Multiple Choice
Which of the following forces opposes glomerular filtration?
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25. The Urinary System
Renal Physiology: Regulation of Glomerular Filtration
Problem L3.A2
Textbook Question
Mr. Yao is a patient with kidney disease who presents to your clinic for monitoring. You notice on his chart that his GFR was estimated through inulin administration to be about 35 ml/min. What does this tell you about the health of his kidneys? Mr. Yao is taking a medication that is normally excreted from the body in the urine. You order blood work and find that the concentration of this medication in his plasma is much higher than normal. How does his decreased GFR explain the elevated level of medication in his plasma?
Verified step by step guidance1
Step 1: Understand the concept of Glomerular Filtration Rate (GFR). GFR is a measure of how well the kidneys filter blood. A normal GFR is typically around 90-120 ml/min. A GFR of 35 ml/min indicates significantly reduced kidney function, which is consistent with kidney disease.
Step 2: Recognize the role of the kidneys in excreting medications. The kidneys filter waste products and medications from the blood into the urine. If kidney function is impaired, the filtration process is less efficient, leading to reduced excretion of medications.
Step 3: Relate decreased GFR to medication clearance. With a GFR of 35 ml/min, Mr. Yao's kidneys are filtering blood at a much slower rate. This means that the medication is not being removed from the plasma as effectively, causing its concentration in the blood to rise.
Step 4: Consider the implications of reduced medication excretion. The elevated plasma concentration of the medication could lead to toxicity or reduced therapeutic effectiveness. Adjustments to the medication dosage may be necessary to account for impaired kidney function.
Step 5: Highlight the importance of monitoring kidney function and medication levels. Regular blood work and GFR assessments are crucial for patients with kidney disease to ensure proper medication management and prevent complications.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Glomerular Filtration Rate (GFR)
GFR is a measure of how well the kidneys filter blood, specifically the volume of fluid filtered from the renal glomeruli into the Bowman's capsule per minute. A normal GFR is typically around 90-120 ml/min, and a GFR of 35 ml/min indicates significantly reduced kidney function, suggesting chronic kidney disease or acute kidney injury. This reduction in GFR can lead to the accumulation of waste products and medications in the bloodstream.
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Glomerular Filtration Rate
Renal Excretion of Medications
Many medications are eliminated from the body through renal excretion, which involves filtration, secretion, and reabsorption processes in the kidneys. When GFR is decreased, the kidneys are less effective at filtering these medications from the blood, leading to higher plasma concentrations. This can result in potential toxicity or adverse effects, as the body is unable to clear the drug efficiently.
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Pharmacokinetics in Kidney Disease
Pharmacokinetics refers to how the body absorbs, distributes, metabolizes, and excretes drugs. In patients with kidney disease, altered pharmacokinetics can affect drug dosing and efficacy. With a decreased GFR, the clearance of renally-excreted medications is impaired, necessitating careful monitoring and potential dosage adjustments to avoid toxicity and ensure therapeutic effectiveness.
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