GI S6 - Liver & Bile

Question 0

What are the functions of the pancreas

Answer 0

Endocrine secretions

Exocrine secretions

Question 1

What happens to chyme when it leaves the stomach?

Answer 1

Acidity is corrected by the addition of alkali secretions in bile
Hypotonicity is corrected by mass water movement in the duodenum
Digestion is continued by enzyme secretions

Question 2

Describe the endocrine function of the pancreas

Answer 2

In the islets of langerhans

Secrete insulin and glucagon in response to changes in plasma glucose concentration

Question 3

Describe the exocrine function of the pancreas

Answer 3

In acini and ducts
Acini produce enzymes in neutral isotonic solution which are carried to the gut lumen via the ducts
The enzymes are transported as inactive precursors, zymogens

Question 4

Name some enzymes secreted by the acini

Answer 4

Trypsinogen
Carboxypeptidases
Elastase
Chymotrypsin
Amylases
Lipases

Question 5

Why are enzymes secreted as zymogens?

Answer 5

Inappropriate activation in the ducts causes severe inflammation and so pancreatitis

Question 6

What is a clear diagnostic test of pancreatitis?

Answer 6

When pancreatic enzymes (especially amylase) are found in the blood, it means pancreatic cells are damaged

Question 7

How is acinar secretion controlled?

Answer 7

Stimulated by CCK (cholecystokinin), which is secreted from I cells in the duodenum in response to hypertonicity and peptides in the lumen
Also stimulates by ACh via the parasympathetic postganglionic fibres of the vagus nerve

Question 8

What is the function of ducts?

Answer 8

Carry pancreatic enzymes to the duodenum

Pump HCO3 into the lumen from the ECF

Question 9

Describe the mechanism by which HCO3 is secreted

Answer 9

H+ ions are expelled across the basolateral membrane using energy derived from the inward movement of Na
These combine with HCO3 to form H2O and CO2
CO2 enters the cell, where HCO3 and H+ are regenerated
HCO3 is secreted into the lumen and H+ is free to restart the cycle

Question 10

How is duct cell HCO3 secretion controlled?

Answer 10

Jejunal S cells produce secretin in response to low pH

The effect of secretin is potentiated by CCK

Question 11

How can the functions of the liver be broadly classified?

Answer 11

Those related to the blood

Those related to the gut

Question 12

What are some blood related functions of the liver?

Answer 12

Energy storage
Production of various blood components
Detoxification

Question 13

What are some gut related functions of the liver?

Answer 13

The secretion of bile and its components

The excretion of bile pigments, particularly bilirubin

Question 14

What is bile composed of?

Answer 14

The bile acid dependent and bile acid independent fractions

Question 15

Describe the bile acid dependent fraction

Answer 15

Secreted by cells lining the canaliculi

Contains bile acids (salts), cholesterol and bile pigments

Question 16

Give examples of bile acids

Answer 16

Cholic acid

Deoxycholic acid

Question 17

Describe the bile acid independent fraction

Answer 17

Secreted by cells lining the intrahepatic ducts

Question 18

Describe bile acids/salts

Answer 18

Cholesterol derivatives conjugated with amino acids
Travel in micelles - micro particles made up of bile acids, phospholipids and cholesterol
Play an important part in lipid digestion and absorption

Question 19

Why are bile acids so important for lipid digestion and absorption?

Answer 19

Lipids are hydrophobic so aggregate into large globules which decreases surface area available for enzymatic digestion
Micelles increase surface area so increase rate of lipid digestion
They also carry lipids through the “unstirred layer” to the epithelial cells where the fatty acids can diffuse in

Question 20

What happens to bile acids after the lipids have been digested and absorbed?

Answer 20

Apart from a small proportion de conjugated by bacterial action, the bile salts remain in the gut until the terminal ileum, where they are absorbed.
From there, they are transported back to the liver via the portal vein from where they are resecreted or stored in the gall bladder

Question 21

How do gall stones form?

Answer 21

Bile acids are stored in the gall bladder, but their volume is reduced as they are concentrated.
Crystals can form and if they move into the neck of the gall bladder, obstruction can occur, causing the intense pain of biliary colic
Obstruction often leads to inflammation and infection

Question 22

How is bile acid secretion controlled?

Answer 22

CCK induces the release of bile acids from storage by causing contraction of the smooth muscle of the walls of the gall bladder and ducts

Question 23

What can often be the result of a problem with bile acid secretion?

Answer 23

Improper lipid digestion
Therefore lipid in the faeces
Known as steatorrhoea
‘Pale, light and offensive’

Question 24

Describe cirrhosis

Answer 24

Often seen in alcoholics
Progressive destruction of hepatocytes and replacement with fibrous tissue
Fibrous tissue surrounds intrahepatic vessels so impedes circulation and makes the liver firm
This increases pressure, causing portal hypertension

Question 25

What can portal hypertension cause?

Answer 25

Dilation at points of anastomoses causes varicose veins, which may rupture and cause haemorrhage
You can get oesophageal varices and haemorrhoids
Ascites
Caput medusa