PHYS Gut Secretions II - Week 4

Question 1

How is bile secreted?

Answer 1

From liver via bile ducts.

Question 2

Role of cystic duct

Answer 2

Transports bile btw meals to store in gall bladder.

Question 3

Composition of bile:

Answer 3

Bile salts, cholesterol, lecithin, electrolytes & H2O, bile pigments.

Question 4

Critical electrolyte in bile

Answer 4

Bicarbonate - neutralises acidic chyme in duodenum.

Question 5

Bile pigment source

Answer 5

Breakdown of haem.

Question 6

Describe process of fatty droplet breakdown in duodenum.

Answer 6

Fatty droplets float on top of acidic chyme and enter duodenum from stomach -> mixing contractions of small intestine -> breakdown of fat globules -> smaller droplets -> bile salts & phospholipid lecithin embed themselves around fat droplets -> emulsion droplets -> pancreas secretes co-lipase -> pushes aside bile salts & lecithin to enable pancreatic lipase to enter emulsion droplets -> breakdown of triglycerides -> monoglycerides & fatty acids -> diffusion across intestinal epithelial cells -> bloodstream.

Question 7

When is secretin release triggered and what is the affect?

Answer 7

Release of secretin is triggered – acidic chyme @ duodenal wall ->
stimulate liver -> increased bile production
& stimulates ductal cells of the pancreas -> alkaline secretion.

Question 8

When is CCK release triggered and what is the affect?

Answer 8

Release of CCK is triggered – fat droplets floating above chyme @ duodenal wall ->
stimulate gallbladder -> gallbladder contracts (aided also by vagal stimulation) -> hepatopancreatic sphincter relaxes -> bile enters duodenum.
& stimulates ductal cells of the pancreas -> enzyme-rich pancreatic juices.

Question 9

What cells synthesis & secrete pancreatic enzymes and from what granules?

Answer 9

Acinar cells (exocrine) via zymogen granules.

Question 10

Pancreatic enzymes list. State what enzymes are responsible for protein, TAGs, polysaccharides, nucleic acid digestion. State whether secrete in inactive or active form.

Answer 10

Trypsin, chymotrypsin, elastase (I-A) - break peptide bonds in proteins -> peptide fragments. Carboxypeptidease (I-A) - split terminal aa from carboxyl end of protein. Pancreatic lipase (A) - triacylglycerols -> free FAs & monoglycerides. Cholesterol esterase, phospholipase (A). a-amylase (A) - polysaccharides -> glucose & maltose. Ribonuclease & deoxyribonucleic acids (A) - nucleic acids -> mononucleotides.

Question 11

Causes of pancreatitis.

Answer 11

• Defective ductal secretion of HCO3- & H2O
• Decreased release of pancreatic enzymes
• Inappropriate activation of pancreatic enzymes (i.e., within the pancreas -> auto-digestion of pancreas) .

Question 12

Symptoms of pancreatitis.

Answer 12

• Continuous abdominal pain
• Weight loss
• Steatorrhoea (fat malabsorption)

Question 13

Treatment of pancreatitis.

Answer 13

• Improve nutrition with pancreatic supplements
• Complete abstention from alcohol
• Pain relief.

Question 14

What can auto-digestion of the pancreas be triggered by?

Answer 14

Excessive alcohol intake.

Question 15

Vagal/parasymp nerve regulation of pancreatic secretion entry.

Answer 15

Vagal stimulation causes weak contractions of gallbladder post acidic, fatty chyme entry into duodenum.
During cephalic & gastric phases, vagal nerve fibre stimulation -> pancreatic juice release.

Question 16

What activates trypsinogen, chymotrypsinogen, procarboxypolypeptidase enzymes?

Answer 16

• Trypsinogen -> trypsin via enterokinase (secreted by intestinal mucosa post contact w chyme) OR trypsin that has already been formed from previously secreted trypsinogen.
• Chymotrypsinogen -> chymotrypsin via trypsin
• Procaboxypolypeptidase -> carboxypeptidase via trypsin.

Question 17

What does the pancreas secrete to protect itself from auto-digestion?

Answer 17

Pancreas also secretes trypsin inhibitor which protects pancreas in case of blockage or damage as any trypsin can lead to the activation of enzymes mentioned above and consequent pancreatic auto-digestion, which can be fatal.

Question 18

What secretes enterokinase and when is it secreted?

Answer 18

Secreted by intestinal mucosa (duodenum) post contact w chyme.