Investigation of Disease Lectures 7-9 Flashcards
How much does the liver weigh in adults?
Approx 1500-1600 grams
Largest organ
What are some functions of the liver?
1) Gluconeogenesis/glycogen synthesis
2) Steroid catabolism, lipid metabolism, cholesterol and lipoprotein synthesis
3) Deamination
4) Bilirubin excretion
5) Bile salt production
6) Synthesis of coagulation factors
7) Vitamin (A, B12) and iron storage
Describe the blood flow between the liver and the heart
Hepatic artery into liver (25% of input)
Hepatic portal vein into liver (75% of input)
Hepatic vein from liver to inferior vena cava into heart
Briefly describe the structure of the liver
Liver lobules are functional units formed by hepatic plates
- middle of each is a central vein
- edge of each is portal triad (Bile duct, portal vein and hepatic artery)
- Bile canaliculus collects bile produced by hepatocytes and moves it to bile duct
Describe the process of bilirubin synthesis
- Erythrocytes destroyed in spleen
- Haemoglobin released
- Separated to haem and globin
- Haem to biliverdin by haem oxygenase
- Biliverdin to Bilirubin by biliverdin reductase
What colour is bilirubin and how is it carried in the blood?
Yellow
Carried in blood conjugated to albumin
Where, why and how is bilirubin conjugated?
Where? In the liver
Why? To render it more soluble
How? By the addition of glucuronic acid by uridine diphoshogluconate (UDP) glucuronosyl transferase
What happens to bilirubin after it is conjugated in the liver?
Secreted into first into the gall bladder, then into the bile duct for excretion into the intestine
What are the direct and indirect measurements of bilirubin and how are they performed?
Direct measures conjugated bilirubin
Indirect measures unconjugated bilirubin
Van den Bergh reaction measures conjugated bilirubin: React bilirubin with diazotised sulphanilic acid to give purple coloured azobilirubin that absorbs at 600nm
- Addition of caffeine breaks intramolecular hydrogen bonding in unconjugated bilirubin allowing it to react
What are the 4 fractions of bilirubin found in plasma?
1) Unconjugated (alpha)
2) Monoglucuronide conjugated (beta)
3) Diglucuronide conjugated (gamma)
4) Bilirubin covalently bound to albumin (delta)
What happens to bilirubin in the intestines?
Reduced by bacteria to Urobilinogen
- Most urobilinogen reabsorbed by portal vein to kidney and liver
> Urobilinogen in intestine converted first to stercobilinogen and then oxidised to stercobilin (brown)
How is urobilinogen detected in urine?
Reaction with Ehrlich’s reagent
- Degree of colour change (dark pink to red) is proportional to amount of urobilinogen
What is jaundice and whn does it occur?
Yellow pigmentation of skin, sclera (whites of eyes) and mucosa
- occurs when plasma bilirubin exceeds ~ 30-50 µmol/L (normal
What are the main causes of unconjugated hyperbilirubinemia and give examples
Increased bilirubin production > Hemolysis > Erythrocyte abnormality > Ineffective erythropoiesis (red blood cell production) Decreased hepatic bilirubin clearance > Fasting > Gilberts syndrome > Crigler-Naijar syndromes
What are the main causes of conjugated hyperbilirubinemia and give examples
Intrahepatic disorder >Hepatocellular disease of any cause > Cholestatic disease of any cause > Dubin-Johnson syndrome > Rotor syndrome Extrahepatic disorder > Biliary tarct pathology > Pancreatic pathology
What is Gilbert’s Syndrome?
- Autosomal dominant
- Decreased uptake of bilirubin and decreased conjugation
- Mild unconjucated hyperbilirubinaemia
What are Crigler-Naijer syndromes types 1 and 2?
Type 1:
- Autosomal recessive
- absense of UDPG transferase
- severe unconjugated hyperbilirubinaemia
- lethal
Type 2:
Autosomal recessive
Partial defect
What is Dubin-Johnsom syndrome?
- AR
- Decreased hepatic excretion of bilirubin
- mild conjugated hyperbilirubinaemia
What is Rotor syndrome?
