Liver physio

Question 1

functions of liver

Answer 1

• 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

Question 2

what do liver metabolise

Answer 2

• nutrients (carbohydrates, lipids, protein)
• toxin & drugs (detoxification)

*maintains energy homeostasis (produce energy when needed)

Question 3

uses of energy produced by liver

Answer 3

• heat production
• muscle activity
• secretion
• membrane potential
• synthesis of materials
• absorption of food

Question 4

organs involved in fuel homeostasis

Answer 4

• liver
• adipose tissue
• skeletal muscles

Question 5

how do liver and adipose tissue communicate for fuel homeostasis

Answer 5

• fatty acids from liver -> stored in adipocyte via VLDL
• glucose from blood can also be stored as fatty acids in adipocyte

Question 6

how do liver and muscles communicate for fuel homeostasis

Answer 6

• amino acids can be either used by muscles to make protein or used by liver to make protein/ glucose

Question 7

how do adipose tissue and muscle communicate in fuel homeostasis

Answer 7

• glucose usage: glucose can be used to create fatty acids in adipose tissue OR broken down in muscles to release energy

Question 8

metabolic function of liver

Answer 8

• body’s central metabolic clearing house -> ensure appropriate level of fuel is available to brain, organs etc

Question 9

why is liver able to be in charge of body’s metabolism

Answer 9

first pass effect
- all nutrients absorbed by intestines (except fatty acid in lymphatic system) are released to portal vein -> liver

Question 10

what does the liver do during fasting

Answer 10

• activate glycogen and ketone bodies (longer lasting source of fuel)

Question 11

what happens to glucose after entering liver via portal vein

Answer 11

• converted to glucose 6-phosphate
• can be stored as glycogen via a series of steps (and vice versa when glucose is needed)

Question 12

what happens when the body requires energy

Answer 12

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

Question 13

what is gluconeogenesis

Answer 13

process by liver (convert other substances to glucose)
- amino acids/ lactate -> converted to pyruvate -> converted to glucose 6-phosphate

Question 14

how does liver maintain glucose levels during fed & fasting states

Answer 14

*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

Question 15

what happens to amino acids when absorbed from portal vein (4)

Answer 15

• 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

Question 16

how are nucleotides (nucleic acid) metabolised

Answer 16

nucleic acid excretion (similar to deamination)
- nucleic acid -> ammonia -> urea cycle to form urea

SYNTHESIS/ SALVAGING of ribonucleotides & deoxyribonucleotides occur in liver

Question 17

what happens to fat that reaches the liver via lymphatic system

Answer 17

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

Question 18

what happens to liver fatty acid metabolism during fed & fasting states

Answer 18

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

Question 19

what does the liver detoxify

Answer 19

foreign compounds (xenobiotics)
- alcohol, medications

endogenous compounds
- bilirubin

Question 20

what is cori cycle

Answer 20

• interaction between liver and muscle to handle lactate (during anaerobic respiration)

Question 21

describe cori cycle

Answer 21

In muscle
- glucose -> pyruvate -> lactate

In liver
- lactate -> pyruvate -> glucose (via gluconeogenesis)

Question 22

what is glucose-alanine cycle

Answer 22

• interaction between liver and muscle to handle amino acids (produced by activity in muscles)

Question 23

describe glucose-alanine cycle

Answer 23

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

Question 24

liver function tests:

Answer 24

• 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