Topic 7: Kidney Function and Disease; Liver Function and Disease

What are the main functions of the kidneys?

excretion

• urea 

• creatinine

• uric acid

• uremic toxins

homeostasis 

• regulate electrolytes

• retention of bicarb, water, albumin, AA, glucose 

endocrine

• renin

• erythropoietin

• 1, 25 (OH)2 of vit D3

What hormones regulate the kidneys?

ADH - water reabsorption

aldosterone - sodium reabsorption

PTH - calcium reabsorption, PO4- excretion, 1 25 (OH)2-vit D3 synthesis

What conditions affect GFR?

• glomerulonephritis

• DM

• hypertension

• nephrotoxins 

how does proteinuria affect GFR and the kidneys?

reduced GFR and nephron loss (inflam and scarring in renal tubules

What is creatinine clearance (excretory capacity defined as?)? What is it used for? Where is creatinine derived from? What is clearance a function of?

• volume of plasma from which a given substance is removed by filtration during its passage through the kidney

• important indicator of renal health

• creatinine = byproduct of muscle metabolism that is excreted unchanged in urine 

• function of GFR and rate of secretion/reabsorption between peritubular capillaries and nephron 

What is GFR? What is the normal value? What is it corrected for? 

• volume of plasma from which a given substance is removed by filtration per unit of time 

• 140mL/min 

• corrected for BSA of 1.73m²

• 140mL/min/1.73m²

What is the equation to determine clearance? clearance of excreted molecule is = to GFR if?

clearance = (U x V)/P

U = urinary [X]

V = urine vol

P = plasma [X]

if it is freely filtered at glomerulus

glomerulus is sole route of excretion from body → no tubular secretion or reabsorption

non toxic and easily measured

What are the 2 types of renal diseases?

acute failure

• cessation of kidney function

• pre renal (failure of blood supply)

• renal (intrinsic)

• post renal (drainage obstructed)

chronic failure

• progressive irreversible kidney tissue destruction 

• symptomless until GFR <15mL/min/1.73²

• same parameters as acute but over extended period of time 

• glomerulonephritis

• DM

• hypertension

• nephrotoxins 

What molecules are measured for urinalysis

• glucose - DM

• bilirubin - conjugated, pathological

• urobilinogen - indicative

• ketones - FA metab, DM ketoacidosis

• specific gravity - urinary density

• pH - acidic, renal tubular acidosis 

• protein - abnormal excretion

• blood - malignancy, UTI

• nitrates - UTI

• WBC - inflam, UTI 

How would you investigate kidney disease? What would you measure?

• creatinine + urea

• GFR

• urinary protein

• electrolytes

How sensitive is creatinine and urea for assessing kidney function?

• convenient but insensitive measure of renal function

• GFR must fall to half before creatinine rises

• creatinine depends on age and body sizes

• urea is less useful as its affected by dietary protein, GI bleeding and urine flow

How is urea derived?

catabolism of protein + NA forms urea + ammonia

urea formed in liver by urea cycle enzymes

→ excreted thru kidney 

freely filtered at glomerulus and 40-70% reabsorbed 

What renal defects yield proteinuria?

• bence jones protein

• albuminuria

• beta 2 or alpha 1 microglobinuria

• Tamm-horsfall glycoprotein 

What is acute renal failure? What are the 3 main causes?

end stage kidney disease

cessation of kidney function

1. pre-renal: failure of blood supply to kidneys

   1. pre renal blockage i.e. tumour

2. renal: intrinsic dmg to kidneys

   1. glomerulonephritis/toxins

3. post-renal: impaired urinary drainage

   1. kidney stones or malignancy blocking ureter

How would you diagnose ARF? What are some causes

ID pre or post renal factors, other severe illness, drug history and time of onset

pre-renal

• decreased plasma volume, CO

• occlusion of renal artery

• biochemistry:

  • increased serum urea and creatinine 

  • metabolic acidosis 

  • hyperkalaemia

  • urine osmolality

renal

• determine blood loss, septic shock, glomerulonephritis, nephrotoxins, acute tubular necrosis

post renal

• kidney stones

• cancers 

• decreased glomerular filtration pressure through back pressure from blockage

What is chronic renal failure? How can it be treated and what symptoms are seen/when are symptoms seen?

progressive irreversible kidney tissue destruction 

treated by dialysis or transplantation

symptomless until GFR <15mL/min (~10%)

symptoms:

• reduced tubular H2O reabsorption - fluid and sodium dysregulation

• hyperkalaemia

• metabolic acidosis

• reduced 1,25 (OH)2-VD3 and dysregulated calcium and PO4- metabolism

• hypocalcaemia

• anaemia from EPO synth failure 

What are the functions of the liver?

