Flashcards in Renal Filtration and Blood Flow Deck (51)
What are the 3 general processes that determine the amount of a substance that appears in urine?
1) Glomerular filtration
2) Reabsorption of the substance from tubular fluid back into blood
3) Secretion of the substance from blood into tubule fluid.
What is the first step in the production of urine?
Ultrafiltration of the plasma by the glomerulus
How much of the cardiac output do the kidneys receive and why?
They receive 25% of the CO which far exceeds their metabolic need and this allow for flow to be adjusted with demand as in when working out.
What is the filtration fraction?
Ratio of GFR/RPF
What is the normal value of the filtration fraction?
What is the composition of the ultra filtrate like?
The ultrafiltrate is devoid of cellular elements and is essentially protein free. The salt and organic compound concentrations are similar in the ultrafiltrate and
How are GFR and RFP regulated?
What is the filtration barrier in the renal corpuscle based upon?
Size and Charge
What size particles are freely filtered?
Particles less than 7000 Da and 20 Å are freely filtered
What size molecules are impermeable?
Molecules around 70000 Da and 42 Å are impermeable.
(Albumin is 66K Da and it is nearly impermeable)
What charge molecules are filtered more readily?
Cationic molecules are filtered more easily than anions
Why are proteins not filtered very easily, or at all?
Most proteins are negatively charged
Why are anions harder to filter?
The filtration barrier contains fixed polyanions that will repel the negatively charged proteins
How does glomerular capillary hydrostatic pressure affect filtration?
How does glomerular capillary oncotic pressure affect filtration?
How does Bowman space hydrostatic pressure affect filtration?
How does Bowman space oncotic pressure affect filtration?
What happens with higher GFR values?
It results in greater filtration and also greater water and salt excretion
What is the Bowman space oncotic pressure normally at?
0 as there is little protein in the BS to extrude water from the glomerulus
What is the equation for the net filtration pressure (NFP)?
NFP = (pGC - πGC) - (pBC - πBC)
What is the equation for the GFR?
GFR = kF(pGC - πGC - pBC)
kF = filtration coefficient
What happens to the πGC along the nephron?
The πGC increases along the nephron towards the end as the water leaves the tubule and the solutes concentrate in it.
What is kF?
It is the product of the intrinsic permeability of the glomerular capillary and the glomerular surface area available for filtration.
How is the GFR regulated normally?
It is regulated by changing the pGC
What are the ways that the pGC can be altered?
1. Changes in the afferent arteriolar resistance
2. Changes in the efferent arteriolar resistance
3. Changes in renal arteriolar pressure
How does an increase in the afferent arteriolar resistance affect the pGC?
Decreases the pGC
How does an increase in the efferent arteriolar resistance affect the pGC?
Increases the pGC
How does an increase in the blood pressure affect the pGC?
Increases the pGC
What are the changes that occur in kidney stones?
Increase the pBS which leads to decreased GFR