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Clinical Of Renal Disease And Electrolyte

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What is the Nephron?
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The functional unit of the kidney.
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How many Nephrons are in a Kidney?
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Approximately 10^6.
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The Nephron is made up of 2 main parts. What are these?
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The Glomerulus The Tubule.
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What are the 6 functions of the Kidney (Renal)?
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Regulates volume of fluid in the blood Electrolyte balance (Sodium, Potassium, Chloride, Calcium, Magnesium, Phosphate). Acid-Base Balance Excretion of waste products (Creatinine, Urea and Uric acid). Vitamin D metabolism (conversion of 25-OH Vit D to 1-25 OH Vit D (active molecule) resulting in calcium balance). Production of erythropoietin (Growth factor for red blood cell production in the bone marrow).
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What is the function of the Glomerulus?
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Filtration. Fluid is filtered into the Bowman’s capsule (filtrate).
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What is the composition of the filtrate?
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Similar to plasma: H2O Glucose Electrolytes: Na, K, PO4, Cl, Mg, Bicarb Amino acids Waste products Small proteins
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What is the function of the Tubules?
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Reabsorption and Secretion. The net result is dependent on the body’s needs.
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Most Na/Cl, bicarb and glucose, Amino acids, phosphate and small proteins are secreated from the kidneys. True or False?
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False! Most of the time these substances are reabsorbed by the Tubules.
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Waste products of the kidney are mostly secreted from the body. True or False?
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True.
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What is Na and K controlled by?
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Aldosterone
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What is H2O controlled by?
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ADH
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What Renal function Tests exist?
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Glomerular Fitration Rate (GFR) Measurement of waste products in serum.
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What does the GFR test measure?
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The volume of fluid filtered through all glomeruli per time unit.
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What is the normal measurement for a GFR test?
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60 – 120 ml/min.
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How is the GFR test measured?
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Clearance studies Estimated GFR (eGFR)
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What is meant by “Clearance of a molecule”?
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Amount “cleared” by the kidney per time unit.
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What is the “ideal molecule”?
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Molecule completely filtered in the glomerulus. Not reabsorbed in the Tubules. Not secreted back into the tubules.
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What is the equation for a Molecule’s Clearance?
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Molecule’s Clearance = [molecule in urine] x volume / [molecule in serum] x time
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Which 2 clearance molecules exist?
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Inulin clearance (fulfils all criteria, but labour intensive) Creatinine clearance (does not fulfil all criteria. Secreted back into tubules and overestimates GFR).
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What is the estimated glomerular filtration rate (eGFR)?
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Based on an equation validated against a gold-standard renal clearance test.
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Why is eGFR rapidly replacing Creatinine clearance as the test which measures glomerular filtration?
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Because, whilst creatinine clearance requires a urine sample (hence 24 hours), eGFR only need a blood test!
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Hence which is the most common measure of GFR?
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eGFR!
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What are the eGFR and Creatinine clearance Units?
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mL/min/1.73 m^2.
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What is Creatinine?
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The waste product of muscle breakdown.
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Is Creatinine a sensitive marker to renal function?
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No! Creatinine levels stay within the normal ranges, even when chronic renal diseases are already established!
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What is Urea? (Hint: Think back to Biochemistry Metabolism in 1st Year)
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The waste product of protein and amino acid metabolism.
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Is Urea a good or poor indicator of renal function?
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Poor indicator. No longer used in some hospitals.
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What is serum Na+ an indicator of?
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Indicator of both H2O and Na status.
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Serum Na+ is under the control of which 2 hormones?
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Renin-angiotensin-aldosterone axis Antidiuretic hormone.
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Does serum K+ go up or down in renal failure and why?
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Goes up as Kidney is major route of K excretion and balance.
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What other factors can influence K+ concentration?
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Artefacts Drugs.
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In renal failure, what happens to the acid-base balance?
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There is metabolic acidosis (decreased acid excretion). Makes pH lower (increase in [H+]) and decrease in Bicarbonate excretion.
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What happens to the serum Ca2+ in renal failure diseases?
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Affected as Kidney involved in active Vitamin D production. Levels are usually low in both acute and chronic renal failure.
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What is the active form of Vitamin D?
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1-25 (OH)2 Vitamin D.
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What happens to the urinary protein during renal failure?
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Glomeruli damage causes protein to leak into tubules. The tubules cannot reabsorb enough protein back into the bloodstream. As a result (Nephrotic Syndrome) proteinuria is present.