• metabolism - carbs, lipid, protein

  • TCA cycle, AA synth, ox phosphorylation

  • turnover of RBC components

• secretory - bile, bile acids, salts, pigments

• excretory - bilirubin, drugs, toxins

• synthesis - albumin, coag factors

• storage - vitamins, carbs, lipids

• detox - toxins, ammonia

• extensive macrophage pop

What are some genetic causes of liver disease?

abnormal gene inherited can cause substance buildup in liver → dmg

Gilberts syndrome and Crigler-Najjar syndrome

• UGT1A1 gene mutations → decreased bilirubin UDP glucuronosyltransferase activity

• this prevents bilirubin conjugation (mild jaundice)

Dubie-Johnson syndrome

• mutation in canalicular multiple drug-resistance protein 2 (MRP2) resulting in mild increase in conjugated bilirubin 

Haemochromatosis 

• iron accumulation - liver toxicity

Hypooxaluria and oxalosis

• oxalate accum → kidney stones

Wilsons disease, Menkes disease

• copper accum - liver toxicity

Alpha 1 AT def

• reduced antiprotease → lung and liver dmg 

What viral infections cause liver disease?

Hepatitis A, B, C

Describe Hepatitis A. How is it transmitted? Who is affected? What is the recovery like? are there any treatments or vaccines?

• most common cause of acute viral hepatitis

• most frequent in children + young adults

• faceal-oral contact and occur as result of poor hygiene

• waterborne and food borne epidemics

• recovery usually complete 

• rarely fulminant hepatitis 

• vaccine available 

Describe Hepatitis B. How is it transmitted? What % patients become carriers/chronic hep B? What are the symptoms and how long does it last? Are there any treatments or vaccines?

• wide spectrum of liver disease - subclinical carriers to severe hepatitis/acute liver failure (fulminant)

• HBV transmitted parenterally by contamined blood/products

• 5-10% dev chronic hep B or become inactive carriers

• symptoms: anorexia, malaise, fever, nausea, vomiting, jaundice

• persist for weeks to 6 months

• supportive treatment/vaccine available

Describe Hepatitis C. How is it transmitted? What are the symptoms and how long does it last? What % show chronic hepatitis? How would you diagnose it? Are there any treatments or vaccines?

• transmitted parenterally by contaminated blood/products

• symptoms: anorexia, malaise, jaundice but can be asymptomatic

• fulminant hepatitis

• 75% become chronic hepatitis → cirrhosis and rarely hepatocellular carcinoma

• diagnosis: serologic + viral genome testing

• antiviral drug treatment: epclusa, harvoni, maviret, zapatier

• no vaccine

Describe the cholestatic causes of liver disease. 

reduction of stoppage of bile flow due to disorders of liver, bile duct, pancreas

• intrahepatic or extrahepatic origin

• accum of excess bilirubin causes jaundice

• skin + whites of eyes pigmented yellow, itchy skin, dark urine, light stools 

• lack of bile in intestine results in poor calcium uptake with reduced vit D leading to bone loss; poor absorption of vit K needed for blood clotting

• treatment depends on cause

What are the causes of intrahepatic cholestasis?

• acute hepatitis

• alcoholic liver disease

• primary biliary cholangitis with inflam and scarring of bile ducts

• cirrhosis due to HBV or HCV infection with inflam and scarring of bile ducts

• drugs

• cancer spread to the liver

What are the causes of extrahepatic cholestasis?

