranes. Signup and view all the answers

What process is responsible for the secretion of proteins and glycoproteins in the salivary glands?

Exocytosis Signup and view all the answers

Which neurotransmitter binds to G-protein coupled β-adrenergic receptors to activate cAMP second messenger in serous cells?

Norepinephrine Signup and view all the answers

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 Signup and view all the answers

What type of solution is actively secreted by the duct cells in the pancreas?

Alkaline solution Signup and view all the answers

Which enzyme activates trypsinogen to its active form, trypsin, in the duodenal lumen?

Enteropeptidase Signup and view all the answers

Why must trypsinogen remain inactive within the pancreas?

To prevent proteolytic activity on pancreatic cells Signup and view all the answers

What is the function of trypsin inhibitor within the pancreas?

Inhibit trypsin's activity within the pancreas Signup and view all the answers

Which enzymes are activated by trypsin within the duodenal lumen?

Chymotrypsinogen and procarboxypeptidase Signup and view all the answers

What role does enteropeptidase play in pancreatic secretion?

Activates trypsin to trypsinogen Signup and view all the answers

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.

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Test your knowledge on salivary secretion in gastrointestinal physiology including major secretions, regulation, and salivary gland anatomy.