USMLE Step 1 Renal Physiology 1 Review 58 16 Reabsorption & Secretion

USMLE Step 1 Renal Physiology 1 Review 58 16 Reabsorption & Secretion

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Play USMLE Audio MP3 58 16 Reabsorption & Secretion Below

Begin 58 16 Reabsorption & Secretion Transcription

Let’s move on to how the renal tubules work. After filtration occurs, where does the unfiltered blood go? The answer starts with PC.

  • After filtration the unfiltered blood flows into the peritubular capillaries.

What are we including here when we talk about the peritubular capillaries?

  • The vasa recta.

What structures carry the unfiltered blood into the peritubular capillaries and the vasa recta?

  • The efferent arterioles.

Where does the glomerular filtrate go first? The answer starts with BC.

  • The glomerular filtrate first goes into Bowman’s capsule.

What is the term for the amount of a given solute that crosses the filtration barrier and enters the renal tubule per unit time? It starts with FL.

  • The filtered load.

What is the equation for the filtered load?

  • The filtered load equals the glomerular filtration rate times the concentration of the substance in the plasma.

What two processes involve the movement or transfer of solutes between the tubule lumen and the peritubular capillaries?

  • Renal tubular reabsorption and renal tubular secretion.

Which one is the transfer of substances from the peritubular capillaries into the tubule lumen?

  • Secretion is the transfer or movement of solutes from the peritubular capillaries into the tubule lumen.

And what is happening to the glomerular filtrate with secretion?

  • With secretion, substances are being added to the glomerular filtrate.

What happens to the filtrate with reabsorption?

  • With reabsorption, substances are being removed from the glomerular filtrate.

So what is reabsorption?

  • Reabsorption is the movement of solutes and water from the tubule lumen into the peritubular capillaries.

What is the only organic substance that is both reabsorbed and secreted by the kidneys? It starts with UA.

  • Uric acid.

In terms of filtered load and excreted amount, how is the reabsorbed amount of a substance calculated?

  • The amount of a substance that is reabsorbed equals the filtered load minus the excreted amount.

How is the amount secreted calculated?

  • Amount secreted equals the excreted amount minus the filtered load.

Student doctor, please pause the tape and summarize what we’ve discussed about what happens to the unfiltered blood and the glomerular filtrate after filtration occurs as well as renal tubular reabsorption and secretion.

After filtration occurs, the unfiltered blood enters the peritubular capillaries, including the vasa recta, via the efferent arteriole. The glomerular filtrate first goes into Bowman’s capsule. The amount of a solute that crosses the filtration barrier and enters the renal tubule per unit time is called the filtered load. The equation for this is filtered load equals the GFR times the concentration of the substance in plasma. Renal tubular secretion is when solutes transfer from the peritubular capillaries into the tubule lumen. In other words, when a substance is added to the glomerular filtrate. Renal tubular reabsorption is when water and solutes move from the tubule lumen into the peritubular capillaries. With reabsorption, a substance is removed from the glomerular filtrate. The only organic substance that is both reabsorbed and secreted by the kidneys is uric acid. The amount of a substance that is reabsorbed is equal to the filtered load minus the excreted amount. And the amount secreted equals the excreted amount minus the filtered load.

****END OF TRANSCRIPTION****

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