• gall stones in bile duct

• narrowing of bile duct

• cancer bile duct

• pancreatic cancer

• pancreatitis

What are the immune abnormalities causing liver disease?

• AI hepatitis

• primary biliary cirrhosis 

• primary sclerosing cholangitis 

What are the types of cancer causing liver disease?

• liver cancer

• bile duct cancer

• liver adenoma

What are other causes of liver disease?

• chronic alcohol abuse

• non alcoholic fatty liver disease

What are the risk factors for liver disease

• heavy alcohol use

• shared needles

• tattoos/body piercings

• blood transfusion before 1992

• exposure to blood/fluids

• unprotected sex

• exposure to chemicals and toxins

• DM

• obesity

Describe LFT. What are LFT useful in distinguishing?

measure plasma markers that are circumstantial indicators of liver function 

distinguish:

• biliary tract obstruction (cholestasis)

• acute hepatocellular dmg

• chronic liver disease

What are the clinical signs of liver disease?

• skin and eyes that appear yellowish (jaundice)

• abdominal pain and swelling

• swelling in legs and ankles

• itchy skin

• dark urine colour

• pale stool colour, or bloody or tar-coloured stool

• chronic fatigue

• nausea or vomiting

• loss of appetite

• tendency to bruise easily

What are some indicators of liver damage from POCTs

• increased urinary bilirubin: from biliary obstruction/hepatitis 

  • early indicator

• increased urinary urobilinogen

  • intestinal metabolism of bilirubin generates colourless urobilinogen 

  • 50% reabsorbed and transported to liver and excreted by kidney

  • hepatitis inhibits liver urobilinogen metabolism 

• INR

  • liver disease reduces synthesis of liver proteins: coagulation factors (7)

  • INR prothrombin time correlates with decreased factor production

Which markers are affected during liver disease and how is this seen in LFTs?

• increased serum bilirubin (total and conjugated)

  • early indicator

• increased hepatic intracellular enzymes in serum

  • hepatocellular dmg: AST, ALT

  • cholestasis: ALP, GGT

• decreased serum albumin 

  • liver disease reduces hepatocyte production of proteins 

What is the haem recovery pathway?

• old or damaged RBC are phagocytosed by macrophages in spleen

• iron is recovered by macrophages from haem

• then haem degraded to bilirubin

  • adults make 450 umol/day

• unconjugated bilirubin is released into portal circulation

  • water insoluble and bound to albumin

What are the two states of plasma biliirubin?

unconjugated (95%)

• water insoluble, bound to albumin 

• indirect since it requires accelerator for diazo reaction

conjugated (5%)

• water soluble

• appear in urine if bilirubin levels are elevated

• direct since it does not require accelerator for diazo reaction 

What are the urinary bile pigments?

• urobilinogen

  • normally small amounts 

  • increased in liver disease due to inability to excrete small amounts reabsorbed from gut 

  • decreased in cholestasis 

• bilirubin

  • appears in urine when plasma conjugated bilirubin rises

What is jaundice?

yellow staining of integument, sclerae, and deeper tissues and of excretions with bile pigments which are increased in plasma 

• is a symptoms of various disorders

medically charactererised as:

• yellowing of skin or whites of eyes resulting from: 

  • excess circulating bilirubin 

  • obstruction of bile duct, liver disease, or XS RBC breakdown 

Describe pre-hepatic jaundice. What type of jaundice is it and how does it arise? What does it cause

haemolytic jaundice

liver disorder resulting from increased bilirubin from Hb as a result of any process:

• toxins

• genetic

• immune

causes increased RBC destruction

Describe intra-hepatic jaundice. What type of jaundice is it and how does it arise?

hepatocellular

liver disorder resulting from:

• injury

• inflam

• failure of hepatic cell function 

often assoc with hepatitis, drugs and toxins

Describe post-hepatic jaundice. What type of jaundice is it and how does it arise?

cholestatic jaundice

liver disorder produced by inspissated (thickened) bile or bile plugs in small biliary passages in liver 

diminish or stop flow of bile

How would you distinguish pre, intra and post hepatic jaundice?

