Most Things Biology

Urinary Lab Part 2: Filtration

Part 2 of the urinary lab. Three pressures act on one capillary bed; what is left over is what gets filtered.

1 · The pressure sandbox

NFP = GHP − (BCOP + CsHP)   ·   GFR = Kf × NFP

Blood pressure arriving through the afferent arteriole. Pushes fluid out.
Pull from plasma proteins that stay in the blood. Holds fluid in.
Back-pressure from filtrate already in the capsular space, backing up from the PCT. Pushes back.
Surface area × how leaky the barrier is. Not a pressure.
The three filtration pressures on a renal corpuscle A renal corpuscle in section: the afferent arteriole enters at upper left, the pink glomerular capillaries fill the middle, the brown capsular space surrounds them and drains to the right into the proximal convoluted tubule. Three labelled arrows sit on it. GHP starts in the afferent arteriole and points into the glomerulus. BCOP starts in the pink capillary blood and points back toward the arterioles. CsHP starts in the proximal convoluted tubule and points back into the capsular space. Each arrow gets longer and heavier as its pressure rises. A fourth arrow at lower right shows the net filtration pressure: green and pointing toward the tubule when filtration happens, red and pointing back when it does not. afferent arteriole efferent arteriole PCT capsular space
Each arrow starts where its pressure comes from, and gets longer and heavier as the pressure rises. The arrow at lower right is what is left over.
NFP10 mmHg
GFR125 mL/min
Per day180 L

2 · Five scenarios — predict, then apply

Choose what you think each pressure does before you press the button. One card per person.

3 · Autoregulation

Mean arterial pressure now drives GHP. Record a reading at each pressure with the mechanism off, then switch it on and do the sweep again.

GHP55 mmHg
GFR125 mL/min

Recorded autoregulation readings
MAPAutoregulationGHPGFR
GFR against mean arterial pressure Your recorded points. Squares are readings with autoregulation off; circles are readings with it on.
Points appear as you record them. Rebuild this graph on your Miro board.