Metabolism in the liver Flashcards
What are the functions of the liver?
- Carbohydrate metabolism
- Protein metabolism
- Fat metabolims
- Detoxification
- Pathogens
- Bile manufacture
How are carbohydrates broken down after meals?
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
How is blood glucose maintained in a fasting state (a few hours after a meal)?
primarily glycogen > glucose
but also fat stores > glycogen > glucose
last resort amino acids > glucose
What is the process of glycogenolysis
glycogen > glucose
- using glycogen phosphorylase
- triggered by glucagon catecholamines
By what processes are fats broken down to release energy
1) Fat stores under influence of glucagon, cortisol and catecholamines > (lipolysis) glycerol > (gluconeogenesis) glucose > energy
2) Fat stores > fatty acids > ketones releasing ATP
How are cholesterol and lipoproteins synthesised?
Fatty acids > Acetyl CoA > Cholesterol > (+ proteins a.g triglyceride or phospholipids) lipoproteins
What is the process of amino acid conversion to ammonia to release energy called?
Deamination
ammonia then converted to urea using urea cycle and excreted via kidneys
What is the function of plasma proteins?
1) transport
2) coagulation
3) exertion of plasma oncotic pressure to prevent fluid leakage or entry
What is the process by which Vitamin D is activated?
cholecalciferol > 25-(OH)-cholecalciferol > 1,25-(OH)2-cholecalciferol
What vitamins are stored in the liver?
ADEK
Give examples of substances detoxified in the liver?
- 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
What are the functions of bile?
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
What are some of the key components of bile?
- Primarily water
- Electrolytes
- Bile acids
- Bile pigments
- cholesterol, phospholipids and fat
What is the first step in bilirubin breakdown (outside hepatocytes)
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
What steps in the breakdown of bilirubin occur in the hepatocytes?
3) Bilirubin + glucoronic acid using glucuronyl transferase to form bilirubin diglucuronide
4) Bilirubin diglucuronide leaves hepatocytes via multi drug resistant protein 2
What are the final steps in bilirubin breakdown (occurring in intestines)?
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
What are gallstones and how are they caused?
Caused by high levels of cholesterol or bilirubin in the bile
Either cholesterol crystals or calcium bilirubinate form
Symptoms of gallstones?
Usually symptomless until you get sudden onset severe abdominal pain in epigastric or RUQ which can radiate to shoulder (often triggered by fatty foods)
Risk factors for gallstones?
- Female
- Obese
- 40+
- Conditions which affect bile flow e.g cirrhosis or primary sclerosing cholangitis
- Crohns or IBS
- Recent weight loss
What are the causes of bilirubin build up in blood?
- 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)
How can you test for cause of jaundice?
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