- AR
- similar to D-J but no hepatic pigmentation
What is the typical profile of a liver function test (LFTs)
- Albumin
- Bilirubin (total and conjugated)
- Transaminases (alanine and aspartate)
- Alkaline phosphatase
- Gamma-glutamyl transferase
What are some other LFTs
- Prothrombin time (PT)
- Urinary bilirubin
- Urobilinogen
What are the 2 transamines that are measured in the LFT?
Alanine aminotransferase (ALT) Aspartate aminotransferase (AST)
High levels of ALT and/or AST indicate what about the liver?
Indicate liver disease due to heptocellular intergrity Causes include: Infective agents Autoimmune disorders Toxins
Is ALT or AST better for measuring liver function and explain why?
ALT more specific than AST
- ALT is cytoplasmic and so is more easily released into plasma than AST (cytoplasmic and mitochondrial)
What are the 2 biliary tract enzymes measured in LFTs?
Alkaline phosphatase (ALP) Gamma-glutamyl transferase (yGT)
What is the main cause of increased ALP and yGT in the plasma?
Cholestasis (obstruction of bile from the liver to small intestine)
Why are ALP and yGT raised in cholestasis?
Usually anchored to biliary canalicular and sinusoidal membranes
- In cholestasis these enzymes are rendered soluble
What other factors can cause an increase in plasma yGT?
Alcohol abuse: - >10 upper limit of normal Enzyme inducing drugs: - Phenytoin - Rifampicin Weight: - 50% higher yGT in patients with BMI >30
List some possible causes of Early Jaundice (
Haemolysis: - blood group incompatibility between mother and baby (commonest) - red cell membrane defects G6PD deficiency Pyruvate kinase deficiency Infection Genetic defects of bilirubin metabolism
What are some characteristics of physiological jaundice in babies (>48 hours)
- 30 to 70% affected
- Total bilirubin usually
What things can exacerbate physiological jaundice?
- Prematurity
- Dehydration
- Haemolysis
- injections
- Hypoglycemia
- Hypothyroidism
- Inadequate calorie intake
- Intestinal obstruction
Describe the causes and tests of prolonged jaundice (>14 days) caused by CONJUGATED bilirubin
- alpha1-antitrypsin deficiency (alphaAT concentration)
- Galactosaemia (red cell glalactose-1P-uridyltransferase)
- Cystic fibrosis (sweat test)
- Biliary atresia (pale stools)
- Dubin-Johnson and Rotor syndromes
Describe the causes and tests of prolonged jaundice (>14 days) caused by UNCONJUGATED bilirubin
- Breast milk jaundice (benign condition)
- G6PD deficiency
- Congenital hypothyroidism
- Crigler-Najjar syndrome
Describe the causes and LFT changes of acute & chronic hepatitis
Causes: - Hepatitis virus - Alcohol - Drugs/toxins - Cytomegalovirus - Autoimmune LFT changes: - Increased heptocellular enzymes (ALT, AST) - Mixed hyperbilirubinaemia - Urine bilirubin +ve - Increased PT time
Describe the causes and LFT changes of Cirrhosis
Causes: - Chronic alcohol abuse - Chronic hepatitis - Primary bilirary cirrhosis - Wilson's disease - Haemochromatosis LFT changes: - Reduced albumin, gamma/beta bridging - Normal or increased ALT, AST - Normal or mixed hyperbilirubinaemia - Increased PT time
Describe the causes and LFT changes of Cholestasis
Causes:
- Gallstones
- Malignancies (pancreas)
- Bile duct stricture (narrowing of ducts)
- Biliary atresia (congenital absense or closure of bile ducts)
LFT changes:
- Increased biliary tract enzymes (ALP, yGT)
- Conjugated hyperbilirubinaemia
- Urine bilirubin +ve
- Decreased urine urobilinogen
What is the prevalence of autoimmune hepatitis, how is it tested for and diagnosed and how is it treated?
- 1 in 10,000
- Positive for autoantibodies
- Conformation by liver biopsy
- Managed with prednisolone and azathioprine
What is primary biliary cirrhosis?
