Flashcards in Exam #5: Gastric Secretions Deck (27):
What are the secretory products of parietal cells? Where are these cells located?
Parietal cells secrete HCl & Intrinsic Factor
- HCl functions in protein digestion, sterilization, nutrient absorption
- Intrinsic Factor= Vitamin B absorption
****Parietal cells are located in the body of the stomach
What is the secretory product of chief cells? Where are these cells located?
Chief cells secrete pepsinogen, which functions in protein digestion
*****Chief cells are located in BOTH the body & antrum of the stomach
What are ECL cells? Where are these cells located? What is their product?
ECL, or "enterochromaffin-like" cells produce histamine, which promotes HCl secretion
*****ECL cells are located in the body of the stomach
What is the secretory product of G-cells? Where are these cells located?
G-cells produce gastrin, which promotes HCl secretion
What is the secretory product of D-cells? Where are these cells located?
D-cells produce somatostatin, which suppress HCl secretion
*****antrum of the stomach
What is the secretory product of superficial epithelial/ neck cells? Where are these cells located?
*****Both are gastroprotective & cells are located throughout the entire stomach
How do neuronal pathways regulate acid secretion in the stomach?
- promotion of mucous, bicarbonate, and HCl secretion
How do paracrine pathways regulate acid secretion in the stomach?
Histamine binding to receptors on parietal cells stimulates acid secretion
How do endocrine pathways regulate acid secretion in the stomach?
Gastrin binding to receptors on parietal cells stimulate acid secretion
What are the functions of gastric acid?
1) Protein digestion & conversion of pepsinogen to pepsin (for protein digestion)
2) Provide sterile environment
3) Prevent bacteria and fungal growth
4) Facilitate absorption
5) Promote bile and enzyme flow
What are the positive and negative regulators of gastric acid secretions?
- ACh (neural)
- Histamine (ECL)
- Gastrin (G-cells)
- Somatostatin (D-cells)
What cells release the positive regulators of gastric acid secretion?
What cells release the negative regulators of gastric acid secretion?
D-cell secretion of somatostatin
Describe the steps of how pepsinogen is converted in lumen of the stomach to the active protease pepsin.
- Pepsinogen is secreted by chief cells in the body & antrum of the stomach.
- HCl converts pepsinogen into pepsin (active) i.e. lower pH
- This is protective and ensure that pepsinogen is activated once it is in the lumen of the stomach
- Higher pH inactivates the enzyme
*****ACh is a key stimulus in the secretion of pepsinogen
What is the site of intrinsic factor secretion?
Parietal cells secrete intrinsic factor in the body of the stomach
I.e. damage to parietal cells & the gastric epithelium will result in an inability to absorb Vitamin B12
What is the physiological role of intrinsic factor?
- Complexes with Vitamin B12 in duodenum
- IF + Vitamin B12= absorbed in ileum via receptor mediated endocytosis
No IF= No Vitamin B12 absorption
What are the two key stimuli for mucus secretion by epithelial and neck cells of the stomach?
There are two key regulators
1) ACh (neurocrine)
2) Prostaglandins (paracrine)
****Note that prostaglandins: 1) increase mucus & bicarbonate secretion, 2) suppression of HCl secretion, and 3) increased gastric blood flow
What is the the physiological role of mucus in the stomach?
Gastroprotection; mucus creates a protective layer over the mucosal epithelium
What are the components of mucus?
Outline the pathophysiology of gastritis.
Gastritis= inflammation of gastric mucosa caused by damage to the protective mucosal barrier--this inflammation DOES NOT NECESSARILY produce a break in the mucosal lining. Commonly caused by:
1) H. pylori
2) NSAIDs i.e. ASA
Outline the pathophysiology of H. pylori infection.
- Urease creates a buffered microenvironment that is hospitalble to H. pylori colonization
- Colonization and subsequent immune response cause the mucosal damage that leads to ulceration
Outline the pathophysiology of peptic ulcers.
Break in the protective lining of the lower esophagus, stomach, or duodenum
Outline the pathophysiology of Zollinger-Ellison Syndrome.
Gastrin secreting tumor that results in high acid levels
What are the four different phases of gastric acid secretion?
2) Cephalic= sight or smell of food triggers vagal response to increase acid secretion
3) Gastric= stomach distention & presence of proteins causes vagal response to increase acid secretion
- Most gastric acid secreted in this phase
4) Intestinal= proteins in the duodenum causes acid secretion
How are the four phases of gastric acid secretion regulated?
3) Gastric= if pH falls below 1, feedback on D-cells to secrete somatostatin
4) Intestinal= peptides induce gastrin secretion
Outline the mechanism of HCl production. What cells produce HCl?
Parietal cells secrete HCl i.e. gastric acid via a H+-K+ ATPase, or "proton pump"
- Located on the apical membrane of parietal cells