Session 6 - Pancreas And Liver

Question 1

Describe the properties of chyme.

Answer 1

Low pH
Hypertonic (very concentrated)
Partially digested

Question 2

What is the role of Brunner’s glands?

Answer 2

Secrete alkaline mucus, protecting cells lining the duodenum from acidic chyme.

Question 3

How is the water content of chyme modified in the duodenum?

Answer 3

Water is added to the chyme, changing it from hypertonic when it enters the duodenum to isotonic when it leaves the duodenum.
Duodenum is relatively permeable to water so hypertonic chyme draws water into lumen from ECF/circulation.

Question 4

Why does the release of chyme from the stomach into the duodenum need to be controlled?

Answer 4

Needs controlling so as not to overwhelm the duodenum, as if it was released too quickly there would be a massive influx of water from the ECF/circulation into the lumen due to the hypertonic nature of stomach chyme.

Question 5

What is secreted by the duodenum in response to the presence of chyme?

Answer 5

Secretin

Cholecystokinin (CCK)

Question 6

What is the effect of CCK on the pancreas and gallbladder?

Answer 6

Action on pancreas:

• stimulates the release of aqueous bicarbonate (HCO3-)
• stimulates the release of enzymes

Action on gallbladder:

• contracts gallbladder
• relaxes sphincter of oddi

Question 7

What is the effect of autonomic stimulation on pancreatic secretions?

Answer 7

Sympathetic inhibits pancreatic exocrine function

Parasympathetic (vagus) stimulates pancreatic exocrine function.

Question 8

Which enzymes are active in the pancreas and which ones are inactive?

Answer 8

Amylases and lipases are active whilst stored in the pancreas.
Proteases are inactive whilst stored in the pancreas.

Question 9

Give examples of activated proteases.

Answer 9

Trypsin
Chymotrypsin
Elastase
Carboxypeptidase

Question 10

Pancreatic enzymes are produced in what cells?

Answer 10

Acinar cells

Question 11

How are proteases stored in the pancreas?

Answer 11

Inactive proteases are concentrated and stored in zymogen granules.

Question 12

What do duct cells of the pancreas secrete?

Answer 12

Aqueous component (isotonic)
Bicarbonate

Question 13

How do pancreatic secretions reach the duodenum?

Answer 13

Via the pancreatic duct and then the Ampulla of Vater

Question 14

What is the commonest cause of pancreatitis?

Answer 14

Gallstones

Question 15

What does the liver secrete into the duodenum?

Answer 15

Bile

Question 16

Where is bile stored until it is released into the duodenum?

Answer 16

Gallbladder

Question 17

What does bile consist of?

Answer 17

Bile acids
Bile pigments
Alkaline solution

Question 18

What is the role of bile in fat digestion?

Answer 18

Emulsifies lipids in the duodenum so that they can be readily digested by lipases secreted from the pancreas.

Question 19

What is the main functional cell of the liver?

Answer 19

Hepatocytes

Question 20

All blood from the gut drains into the liver via what vein?

Answer 20

Hepatic portal vein

Question 21

Describe the structure of a liver lobule.

Answer 21

Hexagonal arrangement
Triad of structures at each corner:
- branch of portal vein
- branch of hepatic artery 
- bile duct
Central hepatic vein in the middle
Blood enters lobule via hepatic artery and portal vein

Question 22

In liver lobules, blood flows in towards central vein via what vessels?

Answer 22

Sinusoids

Question 23

Describe the route of bile as it flows out of a liver lobule.

Answer 23

Bile flows out along canaliculi, into a bile duct which then joins to the common bile duct.

Question 24

Blood drains from the periphery of a lobule to the centre. Which area of the lobule is going to be most affected by toxins and which by ischaemia?

Answer 24

Periphery will be most affected by toxins as it is the first area to be exposed to toxins in the blood, centre less likely to be exposed.
Central cells will be the most affected by ischaemia as they are furthest from the blood supply and therefore the least well oxygenated.

Question 25

What cells produce bile and which components of bile do they produce?

Answer 25

Hepatocytes - produce bile salts and pigments

Bile duct cells - produce alkaline juices (stimulated by secretin)

Question 26

What happens to bile whilst it is being stored in the gallbladder?

Answer 26

Bile becomes concentrated (water/ions removed)

This can lead to gallstones

Question 27

What stimulates gallbladder contraction?

Answer 27

CCK release from the duodenum

Question 28

How does bile reach the duodenum from the gallbladder?

Answer 28

Bile is secreted via the common bile duct then the ampulla of vater into the duodenum.

Question 29

What are bile salts?

Answer 29

Bile salts are bile acids conjugated with amino acids.

Question 30

Why are bile acids conjugated to form bile salts?

Answer 30

Bile salts are better at emulsifying lipids in the duodenum than bile acids.

Bile acids are not always soluble at duodenal pHs (making them functionally useless).

Bile salts have an amphipathic structure (hydrophobic end and hydrophilic end), so are both water and lipid soluble.

Question 31

What are the two primary bile acids?

Answer 31

Cholic acid

Chenodeoxycolic acid

Question 32

Why do lipids need to be emulsified?

Answer 32

Lipids tend to form large globules by the time they reach the duodenum - small surface ares for lipases to act on.

Bile salts emulsify fat into smaller units - disperses droplets increasing surface area for lipases to act on.

Bile salts then create micelles with the products of lipid breakdown - micelles act as transporter for hydrophobic molecules (products of lipid digestion) towards enterocytes.

Question 33

Describe the entero-hepatic circulation of bile acids.

Answer 33

Bile salts remain in the gut, do not enter enterocytes.
Reabsorbed in the terminal ileum.
Returned to the liver in portal blood.
Liver recycles bile acids (does not have to re-synthesise large volumes).

Question 34

Give examples of the lipid products of digestion.

Answer 34

Cholesterol
Monoglycerides
Free fatty acids

Question 35

What happens to lipid molecules after they enter the enterocyte?

Answer 35

Inside the enterocyte lipid molecules are built back up again (re-estified) back to triglycerides, phospholipids and cholesterol.

They becomes packed with apoproteins to form chylomicrons.

The chylomicrons are exocytosed from the basolateral membrane of the enterocytes into the interstitial fluid.

Chylomicrons are too large to be taken up by capillaries, so instead enter lymphatic capillaries and drain into the thoracic duct.

Question 36

What is steatorrhoea and what causes it?

Answer 36

Steatorrhoea is the presence of undigested fat in faeces.
Faeces will appear pale, floating, foul smelling.
Due to certain pathologies which cause bile acids (salts) or pancreatic lipases to not be secreted in adequate amounts.