- Autoimmune disease
- common in middle-old aged women
- Positive for mitochondrial antibodies
What does IMD stand for?
Inherited metabolic disorder
What is the name of the screening programme run in the UK?
NHS newborn blood spot (NBS) screening programme
What disorders does the NHS NBS screening programme test for?
Congenital hypothyroidism Sickle cell disorders Cystic fibrosis IMDs: - Phenylketonuria - Medium chain acyl CoA dehydrogenase deficiency (MCADD) - Maple syrup urine disease (MSUD) - Isovaleric acidaemia - Glutaric aciduria type 1 - Homocystinuria
What is the cause and what are the symptoms of downs syndrome?
Phenotypic expression of trisomy 21
- severe learning difficulties
- short stature
- increased prevalence of congenital heart disease, hypothyroidism, leukemia and infections
When is downs syndrome screened for?
Fetal
What government body implements the newborn blood spot screening programme?
The UK National Screening Committee
What are the criteria for a screening programme in regards to the condition, the test, the treatment and the programme?
The condition:
- important health problem
- natural history and epidemiology should be understood
- latent pre-symptomatic phase
The test:
- Simple, safe, precise, validated, acceptable to general population
- Agreed policy for diagnostic follow up of screen positive cases
The treatment:
- Effective
- Evidence that treatment leads to improved outcome
The programme:
- Benefits outway harm
- value for money
- QA
How is the blood spot test performed?
- Heel is pin pricked and either:
- Collected and released onto spots on card
- Spotted onto card directly from heel
Card is called a Guthrie Card
What is the mode of inheritance of PKU and What is its disease and carrier prevalence ?
Autosomal recessive disorder
Incidence 1 in 10-12,000
Carrier frequency 1 in 50
What causes PKU?
Accumulation of phenylalanine as a result of a deficiency in phenylalanine dehydrogenase (PAH) that usually converts phenylalanine into tyrosine
What dietary chemical should PKU sufferers stay away from and why?
Aspartame
Because it is a dipeptide of phenylalanine and aspartate
What does the spectrum of PKU severity depend on??
Degree of enzyme activity
300 mutations identified (chromosome 12)
What blood phenylalanine concentration is associated with hyperphenylalaninaemia?
> 120µmol/L
What are the symptoms of untreated children with PKU and how it is diagnosed?
- Severe intellectual impairment
- Microcephaly (small head)
- Hypopigmentation
- Autistic behaviour
- Spasticity
Diagnosed by elevated phenylalanine in blood and detection of phenylketones in urine
- however most diagnosed by newborn screening
How does excess phenylalanine cause brain problems?
- Phenylalanine is a large neutral amino acid (LNAA)
- LNAAs compete for transport across blood brain barrier via large neutral AA transporter (LNAAT)
- Transporter saturated with PA
- Leads to decreased levels of other essential LNAAs in brain
- Reduced neurotransmitter and protein synthesis
- Hinders brain development
What is the cause of hypopigmentation in PKU?
extra reading
Less tyrosine being produced = less melanin production
How is phenylalanine measured?
- Ferric chloride
- Guthrie microbial assay (blood spot test):
> Bacillus subtilis grown on plate and inhibited by B-2-thienylalanine
> presence of phenylalanine alows growth to continue - Paper or thin layer chromatography
- Tandem mass spec
What causes congenital hypothyroidism?
Thyroid gland unable to produce thyroxine (T4)
- Results in overproduction of thyroid stimulating hormone (TSH) from anterior pituitary to try and stimulate thyroid to produce more thyroxine
What is the diagnostic TSH concentration in babies?
In excess of 200mU/L (milliunits/L)
Normal
What are the symptoms of infant congenital hypothyroidism?
Difficulty feeding
Sleepiness
jaundice
constipation
How is congenital hypothyroidism treated?
Oral administration of thyroxidine (liquid or tablet)
10µg/kg gradually increased until 12 yo
100 - 200µg/day thereafter
What is the prevelence of congenital hypothyroidism in the UK?
