Renal Lectures Flashcards
What contributes to high glomerular filtration rates in healthy kidneys?
1) High blood hydrostatic pressures in the glomerular capillaries
2) High hydrostatic pressure of fluid in Bowman’s space
3) High permeability of the proximal tubule
4) High rate of water reabsorption in the proximal tubule
5) Low circulating blood volume
(1) The hydrostatic blood pressure in renal glomerular capillaries is approximately 60mmHg. GFR generally remains constant even when the systemic blood pressure changes. Conditions which cause a large drop in the hydrostatic pressure within the glomerular capillaries such as low circulating blood volume from hypovolaemia, circulatory collapse or heart failure will result in a fall in GFR manifesting as Acute Kidney Injury (AKI).
Which option is CORRECT regarding the formation of urine?
1) Acidification of urine occurs at the loop of Henle
2) Aldosterone increases sodium reabsorption at the proximal tubule
3) Reabsorption of water and sodium is regulated by counter-current multiplication in the loop of Henle
4) The concentration of urine occurs only at the distal tubule.
5) There is almost complete reabsorption of glucose and amino acids in the loop of Henle
(3)
65% of filtered water and sodium is reabsorbed in the proximal tubule together with almost complete reabsorption of glucose (SGLT1 and 2) and amino acids. Counter-current multiplication is where an osmotic gradient is created in the medulla of the loop of Henle which allows passive resorption of water from the tubular fluid in response to the concentration gradient causing concentration of urine. Aldosterone increases sodium reabsorption in the distal tubule.
Acidification of urine occurs in the proximal and distal tubules.
Which hormone contributes to the development of renal bone disease in advanced stages of CKD?
(1). Aldosterone
(2) Antidiuretic hormone
(3). Atrial natriuretic peptide
(4). Calcitriol
(5). Renin and Angiotensin system
(4)
Calcitriol is a hormone secreted by the kidneys which promotes renal tubular reabsorption of calcium in the kidneys and stimulates the release of calcium stores from the skeletal system.
Aldosterone, ADH, ANP and the RAAS system contribute to the renal control of Effective Circulating Volume.
The RAAS system is stimulated by the juxtaglomerular apparatus in response to low circulating volumes. Ang-1 is converted to Ang-2 in the lungs in response to renin. Ang-2 increases both renal sodium reabsorption and aldosterone release.
Aldosterone is a mineralocorticoid hormone, secreted by the adrenal glands in response to Ang-2. Aldosterone increases sodium reabsorption in the distal tubule in exchange for hydrogen or potassium.
ANP is secreted from the atria in response to increased myocyte stretch caused by increased circulating volume. ANP promotes natriuresis by causing renal vasodilation increasing renal blood flow and hence GFR which in turn increases the excretion of sodium and hence water.
ADH is released in response to low circulating volume and essentially increases the permeability of the collecting ducts to water allowing more water to be drawn out by the vasa recta creating a more concentrated urine.
Which statement is correct regarding oliguria?
(1) Oliguria in AKI rarely responds to fluid challenges
(2) Oliguria is defined as urine output < 0.1ml/kg/hr
(3) Oliguria is defined as urine output < 0.2 ml/kg/hr
(4) Oliguria is defined as urine output < 0.5ml/kg/hr
(5) Oliguria is defined as urine output < 50ml/hr
(4)
Oliguria is defined as a urine output of <0.5ml/kg/hr and occurs in response to severe decreases in renal blood flow. Oliguria is a clinical characteristic of AKI and used in the severity grading of AKI stages 1-3.Treatment depends on the underlying cause, but oliguria frequently responds to fluid challenges and expansion of the circulating volume.
The transcellular shift of which cation is affected by acid-base imbalance?
(1) Calcium
(2) Chloride
(3) Phosphate
(4) Potassium
(5) Sodium
(4)
Metabolic acidosis is frequently associated with hyperkalaemia and alkalosis is associated with hypokalaemia due to transcellular shifts of potassium in exchange for hydrogen ions. Correction of acidosis or alkalosis is required to ensure that correction of abnormal potassium levels in the blood is maintained.
An increase in acid load can lead to rapid regulation of acid-base balance within seconds with various buffers in the body. Phosphate acts as a buffer predominantly in intracellular fluid. Other buffers include bicarbonate in extracellular fluid and carbonate in bones.
In which situation is it important to measure the anion gap?
