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Questions and Answers
What is the primary cause of urinary concentrations of substances?
What is the primary cause of urinary concentrations of substances?
- Glomerular function
- Tubular function (correct)
- Plasma ultrafiltrate
- Renal blood flow
What is a characteristic of proximal tubular failure?
What is a characteristic of proximal tubular failure?
- High pH level
- Increased sodium concentration
- Low bicarbonate concentration and low pH (correct)
- High bicarbonate concentration
What is a consequence of distal tubular failure?
What is a consequence of distal tubular failure?
- Increased phosphorus excretion
- Decreased urine volume
- Increased urine volume, even with low renal blood flow (correct)
- Increased glucose reabsorption
What is a characteristic of proximal and/or distal tubular failure?
What is a characteristic of proximal and/or distal tubular failure?
What is a characteristic of proximal tubular failure?
What is a characteristic of proximal tubular failure?
What is the name of the process by which the tubules reabsorb water?
What is the name of the process by which the tubules reabsorb water?
What is the effect of a small impairment of reabsorption on urine volume?
What is the effect of a small impairment of reabsorption on urine volume?
What is the approximate percentage of filtered water that is normally reabsorbed by the tubules?
What is the approximate percentage of filtered water that is normally reabsorbed by the tubules?
What is the primary cause of oliguria in acute kidney injury?
What is the primary cause of oliguria in acute kidney injury?
What is the primary goal when examining a patient with acute kidney injury?
What is the primary goal when examining a patient with acute kidney injury?
What is a common symptom of acute kidney injury?
What is a common symptom of acute kidney injury?
What is the purpose of renal tract imaging in acute kidney injury?
What is the purpose of renal tract imaging in acute kidney injury?
What is an example of a pre-renal cause of acute kidney injury?
What is an example of a pre-renal cause of acute kidney injury?
What is a complication of acute kidney injury?
What is a complication of acute kidney injury?
What percentage of filtered water is reabsorbed from the tubular lumen?
What percentage of filtered water is reabsorbed from the tubular lumen?
Which of the following waste products is not reabsorbed from the tubular lumen to a significant degree?
Which of the following waste products is not reabsorbed from the tubular lumen to a significant degree?
What is the primary function of the tubular cells in the proximal tubules?
What is the primary function of the tubular cells in the proximal tubules?
What is the approximate volume of water that enters the loops of Henle daily?
What is the approximate volume of water that enters the loops of Henle daily?
What happens to most of the filtered urea?
What happens to most of the filtered urea?
What is the approximate volume of water that is reabsorbed from the proximal tubules?
What is the approximate volume of water that is reabsorbed from the proximal tubules?
What is the primary function of the loops of Henle?
What is the primary function of the loops of Henle?
What ions are actively reabsorbed from the proximal tubules?
What ions are actively reabsorbed from the proximal tubules?
What is the function of the impermeable layer?
What is the function of the impermeable layer?
Which part of the kidney has a higher concentration of solutes?
Which part of the kidney has a higher concentration of solutes?
What is the direction of water flow in the cortex?
What is the direction of water flow in the cortex?
What is the role of the renal counter-regulatory system?
What is the role of the renal counter-regulatory system?
What is the difference in solute concentration between the cortex and medulla?
What is the difference in solute concentration between the cortex and medulla?
What is the purpose of the cortex in the renal counter-regulatory system?
What is the purpose of the cortex in the renal counter-regulatory system?
What happens to the solute concentration as you move from the cortex to the medulla?
What happens to the solute concentration as you move from the cortex to the medulla?
What is the role of the medulla in the renal counter-regulatory system?
What is the role of the medulla in the renal counter-regulatory system?
What is the effect of a high water intake on the extracellular fluid?
What is the effect of a high water intake on the extracellular fluid?
Why are osmotic diuretics infused and not absorbed from the gut?
Why are osmotic diuretics infused and not absorbed from the gut?
What is the effect of maximal water diuresis on the osmolality at the tips of the medullary loops?
What is the effect of maximal water diuresis on the osmolality at the tips of the medullary loops?
What is the main effect of sodium reabsorption in exchange for hydrogen ions in the proximal tubules?
What is the main effect of sodium reabsorption in exchange for hydrogen ions in the proximal tubules?
What is the effect of aldosterone on the nephron?
What is the effect of aldosterone on the nephron?
What is the result of increasing the circulating volume?
What is the result of increasing the circulating volume?
What is the effect of rapid flow in the vasa recta on the medullary hyperosmolality?
What is the effect of rapid flow in the vasa recta on the medullary hyperosmolality?
What is the exchange process in the distal tubules and collecting ducts associated with?
What is the exchange process in the distal tubules and collecting ducts associated with?
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Study Notes
Nephron Function
- Nephrons reabsorb 99% of filtered water, amounting to 140-160 L/day.
- 70-80% of filtered water is reabsorbed in the proximal tubules.
- Tubular cells do not actively deal with waste products like urea and creatinine.
- Most filtered urea is excreted in urine, contributing to its osmolality.
Solute Reabsorption
- Almost all potassium is actively reabsorbed from the proximal tubules.
- Over 70% of filtered sodium, free ionized calcium, and magnesium are reabsorbed from the proximal tubules.
Renal Counter-Regulatory System
- A high water intake dilutes the extracellular fluid, reducing ADH secretion.
- The collecting ducts remain impermeable to water, producing a dilute urine and a high osmolality within the medulla and medullary vessels.
- The countercurrent multiplication process helps correct the fall in systemic osmolality.
Osmotic Diuretics
- Effective osmotic diuretics cannot cross cell membranes to a significant degree.
- Mannitol, a sugar alcohol, is an example of an osmotic diuretic used therapeutically.
Homeostatic Solute Adjustment
- Sodium reabsorption in exchange for hydrogen ions occurs throughout the nephrons.
- In the proximal tubules, this exchange helps reabsorb filtered bicarbonate.
- In the distal tubules and collecting ducts, the exchange process is associated with net generation of bicarbonate.
Clinical Manifestations of Tubular Failure
- Proximal tubular failure: low bicarbonate concentration, low pH, hypokalaemia, hypophosphataemia, hypomagnesaemia, and hypouricaemia.
- Distal tubular failure: pH inappropriately high compared to that in plasma.
- Proximal and/or distal tubular failure: increased volume, pH inappropriately high, generalized amino aciduria, phosphaturia, and glycosuria.
Acute Kidney Injury (AKI)
- Causes of AKI include pre-renal, renal, and post-renal factors.
- Pre-renal factors include hypovolaemia and hypotension.
- Renal factors include tubular damage and glomerular damage.
- Post-renal factors include urinary tract obstruction.
- Clinical history and examination are essential in diagnosing AKI and excluding reversible causes of pre-renal failure.
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