Liver function Flashcards
What is the role of the liver in energy metabolism?
Convert amino acids into energy (glycolysis)
Store glucose as glycogen
What are the liver enzymes involved in energy metabolism?
Aspartate aminotransferase (AST)
Alanine aminotransferase (ALT)
What is the function of aspartate aminotransferase (AST) in energy metabolism in the liver?
Glycolysis
Role in the malate-asparate shuttle
Aspartate can be converted to malate in a reversible reaction (intermediate = oxaloacetate)
Malate is produced in the cytoplasm and then converted back to aspartate in the mitochondria
Malate -> oxaloacetate in the mitochondria produces NADH
NADH is then used to produce ATP by oxidative phosphorylation
AST catalyses the conversion between aspartate and oxaloacetate
What is the role of alanine aminotransferase (ALT) in energy metaolism in the liver?
Gluconeogenesis
Amino acid catabolism
Alanine reacts with alpha-ketoglutarate to form glutamate and pyruvate (catalyzed by ALT)
Pyruvate can be used to produce glucose or enter the Kreb’s cycle
How can liver enzymes be used to diagnose liver damage?
AST and ALT are only found in the blood when liver damage is present
Name some plasma proteins produced by the liver
Serum albumin
VLDL (very low density lipoproteins)
HDL (high density lipoproteins)
Fibrinogen
Prothrombin
Transferring
Complement proteins
What is the role of albumin in plasma?
carrier protein
maintains osmotic pressure
Describe lipoproteins
Lipoproteins move insoluble fat around e.g., triglycerides, cholesterol esters
Describe according to density e.g, VLDL, HDL
Linked to proteins (apolipoproteins)
What are the functions of apolipoproteins?
activate enzymes
bind receptors
stabilise lipoprotein
Describe the synthesis of cholesterol in the liver
Acetyl-CoA + actetoacetyl-CoA
Carbon chain lengthens
Decarboxylation => cholesterol
Cholesterol can then be converted to bile salts in the liver or moved to endocrine glands to become steroid hormones
How are bile salts formed in the liver?
Bile acids are cholesterol derivatives
Cholic acid (main bile acid) conjugates with amino acids to reduce the pK of amino acids so they exist in ionised forms as bile salts
What are micelles?
aggregates of bile salts in aqueous solution (conjugated with cholesterol and phospholipids) formed in the SI
amphiphilic - -ve outside (water soluble exterior) and +ve inside (lipid core)
-ve external charge prevents coallescing/clumping
What is the action of bile?
Acts as a detergent to emulsify fats (increase SA) => smaller fat droplets
Hydrophobic side of associates with lipids and hydrophilic side with water => emulsification
Also important part of absorbing fat soluble vitamins (A, D, E, K)
phospholipids are hydrolysed by pancreatic phospholipase, cholesterol by a cholesterol esterase
Describe the route of bile acids
Absorbed in ileum
travel to liver via hepatic portal vein
conjugate with cholesterol
travel to gall bladder then into the duodenum where they cause fat absorption
travel down to ileum and reabsorbed
How is fat absorbed in the small intestine?
Bile salts and pancreatic lipase break large fat droplets down
Micelles formed as bile salts form aggregates, conjugated with phospholipids and cholesterol
Micelles release into epithelial cells/enterocytes
Free fatty acids and monoglycerides within mycelle diffuse into enterocyte
Triglycerides resynthesised and chylomicrons formed in enterocyte (chylomicrons are exocytosed into lymph vessel)
