9. Pancreas And Liver

Question 1

What in the duodenum secrete alkaline mucosa, protecting the cells lining the duodenum from acidic chyme?

Answer 1

Brunner’s glands

Question 2

Why is chyme hypertonic?

Answer 2

Stomach wall is largely impermeable to water, so water cannot move in to dilute the chyme.

Question 3

How does the fact chyme is hypertonic allow for further digestion of chyme within the duodenum?

Answer 3

Draws movement of water from extracellular fluid and circulation into the duodenum, making it isotonic.

Question 4

What secretions from the pancreas and liver allow for further digestion of chyme within the duodenum?

Answer 4

Pancreas - enzymes and bicarbonate.

Liver - bicarbonate and bile.

Question 5

What does secretin stimulate the release of from the pancreas?

Answer 5

Acts on the pancreas to stimulate that release of an aqueous bicarbonate component of pancreatic secretion.

Question 6

What does cholecystokinin stimulate the release of in the pancreas?

Answer 6

CCK acts on the pancreas to stimulate the release of the enzyme component of pancreatic secretion.

Question 7

What affect does cholecystokinin have on the gallbladder?

Answer 7

Contracts the gallbladder and relaxes the sphincter of oddi.

Question 8

Where is secretin released from, and in response to what?

Answer 8

Released from the duodenum in response to the low pH of chyme.

Question 9

Where is cholecystokinin released from and in response from what?

Answer 9

Duodenum, in response to hypertonicity/small peptide/fats within chyme in the duodenum.

Question 10

Whilst pancreatic secretions are stimulated by hormones (secretin and CCK), what else are they stimulated by?

Answer 10

Autonomic - sympathetic inhibits secretion and parasympathetic (vagus) stimulates secretion.

Question 11

What cells in the pancreas produce enzymes?

Answer 11

Acini

Question 12

What enzymes are produced by the acinar cells of the pancreas?

Answer 12

Active amylase and lipases.

Inactive proteases.

Question 13

Name 3 proteases (when activated) produced by the acinar cells of the pancreas. What type of proteases are these?

Answer 13

Endopeptidases (produce shorter polypeptides):
Trypsin.
Chymotrypsin.
Elastase.
Exopeptidases (produce dipeptides or amino acids):
Carboxypeptidase.

Question 14

What are inactive protease enzymes stored in in acinar cells?

Answer 14

Zymogen granules as zymogen.

Question 15

What do duct cells of the pancreas secrete?

Answer 15

Aqueous component (isotonic) and bicarbonate.

Question 16

Why can gallstones lead to pancreatitis?

Answer 16

If gallstone is blocking distill end of the common bile duct at the ampulla of vater, then this also blocks secretions from the pancreatic duct. Proteases build up in the pancreas and it starts to digest itself.

Question 17

What does bile consist of?

Answer 17

Bile acids and bile pigments.

Alkaline solution.

Question 18

What is the role of bile acids and pigments in the duodenum?

Answer 18

Emulsify fat so they can be readily digested by lipases secreted but the pancreas.

Question 19

Why is the liver highly metabolically active?

Answer 19

Produced proteins and lipids for export.

Question 20

Via what vein does blood from the gut drain into the liver?

Answer 20

Portal vein.

Question 21

In a liver lobule, blood flows in towards the central vein from the portal triad via what?

Answer 21

Sinusoids.

Question 22

In a liver lobule bile acids and pigments flow out from the hepatocytes to the bile duct in the portal triad via what?

Answer 22

Canaliculi.

Question 23

Why are cells in zone 1 of a liver lobule more likely to be affected by toxic substances?

Answer 23

Substances are brought to the liver from the gut and and therefore start at the periphery and work towards the middle.

Question 24

Why are cells in zone 3 of a liver lobule more likely to be affected by ischaemia?

Answer 24

Cells at the periphery are better oxygenated as arterial blood starts at the periphery and works towards the middle.

Question 25

What role of the gallbladder in modification of bile can lead to gallstones?

Answer 25

Concentrates the bile (removed water and ions) .

Question 26

Bile acids and pigments are produced by hepatocytes in the liver. What cells secrete the alkaline juices component of bile?

Answer 26

Bile duct cells.

Question 27

What are bile salts?

Answer 27

Bile acids conjugated with amino acids.

Question 28

What are the two primary types of bile acids?

Answer 28

Cholic acid and chenodeoxycolic acid.

Question 29

Why are bile acids conjugated into bile salts

Answer 29

Bile salts are far better at emulsifying fats in the duodenum:
Bile acids are not always soluble at duodenal pH. Bile salts have an amphipathic structure and so allow emulsification of dietary lipids.

Question 30

Why do lipids need emulsifying by bile salts?

Answer 30

Lipids tend to form large globules by the time they reach the duodenum, meaning there is a small surface area for lipases to act. Therefore bile salts emulsify fat into smaller units, dispersing the droplets to increase surface area, thus allowing lipases to act.

Question 31

What are micelles?

Answer 31

Are created when bile salts emulsify products of lipid breakdown. Are a vehicle fro transporting hydrophobic molecules (products of lipid digestion) to the luminal membrane of the enterocyte.

Question 32

What happens once the lipids, carried to the enterocyte by micelles, diffuse into the enterocyte?

Answer 32

Lipids are re-esterified (built back up as had to be broken down to fit through the wall of the enterocyte) to triglycerides, phospholipids and cholesterol. They are then packed with apoproteins within the enterocyte (forming chylomicrons).

Question 33

What happens when chylomicrons are exocytosed from the basolateral membrane of the enterocyte?

Answer 33

Enter into the lymphatic capillaries and then thoracic duct.

Question 34

What is steatorrhoea?

Answer 34

Undigested fat appearing in faeces which is pale, floating and foul smelling, as a result of certain pathologies that cause bile acids salts) or pancreatic lipases to not be secreted in adequate amounts.

Question 35

What happens to bile salts when they reach the enterocytes with lipids as micelles?

Answer 35

Bile salts remain in the gut (don’t enter the enterocyte). Are reabsorbed in the terminal ileum and are returned to the liver in the portal blood, where the liver recycles the bile salts.

Question 36

Where are bile acids conjugated into salts?

Answer 36

In the liver, by the hepatocytes.

Question 37

Why are pancreatic proteases released in inactive forms?

Answer 37

To prevent them from digesting the pancreas itself.

Question 38

In acute pancreatitis, which enzymes can be found in the blood?

Answer 38

Amylase and proteases.