USMLE Step 1 Renal Physiology 1 Review 58 12 Glomerular Filtration

USMLE Step 1 Renal Physiology 1 Review 58 12 Glomerular Filtration

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Play USMLE Audio MP3 58 12 Glomerular Filtration Below

Begin 58 12 Glomerular Filtration Transcription

Moving now to nephron function. The nephron’s function: to clear the plasma of unwanted substances which are then excreted in the urine and to reabsorb substances needed by the body and return them to the blood.

What is the first step in this process? It starts with GF.

  • Glomerular filtration.

When we talk about glomerular filtration we’re talking about fluid passing from where to where?

  • From the glomerular capillaries into Bowman’s capsule.

What is the term for the total volume of plasma filtered each minute by all the glomeruli in both kidneys?

  • The total volume of plasma filtered each minute by all the glomeruli is the glomerular filtration rate, the GFR.

What is the equation called that can be used to calculate the glomerular filtration rate? It starts with SE.

  • The Starling equation. Before we get in to how to use the Starling equation, let’s just discuss a few of the things involved here.

First, pressure differences between what two parts of the nephron are part of the Starling equation? They start with GC and BS.

  • The glomerular capillaries and Bowman’s space.

And what is Bowman’s space?

  • The space between the glomerular capillaries and Bowman’s capsule is called Bowman’s space.

What are the two pressure gradients that affect glomerular filtration? They start with H and O.

  • Hydrostatic and oncotic.

What is oncotic pressure? The answer starts with COP.

  • Colloid osmotic pressure.

Which one of these pressure gradients promotes filtration?

  • The hydrostatic pressure gradient promotes filtration.

What opposes filtration?

  • The oncotic or colloid osmotic pressure in the glomerular capillaries.

So, when does filtration occur?

  • Filtration occurs when hydrostatic pressure gradient exceeds the oncotic pressure in the glomerular capillaries.

Student doctor, please pause the tape and summarize what we’ve discussed about the glomerular filtration rate and the things involved in calculating it.

The nephron’s function to clear the plasma of unwanted substances which are then excreted in the urine and to reabsorb substances needed by the body and return them to the blood. Glomerular filtration is the first step in this process. When we talk about glomerular filtration we’re talking about fluid passing from the glomerular capillaries into Bowman’s capsule. The total volume of plasma filtered each minute by all the glomeruli in both kidneys is the glomerular filtration rate which can be calculated using the Starling equation. Two pressure gradients between the glomerular capillaries and Bowman’s space are part of this calculation. Bowman’s space is the space between the glomerular capillaries and Bowman’s capsule. The hydrostatic pressure gradient which promotes filtration and the oncotic pressure gradient which opposes filtration both affect glomerular filtration. Oncotic pressure is the colloid osmotic pressure. When the hydrostatic pressure gradient exceeds the oncotic pressure in the glomerular capillaries filtration occurs.

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