PBL 5 Flashcards
The end product of glycolysis is different in aerobic and anaerobic conditions, what are these?
Aerobic - pyruvate produced
Anaerobic - lactate produced
How does glucose enter hepatocytes?
Via facilitated diffusion through the GLUT-2 transporter
How is glucose ‘trapped’ when it first enters hepatocytes?
It is converted to glucose-6-phosphate by hexokinase, this phosphorylation traps glucose in the hepatocytes
What reaction does hexokinase catalyse?
Conversion of glucose to glucose-6-phosphate
How does hexokinase IV differ in activity to hexokinase I-III?
Hexokinase I-III: activated at very low concentrations of glucose, and is a relatively slow enzyme
Hexokinase IV: only activated which glucose levels are high, but the speed of the enzyme is much higher. It increases in activity as the concentration of glucose increases
What is the rate limiting step in glycolysis?
The conversion of fructose-6-phosphate to fructose 1,6-bis-phosphate by phosphofructokinase 1 (PFK-1)
What is known as the point of no return in glycolysis and why?
The conversion of fructose-6-phosphate to fructose 1,6-bis-phosphate by phosphofructokinase 1 (PFK-1)
This reaction is irreversible
How is the enzyme phosphofructokinase 1 (PFK-1) regulated?
Activated by AMP and fructose 2, 6 bisphosphate
Inhibited by ATP and citrate
What reaction in glycolysis does PFK-2 regulate?
How?
The conversion of fructose-6-phosphate to fructose 1,6-bis-phosphate by phosphofructokinase 1 (PFK-1)
It regulates the activation of fructose 2,6-P, which is an activator on this reaction
How is the activity of PFK-2 regulated by glucagon?
How does this effect glycolysis?
Glucagon binds to hepatocytes causing cAMP signalling
This activates PKA which phosphorylates PFK-2
Phosphorylated PFK-2 is inactive
PFK-2 cannot stimulate fructose,2,6-P
Fructose 2,6-P cannot stimulate the action of PFK-1
This inhibits glycolysis, and stimulates Gluconeogenesis
How is the activity of PFK-2 regulated by insulin?
How does this effect glycolysis?
High insulin inhibits glucagon signalling
This means PFK-2 cannot be phosphorylated
Unphosphorylated PFK-2 is active
Active PFK-2 stimulates fructose,2,6-P
Fructose 2,6-P can then stimulate the action of PFK-1
This causes increased glycolysis
How many ATP are generated in glycolysis?
2 ATP
How is glucose converted to glycogen?
Glucose-6-phosphate converted to glucose 1-phosphate by phosphoglucomutatase
Glucose 1-phosphate converted to glycogen by glycogen synthase
How is glycogenesis regulated by glucagon?
Glucagon activates cAMP signalling which activates PKA
PKA phosphorylates glycogen synthase (branching enzyme) causing it to become inactive
This results in decreased glycogenesis
How does glucagon regulate glycogenolysis
Glucagon activates cAMP signalling which activates PKA
PKA phosphorylates glycogen phosphorylase (a debranhing enzyme) causing it to become active
This increases glycogenolysis
What happens when glycogen synthase is phosphorylated?
It becomes inactive
Glycogenesis is inhibited
What happens when glycogen phosphorylase is phosphorylated?
It becomes active
Glycogenolysis is activated
How does glucagon regulate Gluconeogenesis?
Represses pyruvate kinase - increasing the amount of PEP
Increasing expression of PEP carboxykinase - increasing PEP
Repressing F-2,6-BP by PFK-2: represses glycolysis
What cycle is pyruvate fed into following glycolysis?
The TCA cycle
How are express carbohydrates and proteins stored in the body?
As fatty acids (triacylglycerols) in adipocytes
What is the rate limiting step of fatty acid synthesis?
Conversion of acetyl-coA to malonyl-coA by acetyl co A carboxylase (ACC)
How is the conversion of acetyl-coA to malonyl-coA by acetyl co A carboxylase (ACC) regulated?
Activated by citrate
Inhibited by fatty acyl-CoA: negative feedback mechanism
Inhibited by glucagon: causes phosphorylation of ACC
Activated by insulin: inhibits glucagon
Through what process can energy be derived from stored fats in the presence of oxygen?
Beta oxidation
What compound are fatty acids most likely to be stored as?
Palmitoyl CoA (16 carbon chains)
How can energy be derived from stored fats in the absence of oxygen?
Through the production of ketone bodies
What are the two main ketone bodies?
Acetoacetate
3-hydroxybutyrate
Why can you get ketoacidosis in type I diabetes?
Absence of insulin, so glucagon cannot be suppressed
You get fasting signals despite being well fed
Fasting signals promote ketone body production for energy
Ketone bodes are highly acidic
What is the only nutrient that cannot be stored in the liver?
