WBR0547
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| Author | [[PageAuthor::Serge Korjian M.D. (Reviewed by Serge Korjian)]] |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Physiology |
| Sub Category | SubCategory::Renal |
| Prompt | [[Prompt::Mr. Jones is a 48-year-old man with history of chronic kidney disease who presents to the nephrology clinic for follow-up. He tells you that he was recently admitted to the hospital for shortness of breath and was diagnosed with heart failure. You explain to him that with his heart failure, blood flow to the kidneys is likely to decrease causing him to retain salt and water. Which of the following curves best represents the behavior of the substance that can be used to measure this patient's renal blood flow?
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| Answer A | AnswerA::A |
| Answer A Explanation | AnswerAExp::This curve represents the concentration of PAH along the proximal convoluted tubule. Notice the sharp increase compared to curve B which represents creatinine concentration. This is due to the active secretion of PAH. |
| Answer B | AnswerB::B |
| Answer B Explanation | AnswerBExp::This curve represents the concentration of creatinine along the proximal convoluted tubule. It closely follows to the glomerular filtration rate. |
| Answer C | AnswerC::C |
| Answer C Explanation | AnswerCExp::This curve shows the concentration of chloride. Initially reabsorption is of chloride is slowed by bicarbonate reabsorption. After 25% of the length has passed, chloride reabsorption follows sodium reabsorption (Blue Curve). |
| Answer D | AnswerD::D |
| Answer D Explanation | AnswerDExp::Curve D shows potassium concentration along the proximal tubule. |
| Answer E | AnswerE::E |
| Answer E Explanation | AnswerEExp::Curve E shows bicabonate concentration along the proximal tubule. |
| Right Answer | RightAnswer::A |
| Explanation | [[Explanation::Para-aminohippurate (PAH) is a derivative of hippuric acid that is filtered by the glomeruli and actively secreted by the proximal tubules. At low plasma concentrations, >90% of PAH is cleared from the blood by the kidneys in a single circulation. It is used to measure effective renal plasma flow (ERPF) since it has a high clearance, and is nontoxic at recommended doses. Curve A shows the effective concentration of PAH along the length of the proximal tubule. Notice how it increases more rapidly than creatinine concentration given that creatinine is filtered but only slightly secreted compared to PAH that is significantly secreted by the proximal tubule.
ERPF is analogous to the clearance of PAH and is calculated using the following equation:
U = urinary PAH concentration, V = Urinary flow rate, P = Plama PAH concentration Renal blood flow (RBF) can be calculated using the patient's hematocrit and the ERPF as follows:
RBF = ERPF/(1-Hct) |
| Approved | Approved::No |
| Keyword | WBRKeyword::Para-aminohippurate, WBRKeyword::PAH, WBRKeyword::Effective renal plasma flow, WBRKeyword::ERPF, WBRKeyword::RBF, WBRKeyword::Proximal tubule, WBRKeyword::Renal physiology |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |
