Liver physio Flashcards
functions of liver
- Synthesis of serum proteins (albumin, carrier proteins, coagulation factors, growth factors, hormones)
- Cholesterol synthesis & homeostasis
- Production of bile & bile salts
- Metabolism & heat production
- Conjugation of lipophilic compounds (detoxification)
- Excretion (in bile) of lipophilic compounds (waste)
- Store & regulation of nutrients; glucose buffer
- Storage of vitamins, iron and copper
- Blood reservoir
- Immune function
what do liver metabolise
- nutrients (carbohydrates, lipids, protein)
- toxin & drugs (detoxification)
*maintains energy homeostasis (produce energy when needed)
uses of energy produced by liver
- heat production
- muscle activity
- secretion
- membrane potential
- synthesis of materials
- absorption of food
organs involved in fuel homeostasis
- liver
- adipose tissue
- skeletal muscles
how do liver and adipose tissue communicate for fuel homeostasis
- fatty acids from liver -> stored in adipocyte via VLDL
- glucose from blood can also be stored as fatty acids in adipocyte
how do liver and muscles communicate for fuel homeostasis
- amino acids can be either used by muscles to make protein or used by liver to make protein/ glucose
how do adipose tissue and muscle communicate in fuel homeostasis
- glucose usage: glucose can be used to create fatty acids in adipose tissue OR broken down in muscles to release energy
metabolic function of liver
- body’s central metabolic clearing house -> ensure appropriate level of fuel is available to brain, organs etc
why is liver able to be in charge of body’s metabolism
first pass effect
- all nutrients absorbed by intestines (except fatty acid in lymphatic system) are released to portal vein -> liver
what does the liver do during fasting
- activate glycogen and ketone bodies (longer lasting source of fuel)
what happens to glucose after entering liver via portal vein
- converted to glucose 6-phosphate
- can be stored as glycogen via a series of steps (and vice versa when glucose is needed)
what happens when the body requires energy
glycogen breakdown
- liver converts glycogen back to glucose 6-phosphate
- glucose 6-phosphate broken down to glucose by glucose 6 phosphatase (ONLY FOUND IN LIVER)
*in muscles -> no glucose 6 phosphatases -> glucose 6-phosphate immediately used in metabolism
*glycogen can be broken down to G-6-P in muscles as well -> BUT cannot further breakdown to glucose
what is gluconeogenesis
process by liver (convert other substances to glucose)
- amino acids/ lactate -> converted to pyruvate -> converted to glucose 6-phosphate
how does liver maintain glucose levels during fed & fasting states
*glucose buffer
fed state
- liver 1) absorbs excess blood glucose 2) stores glucose as glycogen
fasting state
- liver ensure continual supply of blood glucose via 1) liver glycogen store breakdown 2) gluconeogenesis
what happens to amino acids when absorbed from portal vein (4)
- used to synthesize proteins (eg albumin, haptoglobin)
- INTERCONVERTED to other amino acids by changing side chains
- broken down and DEAMINATED to ammonia -> urea cycle to form urea -> excreted
- GLUCONEOGENESIS
how are nucleotides (nucleic acid) metabolised
nucleic acid excretion (similar to deamination)
- nucleic acid -> ammonia -> urea cycle to form urea
SYNTHESIS/ SALVAGING of ribonucleotides & deoxyribonucleotides occur in liver
what happens to fat that reaches the liver via lymphatic system
enter liver as LDL, VLDL remnants & chylomicron remnants
- broken down to form triglycerides -> TG can be used to form free fatty acids -> form VLDL to transport around body and supply lipid to other tissues
- free fatty acids from TG can bind to acetyl CoA and undergo TCA cycle to produce energy
- free fatty acids from TG can bind to acetyl CoA to form ketone bodies (soluble and can provide energy to other organs esp brain)
- form cholesterol -> bile acids & bile salts -> excrete into bile canaliculi
what happens to liver fatty acid metabolism during fed & fasting states
fed state
- fatty acids synthesis -> triacylglycerides -> secreted as VLDL -> adipose tissues
- cholesterol and bile salts synthesis
fasting state
- fatty acids (released from adipose tissues and transported to liver) -> acetyl CoA -> ketone bodies, exported to provide fuel for other tissues
what does the liver detoxify
foreign compounds (xenobiotics)
- alcohol, medications
endogenous compounds
- bilirubin
what is cori cycle
- interaction between liver and muscle to handle lactate (during anaerobic respiration)
describe cori cycle
In muscle
- glucose -> pyruvate -> lactate
In liver
- lactate -> pyruvate -> glucose (via gluconeogenesis)
what is glucose-alanine cycle
- interaction between liver and muscle to handle amino acids (produced by activity in muscles)
describe glucose-alanine cycle
In muscle
- glucose -> pyruvate -> alanine (process: TRANSAMINATION -> requires conversion of a-amino acid to a-ketoacid for process to occur)
In liver
- alanine -> pyruvate (with release of NH4+) -> glucose (via gluconeogenesis)
*NH4+ converted to urea and excreted
liver function tests:
- albumin
- coagulation tests for clotting factors (synthesized by liver)
- alanine aminotransferase/ aspartate amino transferase -> present in hepatocytes -> cirrhosis causes release of enzyme thus higher levels in blood
- alkaline phosphatase -> concentrated in bile ducts -> obstructive issues in biliary system -> increase alkaline phosphatase
- Y-glutamyltransferase (GGT) -> release from damage to biliary ductal cells
