L5: functions and secretions of pancreas

Question 1

Functions of the pancreas

Answer 1

Exocrine - produces pancreatic juice:

• 99% of cell mass
• acinar cells and duct cells
• juices released into duodenum
• breaks down all categories of foodstuff

Also endocrine - produces hormones

Question 2

What is the opening in the duodenum that the pancreatic duct leads to called?

Answer 2

Ampulla of Vater - muscular structure surrounding bile and pancreatic ducts as they enter duodenal wall
(Pic at 5:15)

Question 3

What happens when there is pancreatic insufficiency?

Answer 3

Pancreatic insufficiency will cause maldigestion of proteins, fats, and carbohydrates. Lack of bicarbonate ions can lead to ulcers, inability to form micelles etc.
But the pancreas has a huge functional reserve for its exocrine activities so insufficiency only occurs when 90% of function is lost.

Question 4

Exocrine secretions of the pancreas

Answer 4

• digestive enzymes: proteases, lipases, carbohydrases, nucleases
• alkaline juice (rich in bicarbonate ions): neutralises gastric acid; prevents ulcer formation; enables pancreatic enzymes to work; enables micelle formation

Question 5

Control of pancreatic secretion

Answer 5

Acidic chyme entering the duodenum causes the enteroendocrine cells of the duodenal wall to release secretin, whereas fatty, protein-rich chyme (mainly lipids) induces release of CCK
Secretin and CCK enter bloodstream
Upon reaching the pancreas, CCK induces the secretion of enzyme-rich pancreatic juice and will cause gallbladder to cause lipid digestion; secretin causes copious secretion of bicarbonate rich pancreatic juice
Both inhibit stomach acid secretion

Question 6

What are the cellular locations of different pancreatic secretions?

Answer 6

Acinar cells:

• Specialised for production and export of large quantities of digestive enzymes.
• Stimulated by primarily CCK to release enzymes
• secretin and ACh can also induce acinar cell enzyme release

Duct cells:

• Specialised for transport of electrolytes. A bicarbonate rich juice is released from the pancreas after eating but a chloride rich juice is secreted when flow rates are low.
• Stimulated by secretin to release a bicarbonate rich juice.
• ACh can also induce duct cell bicarbonate release

Question 7

What does secretin do to centroacinar and upper ductal cells?

Answer 7

• carbon dioxide enters the cell and goes through its reaction to become bicarbonate and a proton
• the bicarbonate is destined to go into the duodenum. So it will enter the pancreatic lumen duct in exchange for chloride.
• the proton produced from this reaction will move out into the bloodstream, to neutralise the pH from the gastric ‘alkaline tide’ but reacting with the excess bicarbonate ions.

Question 8

How is there enough chloride in the pancreatic duct lumen for the bicarbonate chloride exchange?

Answer 8

There is a CTFR channel = cystic fibrosis transmembrane channel regulator
It will move chloride into the lumen so it can be exchanged,
Bicarbonate ions can move through this channel as well as the bicarbonate/chloride channel, to enter the lumen.
It is stimulated to open by secretin.
Water follows osmotically.

Question 9

What happens in cystic fibrosis?

Answer 9

The CFTR channels do not work properly, so water does not follow into the lumen, meaning the pancreatic juices are not very watery and able to move through the ducts as well, so issues digesting food,

Question 10

How is the alkaline tide created and neutralised?

Answer 10

1. Stomach parietal cells send H+ (acid) into the stomach and bicarbonate into the bloodstream/plasma.
2. Bicarbonate in the plasma causes an alkaline tide which increases plasma pH.
3. When gastric acid arrives in the duodenum, sensitive cells release secretin. This sends signals to the pancreas to send bicarbonate into the duodenum and H+ into the plasma.
4. Pancreatic bicarbonate entering the duodenum will neutralise the acid from the stomach.
5. Pancreatic H+ entering the plasma will neutralise the alkaline tide caused by the stomach.

Question 11

What does the vagus nerve do to the pancreas?

Answer 11

Vagus nerve stimulates the pancreas as well to make the bicarbonate and digestive enzymes.

Question 12

What are the relative proportions of enzymes in pancreatic juice?

Answer 12

90% proteases
7% amylases
2% lipases
<1% nucleases

KEY POINT: predominantly proteases compose the pancreatic juice

Question 13

How does the body prevent auto digestion of the pancreas since there are many digestive enzymes in the juice?

Answer 13

The digestive enzymes are secreted from the pancreas as inactive zymogens, which only become activated once in the SI, to prevent auto digestion of the pancreas.
Once pancreatic trypsinogen, a protease, enters the SI, it is converted into the active digestive protease trypsin by enterokinase - an enzyme found in the brush border of villi cells.
Trypsin is then able to activate other inactive zymogens.
Pancreas also has trypsin inhibitors which prevent autodigestion.

Question 14

Where is enterokinase found?

Answer 14

The brush border cells of the villi

Question 15

Link between poor oral health and pancreatic cancer?

Answer 15

Potential periodontal disease links to pancreatic cancer.

Lots of inflammation in the mouth: releases lots of inflammatory markers which can lead to cancer cells in the pancreas.