Protein - it has no storage form
Some amino acids are fed into ketone body production. They are either partially or fully ketogenic. Which amino acids are these?
Partially ketogenic - Phe, Try, Trp
Fully ketogenic - Leu, Lys
What reaction does alanine transaminase (ALT) catalyse?
Conversion of:
alanine + alpha-ketoglutamic acid > pyruvate + glutamate
ALSO DOES REVERSE REACTION
What reaction does aspartate transaminase (AST) catalyse?
Conversion of:
Aspartate + alpha-ketogenic acid > oxaloacetate + glutamate
ALSO DOES REVERSE REACTION
Compare ALT and AST and their specificity and amounts they are found in the liver?
ALT: more specific to the liver, found in small amounts
AST: less specific to the liver, found in large amounts
How is does peripheral excess ammonia get fed into the urea cycle
Excess ammonia is put into glutamine which is transported to the liver
Glutamine is converted into glutamate
Glutamate conversion into alphaketoglutarate by AST gives off aspartate
Aspartate is fed into the urea cycle
What does it mean if a drug has a small or large volume distribution?
Small volume distribution - drug tends to stay in bloodstream bound to plasma proteins, so is not widely distributed in the body
Large volume distribution - drug is more widely distributed in the body and is not bound to plasma proteins. Drug is probably more lipid soluble
What are the two phases of drug metabolism?
Phase I - functionalisation
Phase II - conjugation
What is the aim of drug metabolism?
To convert a drug from a lipid soluble to a water soluble form so it can be excreted in urine
What happens in phase I metabolism?
A drug is metabolised to produce or uncover a chemically reactive functional groups
At what stage of metabolism are pro drugs activated?
Phase I (functionalisation)
What are the most prominent enzymes of phase I metabolism?
Cytochrome p450
What happens in phase II metabolism
A drug is conjugated to make it more water soluble and easier to excrete
What is the role of the liver in the recirculating of some drugs?
Enterohepatic circulation
- Addition of glucuronide to a drug by glucuronyl transferase in the liver
- This is excreted in bile and into the GI tract
- hydrolysis by beta-glucuronidase in the GI tract causes it to be reabsorbed
Through what process can the liver extend the half life of a drug?
Enterohepatic circulation
Which drugs are particularly susceptible to enterohepatic circulation?
Oestrogens
Rifampicin
Chloramphenicol
Morphine
How does metabolism enzyme activity alter with age?
As you get older, it decreases, so may need to give lower dosages
Why does drug metabolism increase during pregnancy?
Increased blood flow to kidneys and liver
Increased expression of metabolic enzymes
What is the difference between a type A and type B adverse drug reaction?
Type A - exaggerated response to a drugs normal actions when given at a usual dose
Type B - a bizzare reaction to a drug that was not expected upon known pharmalogical actions of the drug
How can cigarette smoking and alcohol effect drug metabolism?
It increases the metabolism of many drugs
Name some dietary factors that effect metabolism
Metabolism inducers - BBQ meat, Brussels sprouts
Metabolism inhibitors - grapefruit juice
What are the 3 types of liver toxicity?
Hepatocellular -
Cholestatic - bile obstruction
Mixed hepatocellular and cholestatic
What are the immune cells of the liver called?
Kupffer cells
What are bile acids synthesised from?
Cholesterol
How do bile acids become bile salts?
What are the different types of bile salts?
They are conjugated
BA-Z (conjugated with taurine and glycine)
BA-Y (conjugated with sulphate and glucuronate)
By what transporters are the different bile acids and bile salts secreted at the apical membrane into the canaliculi?
Bile salt export pump (BSEP) - secretes BA-Z and BA- (unconjugated bile acid)
Multidrug resistance associated protein 2 (MRP2) - secretes BA-Y
What family of transport proteins do the BSEP and MRP2 belong to?
ABC (ATP binding cassette) transporter family
How and where are bile acids reabsorbed in the intestines?
Unconjugated bile acids are reabsorbed all along the intestine in a passive manner
Conjugated bile acids are active reabsorbed in the terminal ileum
How are the different bile acids and salts taken up by hepatocytes once they are reabsorbed?
BAH - simple diffusion
BA- (unconjugated bile acid): exchanged for chloride (OATP)
BA-Z (conjugated bile acid): co transport with sodium (NTCP)
What is bilirubin?
It is a major end product of haemoglobin degradation - formed by the four pyrrole nuclei of heme
The colour is what gives bile its colour
How is bilirubin taken up by hepatocytes and excreted in the bile canaliculi?
Free bilirubin is taken up by OATP (organic anion transport polypeptide) into hepatocytes
Bilirubin is conjugated and transported into canaliculi by MRP2 (Multidrug resistance protein 2)
What is the fate of bilirubin once it enters the intestine?