Pre

• bilirubin <75umol/L

• no bilirubin in urine

• increased LDH

• decreased Hb

• reticulocytosis 

Intra

• bilirubin increased late

• bilirubin in urine

• significant AST and ALT

• ALP increased late

Post

• marked bilirubin

• bilirubin in urine

• moderate AST, ALT, LDH

• ALP >3x upper limit of RR

• GGT increased

What liver enzymes are released following injury

• alanine aminotransferase (ALT)

• aspartate aminotransferase (AST)

• alkaline phosphatase (ALP)

• gamma-glutamyl transferase (GGT)

Describe alanine aminotransferase (ALT). Where is it found and what does it catalyse? Significantly elevated levels indicate:

• cytosolic enzyme found in liver parenchymal cells

• L-glutamate + pyruvate ←→ alpha-ketoglutarate + L-alanine 

• high levels indicate:

  • viral hep

  • DM

  • congestive HF

  • liver dmg

  • bile duct diseaese

  • IM

  • myopathy

  • strenous exercise 

Describe aspartate aminotransferase (AST). Where is it found and what does it catalyse? Significantly elevated levels indicate:

• cytosolic enzyme found in liver, heart, skeletal muscle, kidney, brain, RBC

• aspartate + alpha-ketoglutarate ←→ oxaloacetate + glutamate 

• elevated in:

  • myocardial infection

  • acute pancreatitis

  • AHA

  • burns

  • acute renal disease

  • musculoskeletal disease

  • trauma 

• less specific marker of liver inflammation compared to ALT

Describe alkaline phosphotase (ALP). Where is it found and what does it catalyse? Significantly elevated levels indicate:

• membrane bound enzyme present in all tissues and concentrated in liver, bile duct, kidney, bone, placenta

• substrate P ←→ substrate + Pi

• elevated in: 

  • bile duct obstruction

Describe gamma-glutamyl transferase (GGT). Where is it found and what does it catalyse? Significantly elevated levels indicate:

• membrane bound enzyme present in liver, kidney, bile duct, pancreas, gallbladder, spleen, heart, brain, seminal vesicles

• 5-L-glutamyl-peptide + AA ←→ peptide + 5-L-glutamyl-AA

• elevated in:

  • liver diseases

  • biliary system diseases

  • pancreatic diseases

How is creatinine synthesised?

• muscle contraction involves interconversion of creatine to creatine phosphate and interconversion of ATP and ADP

• 1-2% spontaneously converted to creatinine 

• quantity of creatinine related to muscle mass

What are the characteristics of urinary creatinine excretion?

• freely filtered at glomerulus

• not reabsorbed in tubules, but some proximal tubular secretion that increases w decreased kidney function

• serum creatinine inversely related to urinary creatinine and GFR

• depends on age and body size

Write the Creatinine assay equations

1. creatinine → creatine 

   1. creatininase

2. creatine + H2O → sarcosine + urea

   1. creatinase

3. sarcosine + H2O + O2 → formaldehyde + glycine + H2O2 (1 mol H2O2 per mole of creatine)

   1. sarcosine oxidase 

4. 2 H2O2 + 4-aminoantipyrine + sodium p hydroxybenzoate → quinoneimine dye + 4 H2O

   1. peroxidase

A520 of quinoneimine dye = directly proportional to H2O2

How is urea synthesised? How is it used to evaluate kidney function?

• formed by condensation of 2 NH3 molecules and 1 CO2 molecule

• highly water soluble, non toxic, neutral pH

• functional role = N excretion

Urea measurement is used in addition to creatinine estimate the kidney function

High serum urea levels suggest impaired kidney function owing to acute or chronic kidney disease

Describe the urease assay?

1. urea → ammonia + carbamic acid

   1. urease + H2O

2. carbamic → ammonia

   1. decomposition

read A630 values

Describe the alanine aminotransferase assay for assessing liver function

1. alanine + 2 oxoglutaric acid → pyruvate + glutamate

   1. ALT

2. pyruvate + NADH + H+ → lactate + NAD+

   1. lactate dehydrogenase 

the rate of decrease in absorbance at A340nm measure the rate of ALT activity

• 1U ALT enzymic activity = 1umol alanine/min/L serum