PhysiologyLesson 5 of 8 in the course The Urinary System

Glomerular Filtration, GFR Regulation, and Clearance

5 flashcards · 5 quiz questions · 5 match pairs · 5 fill-in sentences · English

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Summary

This lesson explains how the kidneys begin urine formation by filtering plasma at the glomeruli. It introduces glomerular filtration rate (GFR), the filtration barrier, and the pressures that determine the direction and amount of filtration.

Urine formation involves processes carried out at different parts of the nephron. Filtration moves water and small solutes from glomerular blood into Bowman’s capsule. Reabsorption returns useful substances and water from the tubular fluid to the blood, while secretion moves selected substances from blood into the tubule. Together, these processes modify plasma and produce urine.

All flashcards

Glomerular filtration rate (GFR)
The volume of filtrate formed by both kidneys per minute.
Net filtration pressure (NFP)
The pressure favoring filtration after opposing pressures are accounted for.
Inulin clearance
A close measure of GFR because inulin is filtered but neither reabsorbed nor secreted.
Creatinine clearance
A practical estimate of GFR; creatinine is not reabsorbed and is slightly secreted.
Renal autoregulation
Adjustment of renal blood flow that helps stabilize glomerular filtration across blood pressure changes.

Quiz questions

  1. When increased blood pressure stretches smooth muscle in the afferent vessels, what response helps limit the rise in filtration?Answer: The smooth muscle contracts, restricting blood flow into the glomerulus.
  2. Why does inulin clearance closely reflect GFR?Answer: Inulin is filtered and is neither reabsorbed nor secreted.
  3. What makes creatinine clearance an imperfect measure of GFR?Answer: A small amount of creatinine is secreted by the nephron.
  4. Why can GFR estimates help clinicians choose doses of some medications?Answer: Reduced renal excretion can cause these medications to accumulate.
  5. Below approximately what mean arterial pressure may glomerular filtration become impaired?Answer: 60 mm Hg

Based on Anatomy and Physiology 2e by J. Gordon Betts, Kelly A. Young, James A. Wise, Eddie Johnson, Brandon Poe, Dean H. Kruse, Oksana Korol, Jody E. Johnson, Mark Womble, Peter DeSaix (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.

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