1 in 3000 babies born
What is the composition of normal adult haemoglobin (HbA)
2alpha and 2 beta polypeptide chains
What causes sickle cell disease?
Abnormality in haemoglobin molecule caused by an amino acid change in the beta chain
- This haemoglobin is called HbS
HbS homozygous individuals have sickle cell disease
What is the prevalence of sickle cell disease?
1 in 2000 babies born in UK
What are the symptoms of sickle cell disease?
- Anemia
- Attacks of severe pain
- Severe infections
How are the different haemoglobins in SCD examined?
Following seperation by HPLC or isoelectric focusing
What is the name of another inherited disorder that effects haemoglobin chain structure?
Thalassaemias
alpha and beta
What is the prevalence of cystic fibrosis and how is it inherited?
Most common single gene disorder in caucasian population - 1 in 2,500 Autosomal recessive (1 in 25 are carriers)
What causes cystic fibrosis?
- Mutations in the cystic fibrosis transmembrane conductance regulator gene (CFTR) on
chromosome 7 - deltaF508 mutation in CFTR gene accounts for more then 75% of CF
Defective CFTR = defect of chloride transport across membranes, producing excessively viscous mucous
What are the symptoms of CF?
- Recurrent lower respiratory tract infections
- pancreatic insufficiency
- high sweat chloride
- male infertility
What does the blood spot test test for in relation to CF? what are some other tests?
Blood spot test measures immunoreactive trypsin
- Also, DNA testing for mutations in CFTR gene
- Sweat test
Name some ways in which CF is treated
- Airway clearing techniques: > active cycle of breathing techniques (ACBT) > autogenic drainage > modified posture drainage > airway cleaning devices > Ivacaftor - helps to reduce mucus > Dornase alfa - helps to thin mucus - Administration of pancreatic enzymes - Antibiotics for chest infections In severe cases, lung transplant
What is the mode of inheritance and prevalence of medium chain acyl CoA dehydrogenase deficiency (MCADD)?
Autosomal recessive
1 in 8,000 babies born in the UK
What is the role of medium chain acyl CoA dehydrogenase in the body?
Enzyme that causes dehydrogenation of fatty acyl CoA’s (fatty acids) with a carbon chain of C6-C10 in beta oxidation of fatty acids
What occurs in MCADD?
Deficiency in MCAD
No or less beta oxidation
Accumulation of acyl CoA esters within the mitochondria and corresponding L-carnitine inside and outside mitochondria
What do MCADD patients commonly present with?
- present with hypoglycemia as product of beta oxidation is acetyl CoA which is used in glycolysis
- Low conc of plasma and urine ketones (acetyl CoA –> ketones and CO2)
- high plasma free fatty acids (3-hydroxybutyrate)
What are the symptoms of MCADD?
Fatigue vomiting sweating rapid breathing seizures
How is MCADD diagnosed?
Blood spot test
- measurement of octanoyl carnitine in blood spots by tandem mass spectrometry
What is the structure of a fatty acid?
Carbon chain with a carboxylic acid group on the end
What is the difference between saturated and unsaturated fatty acids?
Saturated have no double bonds - fully saturated with hydrogen
Unsaturated do have double bonds
What is the difference between cis and trans unsaturated fatty acids?
Cis (Oleic acid):
Natural conformation in body
Hydrogen atoms on same side of double bond
Trans (Elaidic acid):
Not part of normal metabolism, harmful
Hydrogens on opposite side to double bond
What is a polyunsaturated fatty acid?
A fatty acid with multiple double bonds
What is the structure of triacylglycerols?
3 carbon atoms of glycerol as backbone, esterified with 3 FA residues
- Carbons of glycerol labelled Sn1, Sn2 and Sn3
- Sn2 carbon esterified to unsaturated FA
Where are triacylglycerols stored and how are they used for energy?
Stored in adipocyte within a lipid droplet coated with perilipin
(adipose tissue)
- When stimulated by GH, glucagon (fasting hormones), hormone sensitive lipase (HSL) converts triacylglycerol into free fatty acids that can be used in beta oxidation
What are phospholipids used for?
Main lipid used in biological membranes (around 40-50%)
What are the main roles of cholesterol?