(1) Differentiating between alkalosis and acidosis
(2) Metabolic acidosis
(3) Metabolic alkalosis
(4) Respiratory acidosis
(5) Respiratory alkalosis
(2)
T
he anion gap is used in evaluating metabolic acidosis to determine the presence and quantity of unmeasured anions. The anion gap is the difference between measured cations (sodium and potassium) and measured anions (chloride and bicarbonate) and can help differentiate between causes of metabolic acidosis.
Anion Gap = (Na+ + K+) – (Cl- + HCO3-)
Normal levels = 4 to 12 mEq/L
High anion gap acidosis is most often due to ketoacidosis, lactic acidosis, chronic kidney disease, or certain toxic ingestions.
Normal anion gap acidosis is most often due to gastrointestinal or renal HCO3− loss or renal failure to secrete H+ (Renal tubular acidosis (RTA) type 1 (distal RTA) and type 2 (proximal RTA).
Which of the following is a correct statement regarding acid-base homeostasis?
(1) Metabolic acidosis can occur because of failure of bicarbonate reabsorption in the distal tubule
(2) Metabolic acidosis can occur because of failure of hydrogen secretion in the proximal tubule
(3). Metabolic alkalosis can occur in type 4 renal tubular acidosis
(4). Metabolic acidosis is associated with increased aldosterone levels
(5). Metabolic acidosis associated with AKI is often associated with hyperkalaemia
(5)
Acidification of urine normally occurs in the proximal and distal tubules.
In the proximal tubule, 80-90% of filtered bicarbonate is reabsorbed back into the systemic circulation. The pH of urine falls from 7.4 to 6.7 from start to end of proximal tubule due to this process.
In the distal tubule and collecting ducts, hydrogen ions and ammonia are secreted in response to increased acid load by the intercalating cells. Renal tubular acidosis (RTA) is a clinical syndrome characterised by hyperchloraemic metabolic acidosis with a normal serum anion gap.
In Type 2 (proximal) RTA, tubular dysfunction cause failure to reabsorb bicarbonate together with other important electrolytes such as phosphate.
In Type 1 (distal RTA), tubular dysfunction causes failure to secrete hydrogen from the distal tubule.
Type 4 RTA results from low aldosterone levels or lack of effect of aldosterone on the distal tubule results in normal anion gap acidosis and hyperkalaemia.
Alkali and electrolyte correction in the mainstay of treatment in all forms of RTAs and fludrocortisone can be considered in cases of mineralocorticoid deficiency in Type 4 RTA.
Metabolic alkalosis is associated with increased aldosterone levels.
Which of these methods of assessing kidney function is most suitable for screening for chronic kidney disease (CKD) in the population?
1 - Estimated GFR and urine albumin: creatinine ratio (ACR)
2 - Iohexol creatinine clearance
3 - Renal ultrasound screening
4 - Serum creatinine levels
5 - Urine dipstick
(1)
Iohexol creatinine clearance is a gold standard measurement for accurate GFR levels however not appropriate for large population screening programmes. Serum creatinine levels are variable according to patient characteristics. Estimated GFR based on serum creatinine levels correcting for variables are reported with kidney function blood test in UK. Estimated GFR together with urine ACR are used for staging CKD.
Which option is a common complication of kidney disease?
1 - Hyperkalaemia
2 - Hypophosphataemia
3 - Metabolic Alkalosis
4 - Osteoporosis
5 - Polyuria
(1)
In addition to assessing kidney function, the presence of any complications of kidney disease needs to be determined with suitable investigations. Complications include metabolic acidosis, electrolyte disturbances including hyperkalaemic, uraemia and in the acute setting in some cases, oliguria. Acute and chronic kidney disease are associated with high phosphate levels. Chronic kidney disease is associated with metabolic renal bone disease as a result of hyperparathyroidism, hypocalcaemia, activated Vitamin D deficiency and hyperphosphataemia.
Which investigation is least often required to investigate AKI for the majority of patients presenting to hospital with AKI?
1 - Baseline and current creatinine and estimated GFR levels
2 - Blood pH and bicarbonate levels
3 - Serum antineutrophil cytoplasmic antibody (ANCA)
4 - Urea and electrolytes
5 - Urine dipstick
(3)
Assessment of AKI requires understanding of what complications can arise as a result of acute renal dysregulation. Regular monitoring of urea and electrolyte levels together with renal function is required even in the recovery phase as renal tubular function can take time to recover. A urine dipstick is helpful in determining potential causes of AKI and if blood and protein are present may indicate glomerular disease. Metabolic acidosis requires assessment of blood pH and serum bicarbonate levels. Serum ANCA levels may be indicated in rare circumstances of AKI when vasculitis/glomerulonephritis is suspected but should not be performed in all cases of AKI.