Converted to urobilinogen - some of this is reabsorbed and excreted as urobilin (yellow) in urine
Some urobilinogen is converted into stercobilin (brown) - excreted in the feces
What makes urine yellow?
Urobilin
Why is bilirubin measured?
To assess liver function
What is bilirubin usually conjugated with in the liver?
Glucuronide
What is Jaundice a result of?
Excessive levels of serum bilirubin due a problem in the breakdown and excretion of bilirubin from the body
What are the 3 types of jaundice and what are they caused by?
Pre-hepatic: problem with breakdown of haemoglobin
Intra-hepatic: problem with breakdown of bilirubin in liver
Postheaptic: problem with excretion of bilirubin from bile duct
What is the pathogenesis of viral hepatitis?
Hepatitis infects hepatocytes in the liver
Antigen recognition of viruses by cytotoxic T cells
This results in destruction/apoptosis of hepatocytes
Why are younger patients less likely to have symptoms of hepatitis?
Their immune system is underdeveloped, therefore the immune response to viral infection is reduced
The symptoms are due to the immune response
What are the symptoms of hepatitis?
Fatigue Itching Nausea Jaundice Right upper quadrant pain and tenderness
How is hepatitis A spread?
Faecal-oral route
What family of viruses does Hep A belong to
Picornavirus
RNA virus
What type of hepatitis virus can occur due to indigestion of contaminated shellfish?
Hep A
What is the most common hepatitis virus?
Hep A
What is the pathophysiology of Hep A infection?
Replicates in liver
Acute infection
Tends to be self limiting and normally gets better in a couple of weeks
What is the serological course of antibodies following Hep A infection?
Acute infection: IgM antibodies for hep A
Recovery or vaccinated state: IgG antibodies for hep A
What is the vaccination called for hep A
Harvix
How is hep E transmitted?
Faeco-oral route
What type of virus is Hep E
Herpesvirus
RNA
What are the different genotypes for Hep E and where are they found?
Genotype 1,2: water borne
Genotype 3,4: zoonotic, associated with undercooked pork
What types of viral hepatitis can be spread by blood and bodily fluids?
B,C,D
Somewhat E
What type of virus is Hep B
DNA
How does the pathophysiology of hep B differ on the age of contraction of the virus?
If you are exposed early in life - this can lie dormant for some time and lead to a chronic infection
If you are exposed later in life - this can cause symptomatic infection
What is the course of hep B infection if exposed early in life?
Immune tolerant stage - virus sits there as immune system is underdeveloped
Immune clearance stage - immune system develops and tries to clear virus
Inactive carrier stage - virus becomes inactive
Reactivation - cycles of inflammation and repair occur, leading to fibrosis
What are the different viral proteins found in hep B diagnosis and what do they mean?
HBsAg (Hep B surface antigen) - this shows infection present
HBeAg (Hep B e antigen) - this shows virus is in a replicative state
What defines chronic hep B infection?
If surface hep b antigen (HBsAg) is present for more than 6 months
What are the host antibodies produced against Hep B infection?
Anti-Hbe - hepatitis B e antibody
Anti HBc (IgM, IgG) - hepatitis B core antibody
Anti HBs - hepatitis B surface antibody
What type of antibody will be present if you have been vaccinated against Hep B
Anti-HBs: hepatitis b surface antibody
What are the two approved NICE treatments for chronic Hep B infection?
Interferon (pegylated interferon)
Tenofovir/Entecavir
How does interferon work in Hep B treatment?
How effective is it?
Stimulates the immune system
Has low efficacy (less than 25% of people benefit)
However when it does work it works well
How do Tenofovir and Entecavir work in Hep B treatment?
Why are they lifelong treatments?
Act as nucleoside analogues which inhibit DNA polymerase
They cannot clear the cccDNA, therefore if you stop taking drugs then the virus will just return
What type of virus is Hepatitis Delta?
RNA
Which other hepatitis virus does hepatitis Delta require for replication?
Hepatitis B
What type of virus is Hepatitis C
RNA
Flavivirus
How likely is Hep C virus infection to become chronic?
25% clear virus
75% get the chronic infection
How is hepatitis C infection treated?
Direct acting antivirals (DAAs) - target enzymes in HCV life cycle
Ribavirin - nucleoside Inhibitor, prevents viral RNA synthesis
What kind of drug is sofosbuvir?
What is the mechanism of action?
It is a direct acting antiviral drug (DAA)
It inhibits the HCV NS5B RNA dependant RNA polymerase
How does cortisol effect glucose levels?
Increases glucose levels by inducing:
Gluconeogenesis
Lipolysis
Which hepatitis virus is associated with 20% mortality rate in pregnant women?
Hep E
How much bile is secreted each day?
250mL - 1000mL