- Precursor of steroid hormones
- precursor of vitamin D
- Precursor of bile acids/salts
- Key component of biological membranes
What are the 2 types of cholesterol?
1) Free cholesterol
2) Esterified cholesterol (esterified to a FA)
How is dietary cholesterol transported from the intestinal lumen (duodenum and jejunum) to the blood?
- CEs hydrolysed to FC which is absorbed into micelles along with plant sterols and moved into intestinal cell by Niemann-Pick C1 like 1 protein (NPC1L1)
- Plant sterols returned to lumen by sterol transporter
- FC esterified back to CEs
- CEs, triacylglycerols and apoB48 delivered to extracellular fluid in chylomicrons by microsomal transport protein
- Mature chylomycrons delivered to blood
How are lipoproteins formed?
Water insoluble Lipids associate with apoproteins to form water soluble lipoproteins
What are the main 3 types of apoproteins?
A, B and C - referred to as apoA, apoB and apoC
How are lipoproteins classified and what are the 5 classes?
Classified according to their density From low to high density: Chylomicrons Very low density Intermediate density low density high density
What are the functions of the main 4 lipoproteins (chylomicrons, VLDL, LDL and HDL) and which apolipoproteins are involved in each?
Chylomicrons: - B48, A-I, C-II, E - largest lipoprotein - synthesised in intestine after meal - Main carrier of dietry triglyceride VLDL: - B100, C-II, E - Synthesised in liver - Main carrier of endogenously produced triglyceride LDL: - B100 - Generated from VLDL in the circulation - Main carrier of cholesterol HDL: - A-I and A-II - Smallest - Protective function - Takes cholesterol from extrahepatic tissues to liver for excretion
What are the roles of apoC and apocE in chylomicrons?
The apocC components play a role in activating lipase on endothelial surfaces, but also masks recognition of apoE by liver uptake cells
- As facts are stripped out of the particles (lipoproteins) cholesterol is concentrated and the apocC proteins shed so that apoE becomes exposed
Which areas of the HDL interact with cholesterol?
The 2 apolipoprotein A-I chains
What is the difference between an atheroma and atherosclerosis?
Atheroma - accumulation of lipid that occur on the inner lining of the arteries
Atherosclerosis - narrowing and hardening of the artheries (caused by an atheroma)
Describe the process of atheroma formation leading to atherosclerosis
1) Fatty streak
- LDL accumulates in extracellular space between endothelial and connective tissue layers and is oxidised
- Phospholipase A2 can caused damage to LDL particles, promoting their uptake onto macrophages by scavenger receptors –> macrophages become foam cells
- Smooth muscle cells divide and take up cholesterol - initiated by paracrine factors released from macrophages
2) Stable fibrous plaque
- Lipid core accumulates
- Fibrous scar tissue forms over lipid core
- Proliferation of smooth muscle cells thickens wall
- Dying cells in fatty deposits replaced by scar tissue and become calcified
3) Vulnerable plaque
- Converted into vulnerable plaque by degradation of fibrous cap to thin cap by macrophage enzymes
- Rupture in plaques exposes platelets to collagen and initiates blood clot (thrombus)
How are both cholesterol and triacylglycerols measured in the lab?
- Both reacted with water in automated analysers with multiple enzymatic steps
- give coloured products
- Cholesterol = 1 H20, 3 enzymatic steps synthesis
- Triacylglycerol = 3H20, 4 enzymatic steps
How is hypercholesterolaemia treated?
Lifestyle changes:
- No smoking
- Maintain healthy weight
- Less than 30% fat diet, with less than 10% of total being saturated.
Drug treatments:
Statins - inhibit HMG CoA reductase that catalyses conversion of hydroxymethylglutaryl CoA (HMG-CoA) to Mevalonate in de novo synthesis of cholesterol
Squalene synthetase inhibitors - inhibits squalene synthetase that catalyses conversion of presqualene pyrophospahte to squalene
What are the healthy levels of blood total cholesterol, LDL, HDL and Triglycerides for adults and those at risk
Healthy adults:
Total cholesterol -
