Topic 53 - Secretion and regulation of gastric juice

Question 1

Words to include in gastric secretion

Answer 1

• Tubular glands of corpus and fundus
• Mucin rich fluid
• Gastric mucosa
  
  • Intrinsic factors
  • Cobalamin (Vitamin B₁₂)
• Regions of the gastric mucosa
  
  • ​Aglandular region
    
    • Microbial digestion (Ru)
  • Cardia
    
    • Mucin
  • Fundus
    
    • Hydrochloric synthesis
    • Pepsinogen synthesis
  • Pylorus
    
    • Mucin
    • Pepsinogen
    • Gastrin
• Chief cells
  
  • Pepsinogen
  • Granules
  • Pepsin
  • Phe, Try, His amino acids
  • Histamine
• Parietal cells
  
  • HCl
  • Luminal surface
  • canaliculi
  • H-K pump
  • Lumen
  • Acetylcholine
    
    • N. vagus
  • Gastrin
    
    • G-cells
  • Histamine
    
    • H-cells
• Neck cells
  
  • Gastric mucosa
  • Mucin

Question 2

Words to include in regulation of gastric juice secretion

Answer 2

• Cephalic phase
  
  • N. vagus
• Gastric phase
  
  • Stretch- and chemoreceptors
  • Acetylcholine
  • Gastrin
  • Histamine
  • Muscarine type acetylcholine receptor (m-ACh)
  • Gastrin receptor
  • H2 type receptor
  • cAMP level
• Intestinal phase
  
  • Duodenum
  • Gastrin secretion
  • Positive feed back
    
    • Polypeptide (entero-oxyntin)
  • Negative feedback
    
    • Secretin
    • CCK (cholecystokinin)
    • GIP (gastric inhibitory peptide)
    • VIP (vasoactive intestinal peptide)
    • Somatosin
  • GI-dilation

Question 3

Topics to include in the essay

Answer 3

1. Gastric secretion
   
   • Regions of the stomach
2. Function of chief cells and parietal cells
3. Regulation of gastric juice secretion
   
   • Cephalic phase
   • Gastric phase
   • Interstitial phase

Question 4

Give the regions with the gastric mucosa, and what are the different regions producing?

Answer 4

1. Aglandular region
   
   • Microbial digestion (ruminants)
2. Cardia
   
   • Mucin
     
     • Protection of gastric mucosa
3. Fundus
   
   • Hydrochloric synthesis
   • Pepsinogen synthesis
4. Pylorus
   
   • Mucin (protection)
   • Pepsinogen (digestion)
   • Gastrin (regulation)

Question 5

What does chief cells produce, and where?

Answer 5

Produce pepsinogen in fundus

Question 6

Pepsinogen

Answer 6

• Pepsinogen is stored in granules
  
  • Its release is mainly stimulated in a parasympathetic way by n. vagus, or by low blood sugar induced by insulin
• Pepsinogen is degraded to pepsin at pH 2. (HCl)
• Pepsin hydrolyses those peptide bonds which consists of Phe, Try and His amino acids, at pH 1.8 - 3.8
• Pepsin activates other pepsinogens in a autocatalytic way
• Histamine release increase pepsinogen
• The higher the concentration of the HCl in the stomach, the higher the pepsinogen release

Question 7

Parietal cells

Answer 7

• Produce HCl in fundus
• The luminal surface of the parietal cells have canaliculi where HCl is produced
• H-K pump can be found in the luminal membrane of the parietal cells
  
  • H⁺ get into lumen
  • K⁺ get into the cell
• HCl production of parietal cells is influenced by neuronal and endocrine regulation
• Receptors of the parietal cells
  
  • Muscarine type acetylcholine receptor (m-Ach)
    
    • Acetylcholine (released from n. vagus)
  • ​Gastrin receptor
    
    • Gastrin (released from G-cells)
  • H2 type receptor
    
    • Histamine (produced by H-cells)

Question 8

Neck cells

Answer 8

• Epithelial cells of gastric mucosa
• Secrete mucin in antrum

Question 9

Role of mucin

Answer 9

protective role against the strongly acetic gastric juice, protects the wall from “self-digestion”

Question 10

Give the phases of the regulation of the gastric secretion

Answer 10

1. Cephalic phase
2. Gastric phase
3. Interstitial phase

Question 11

Cephalic phase

Answer 11

• Food gets into the mouth and gastric secretion occurs
• Food in the mouth stimulates the taste buds → afferentation CNS
• Efferentation gets to the stomach → gastric juice secretion
• N. vagus cause an increase in gastric secretion
  
  • Directly: Stimulates chief cells and parietal cells
  • Indirectly: Stimulating G-cells (Gastrin producing cells)

Question 12

Gastric phase

Answer 12

• Gastric content stimulates stretch- and chemoreceptors in the mucosa
• Mechanical effects stimulate the chief and parietal cells
• Chemical stimuli activate G-cells, which due to gastrin secretion indirectly increases the production of gastric secretion until the gastric H⁺ ion concentration reaches pH 3
• Substances regulating the HCl production of the parietal cells:
  
  • Acetylcholine
  • Gastrin
  • Histamine

Question 13

Gastric phase

Explane the regulation of gastric secretion

Answer 13

• Activity of the CNS is expressed through N. vagus
• The transmitter is acetylcholine
• G-cells synthesize gastrin
  
  • Fund in pylorus
• H-cells synthesize histamine, which has a paracrine effect on the pareital cells

Question 14

Interstitial phase

Answer 14

• Slight increase in the gastric juice secretion if a substances get into the duodenum which induce gastrin secretion
• Negative feedback:
  
  • Chemical: duodenum is strongly acidic, hyperosmotic
  • Mechanical: expansion of duodenum
• Hormones important for the feedback mechanism of the interstitial phase:
  
  • Secretin
  • CCK (cholecytokinin)
  • GIP (Gastric Inhibitiory Peptide)
  • VIP (Vasoactive Intestinal Peptide)