Renal Basics

Question 1

What is the most important function of the kidneys?

Answer 1

homeostasis with water and solute balance!

Question 2

What are some waste products the renal system removes?

Answer 2

creatinine
NH4
urea

Question 3

What are three ways the kidneys act as endocrine organs/

Answer 3

erythropoietin secretion
activates Vitamin D
renin secretion

Question 4

What are the three layers through which solutes need to travel to reach the filtrate in Bowman’s Space?

Answer 4

1. fenestrated capillary endothelium
2. glomerular basement membrane
3. podocytes with filtration slits

Question 5

What is the glomerular filtration rate?

Answer 5

It’s the combined rate of fluid movement from the glomerular capillary lumen to Bowman’s space for all the nephrons in both kidneys

Question 6

Only a small amount of albumin is filtered. What percentage is reabsorbed back into the blood? What happens if this doesn’t happen?

Answer 6

90% is reabsorbed back into the blood

A normal albumin excretion rate is about 10 mg per day. so a persistent AER over 30 mg is microalbuminuria and indicates early glomerular disease. Nephrotic syndromes can have AERs over 3,000!

Leads to a low albumin concentration in the plasma and thus a decreased oncotic pressure in the capillaries

Question 7

What is the glomerular filtration rate in liters per day?

Answer 7

180 L/day! (or 125 ml/min)

Question 8

What is the renal plasma flow?

Answer 8

So both kidneys combined get about 1000 ml/min of blood. hematocrit is 40%, so both kidneys combined receive 600 ml.min of plasma. This is the renal plasma flow

Question 9

What is the filtration fraction?

Answer 9

it’s the GPR divided by the renal plasma flow - so how much of the renal plasma flow gets filtered into bowman’s space. Actually 20%!

Question 10

What do NE and angiotenin II do to the afferent and efferent arterioles?

Answer 10

NE can constrict both the afferent arteriol and the efferent arteriole (but not necessarily at the same time)

Ang II can vasoconstrict the efferent arteriole only - good way to maintain a modicum of renal function even when sympathetics are in hyperdrive

Question 11

In adults, the GFR ____ with age and ____ with weight.

Answer 11

decreases with age and increases with weight

Question 12

What happens to pressure in the glomerular capillary when there is vasoconstriciton of the afferent arteriole?

Answer 12

it goes down because less blood is going into the GC

Question 13

What happens to the renal plasma flow when the afferent arteriole is vasoconstricted?

Answer 13

it goes down because less blood can go through

Question 14

What happens to the GFR when the afferent arteriole is constricted?

Answer 14

it goes down because there’s low pressure, therefore the hydrostatic force pushing the fluid into bowman’s space is decreased

Question 15

What happens to the pressure in the glomerular capillary when the efferent arteriole is vasoconstricted?

Answer 15

it goes up - blood backs up and increases pressure

Question 16

What happens to the renal plasma flow with vasoconstriction of efferent arteriole?

Answer 16

It goes down - less blood is getting through the system because of the downstream constriction

Question 17

What happends to GFR when the efferent artiole is constricted?

Answer 17

Remember that the glomerular capillary pressure has more of an impact in determining GFR than RPF.

GFR increases because the increased hydrostatic pressure pushes fluids into Bowman’s space

Question 18

What happens to the pressure in the glomerular capillaries whne both the afferent and efferent arterioles are constricted?

Answer 18

no net change because the two cancel each other out

Question 19

What happens to RPF when both the afferent and efferent arterioles are constricted?

Answer 19

it goes waaay down - blood just isn’t getting thorugh

Question 20

Wha thappens to the GFR when both the afferent and efferent arterioles are constricted?

Answer 20

either stays the same or goes down. The pressure in the glomerular capillary is normally more important in determining GFR than RPF

Question 21

Why is creatinine so special?!

Answer 21

It’s the only naturally-made solute that is not reabsorbed, secreted, produced or destroyed in the nephron….thus the filtered load of creatinin is exactly equal to the excretion rate of creatinine

this makes it the perfect marker for kidney function

Question 22

What’s the equation with creatining to find the GFR?

Answer 22

GFR = Urine filtration rate x [creatining]urine divided by [creatining’plasma

Question 23

If plasma creatinine increases by a factor of 2, what has happened to the GFR?

Answer 23

It’s fallen by half

Question 24

What does the blood urea nitrogen tell us?

Answer 24

plasma urea can only leave the body via the kidneys, so a decrease in GFR will result in an increased BUN