Metabolism in the liver

Question 1

What are the functions of the liver?

Answer 1

• Carbohydrate metabolism
• Protein metabolism
• Fat metabolims
• Detoxification
• Pathogens
• Bile manufacture

Question 2

How are carbohydrates broken down after meals?

Answer 2

1) Carbs > absorbed and broken down into Fructose, galactose and glucose (in GIT)
2) Fructose and Galactose can be converted to Glucose (Liver)
3) Glucose > Glycogen (using glycogen synthase and under influence of insulin)
4) some glucose can also be used immediately for energy

Question 3

How is blood glucose maintained in a fasting state (a few hours after a meal)?

Answer 3

primarily glycogen > glucose
but also fat stores > glycogen > glucose
last resort amino acids > glucose

Question 4

What is the process of glycogenolysis

Answer 4

glycogen > glucose

• using glycogen phosphorylase
• triggered by glucagon catecholamines

Question 5

By what processes are fats broken down to release energy

Answer 5

1) Fat stores under influence of glucagon, cortisol and catecholamines > (lipolysis) glycerol > (gluconeogenesis) glucose > energy
2) Fat stores > fatty acids > ketones releasing ATP

Question 6

How are cholesterol and lipoproteins synthesised?

Answer 6

Fatty acids > Acetyl CoA > Cholesterol > (+ proteins a.g triglyceride or phospholipids) lipoproteins

Question 7

What is the process of amino acid conversion to ammonia to release energy called?

Answer 7

Deamination

ammonia then converted to urea using urea cycle and excreted via kidneys

Question 8

What is the function of plasma proteins?

Answer 8

1) transport
2) coagulation
3) exertion of plasma oncotic pressure to prevent fluid leakage or entry

Question 9

What is the process by which Vitamin D is activated?

Answer 9

cholecalciferol > 25-(OH)-cholecalciferol > 1,25-(OH)2-cholecalciferol

Question 10

What vitamins are stored in the liver?

Answer 10

ADEK

Question 11

Give examples of substances detoxified in the liver?

Answer 11

• Job of kupffer cells
• haemoglobin
• cholesterol, drugs, alcohol, poisons
• fat and water soluble drugs (water soluble excreted via bile and urine)
• trace metals, steroids and ammonia

Question 12

What are the functions of bile?

Answer 12

1) excretion of products of haemoglobin breakdown i.e. bilirubin
2) digestion of fats, bile acids can make fast soluble by rearranging them to form micelles which are then able to be emulsified

Question 13

What are some of the key components of bile?

Answer 13

• Primarily water
• Electrolytes
• Bile acids
• Bile pigments
• cholesterol, phospholipids and fat

Question 14

What is the first step in bilirubin breakdown (outside hepatocytes)

Answer 14

1) Bilirubin binds to albumin (too make molecule bigger so it isn’t excreted in kidneys)
2) Then absorbed into hepatocytes using organic anion transport polypeptide

Question 15

What steps in the breakdown of bilirubin occur in the hepatocytes?

Answer 15

3) Bilirubin + glucoronic acid using glucuronyl transferase to form bilirubin diglucuronide
4) Bilirubin diglucuronide leaves hepatocytes via multi drug resistant protein 2

Question 16

What are the final steps in bilirubin breakdown (occurring in intestines)?

Answer 16

5) bilirubin diglucuronide enters bile which travels to intestines
6) bacteria in intestines break compound into urobilinogens
7) These can be reabsorbed back into plasma via enterohepatic circulation or excreted via urine or faeces if in excess

Question 17

What are gallstones and how are they caused?

Answer 17

Caused by high levels of cholesterol or bilirubin in the bile
Either cholesterol crystals or calcium bilirubinate form

Question 18

Symptoms of gallstones?

Answer 18

Usually symptomless until you get sudden onset severe abdominal pain in epigastric or RUQ which can radiate to shoulder (often triggered by fatty foods)

Question 19

Risk factors for gallstones?

Answer 19

• Female
• Obese
• 40+
• Conditions which affect bile flow e.g cirrhosis or primary sclerosing cholangitis
• Crohns or IBS
• Recent weight loss

Question 20

What are the causes of bilirubin build up in blood?

Answer 20

• Excess production of bilirubin (pre-hepatic)
• Decreased uptake of bilirubin (hepatic)
• Disturbed binding of bilirubin for excretion (hepatic)
• insufficient transport of conjugated bilirubin into canaliculi (hepatic)
• Bile duct or gallbladder obstruction (post-hepatic)

Question 21

How can you test for cause of jaundice?

Answer 21

If conjugated bilirubin present in urine (will be dark) cause is post-hepatic and if no bile in faces (will appear white) then post-hepatic