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Which of the following are waste products? A) Sodium B) Potassium C) Creatinine D) Calcium
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C) Creatinine
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Which of the following analytes are handled by the renal tubules? A) Vitamin D B) Sodium C) Phosphate D) Potassium
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B) Sodium C) Phosphate D) Potassium
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If renal function is impaired, what do you expect to happen to the following functions (increase or decrease)? Glomerular Filtration Rate Waste product blood concentration Active Vitamin D Synthesis Urine protein
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Glomerular Filtration Rate DECREASES Waste product blood concentration INCREASES Active Vitamin D Synthesis DECREASES Urine protein INCREASES
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What are the causes of Acute renal failure?
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Acute onset of decreased renal function (hours/days) caused by: Hypovolaemia secondary to blood loss, dehydration and shock. Acute inflammatory process affecting glomeruli (glomerulonephritis) Drugs affecting glomeruli or tubules Massive muscle breakdown (rhabdomyolysis) Obstruction of renal flow.
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What are the Biochemical changes in Acute renal failure?
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Decreased GFR – rapid decrease in urine volume (may show anuria). Accumulation of waste products in blood: Increased serum Urea and serum Creatinine. Accumulation of electrolytes for which the main route of excretion is the kidney: Increased serum K+ and PO4-. Accumulation of acids due to decreased H+ excretion Serum Na+ usually decreased due to H2O retention.
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Myoglobin is toxic to renal tubular cells. True or False?
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True.
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What are the causes of chronic renal failure?
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Gradual decline of renal function, over years is caused by: Diabetes (diabetic nephropathy) Hypertension Diseases affecting glomeruli, tubules or renal interstitium.
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What are the Biochemical changes in chronic kidney disease?
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CKD classified into stages according to eGFR. Changes are similar to those of ARF but occur slowly. Accumulation of waste products in blood: Increased serum Urea and serum Creatinine. Accumulation of electrolytes for which the main route of excretion is the kidney: Increased serum K+ and PO4- Accumulation of acids due to decreased H+ excretion. Impairment of other renal functions: Decreased serum Ca2+ due to decreased active Vitamin D production.
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A patients renal function is considered abnormal when the eGFR reading is below how much ml/min?
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Lower than 60 ml/min.
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H2O and Na+ balances are coupled. True or False?
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True.
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What does the hormone released from the adrenals: renin/angiotensin/aldosterone axis affect?
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Na+, H20 and K+
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What does the hormone released from the posterior pituitary: antidiuretic hormone (ADH), also called arginine-vasopressin (AVP) affect?
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H2O only!
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What is Hyponatraemia?
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The loss of Na+ and/or excess of H2O. Serum Na+ < 135 mmol/L.
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What can Hyponatraemia cause?
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Central nervous system symptoms due to shifts of H2O between extracellular fluid and cells.
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What is Hypernatraemia?
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Usually loss of H2O. Rarely excess Na+! Serum Na+ > 145 mmol/L.
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What can Hypernatraemia cause?
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Central nervous system symptoms due to shifts of H2O between cells and extracellular fluid.
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What is Dehydration? Hypo- or Hypernatraemia?
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Loose term indicating loss of body water. If loss of fluid (sweat, diarrhoea, vomiting) and poor fluid replacement, may develop hypernatraemia: Increased serum [Na+]. If loss of fluid and replacement of water only, may develop hyponatraemia: Decreased serum [Na+].
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The Kidney usually preserves Na+ at the expense of K+. True or False?
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True.
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What is acidosis usually associated with?
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Increased serum K+. Alkalosis usually associated with decreased serum K+.
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What is Hyperkalaemia and what causes it?
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Serum K+ > 5.5 mmol/L. Caused by: Artefacts: haemolysis, cold weather, delayed sample processing, high platelets. Increased intake Increased renal reabsorption Decreased loss e.g. CRF and ARF.
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What does Hyperkalaemia cause?
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Changes to the heart rhythm (arrhythmia).
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What is Hypokalaemia and what causes it?
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Serum K+ < 3.5 mmol/L. Caused by: Artefacts: hot weather Decreased intake Decreased renal reabsorption Increased loss: vomiting/diarrhoea/kidneys.
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What can Hypokalaemia cause?
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Changes to heart rhythm (arrhythmia) Muscle weakness.
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Dehydration is equal to hypernatraemia. True or False?
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False. Dehydration is both Hyper- and Hyponatraemia.
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Potassium may be low if the sample is haemolysed. True or False?
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False. Potassium is high!
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Abnormalities of Potassium can affect heart rhythm. True or false?
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True.
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Hyponatraemia can be due to excessive water-with-little-salt-content (hypotonic fluid) replacement. True or False?
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True.