54. The exocrine function of the pancreas, pancreas enzymes, regulation of pancreatic juice secretion

Question 1

The exocrine function of the pancreas is producing the pancreatic juice. It has two main roles:

Answer 1

• Neutralize acidic gastric content getting into the duodenum
• Secretes enzymes essential for digestion of proteins, fats and carbohydrates.

Question 2

Pancreatic juice

Answer 2

Exocrine cells of the pancreas is organized into acinar cells, with zymogen granules. The lumen is narrow, and form drainage tubules. The drainage tubules produces bicarbonate. Interlobular ducts are continued as extralobular ducts, which enters the pancreatic ducts that ends in the duodenum.

Question 3

Acinar cell

Answer 3

• Ductus interlobularis: ions equal with plasma concentration is secreted
• Ductus extralobularis: HCO3- is secreted, influenced by secretion
• Main collecting tubule: HCO3- secretion into lumen increases, Cl- is taken up.

Question 4

Enzymes and proenzymes

Answer 4

• Pancreas secrete mainly enzymes in a inactive form, which are activated into the duodenum.
• The activation is initiated by enteropeptidase, which produces trypsin (active) from trypsinogen.
• Trypsinogen activates other proenzymes to active form.

Question 5

Regulation of pancreatic juice secretion

Answer 5

• Secretory activity of ducts and acini are regulated by hormones and neurotransmitters.

a. Parasympathetic → vagal stimulus cause increased enzymatic secretion, and slight increase of electrolytes and water
b. Sympathetic → splanchnic stimulus cause decreased amount of pancreatic juice.

Question 6

1) Cephalic phase

Answer 6

• High protein content, but small amount of juice is released

Question 7

2) Gastric phase

Answer 7

• Parasympathetic effect dominates, gastrin appears in the blood. Enzyme secretion increases.

Question 8

3) Intestinal phase

Answer 8

• Influenced by chime in duodenum and jejunum.
• Slight acidity leads to high volume, much HCO3 and low enzyme content in the juice. Stimulated by secretin.
• Presence of amino acids, fatty acids or monoglycerides leads to pancreatic juice secretion that is rich in enzymes. Stimulated by CCK.