RENAL 02: CLEARANCE

Question 1

What is the definition of load and what are the units for it?

Answer 1

The product of its concentration * the flow

mg/min

Question 2

How many input and output loads does the kidney have? What is the relationship between these?

Answer 2

One input (arterial plasma load)

Three outputs (venous, ureter, lymph)

Total input load must equal output loads

Arterial plasma load of substance x = the ureter, venous, and lymphatic loads of that same substance X, summed

We typically ignore lymphatic load because it is so small, and we typically ignore venous load since it turns into the arterial load next cycle

Question 3

How do you calculate load

Answer 3

Load (mg/min) = concentration (mg/mL) * flow (mL/min)

Therefore, the mL cancel out

Question 4

Renal clearance

Answer 4

The volume of plasma cleared of any substance in one minute (therefore mL/min)

Question 5

How do we calculate renal clearnace

Answer 5

Clearance of substance X is equal to the ureter concentration times flow of that substance, over the plasma concentration of it, where X is netiher produced nor consumed by the kidneys

Question 6

If something is completely cleared once filtered (cannot be secreted nor reabsorbed), then what can we say about its clearance?

Answer 6

It will equal the renal blood flow

Question 7

Can clearance exceed 660?

Answer 7

NO

Clearance cannot expand into hematocrit, it can only eat into maximum renal plasma flow

Question 8

What is another way we can think of the loads on the kidney? Think of 4 major loads overall associated with an equation we talked about eralier

Answer 8

Filtered load

Secreted load

Reabsorbed load

excreted load

this still gets back into input load = output load

F+S=R+E

Question 9

Glomerular filtration rate i what?

Answer 9

The volume of filtrate per unit time in the kidney; it is the rate of volume going through the glomerulus at any point in time (therefore it is NOT the renal plasma flow).

A normal GFR is about 120-125, and down to 15 is renal failure

Question 10

How do you determine GFR?

Answer 10

You must use something of known concentration and WILL b cleared if present

Question 11

Substances we can use to measure GFR

Answer 11

Creatinine

Inulin

Question 12

How is inulin used to measure GFR? What is it?

Answer 12

It is a complicated plant oligosaccharide which will be filtered and excreted but not reabsorbed or secreted, nor can we modify it. Therefore, F=E

Question 13

What is creatinine?

Answer 13

It is an end-product of muscle metabolism; concentrations in plasma are normally stable.

Question 14

How much does excreted creatinine compare to filtered creatinine?

Answer 14

F < E because you secrete 10%

Question 15

How is it possible that we can use blood tests to determine GFR?

Answer 15

there is a relationship between blood plasma and urine

Question 16

The relationship between GFR and plasma concentration of substance X is _____ (inversely, directly proportional) ____

Answer 16

Inversely proportional

Question 17

What is the downside to using creatinine levels as a measure of someone’s kidney health

Answer 17

Creatinine is going to be variable depending on someone’s muscle mass

Question 18

What is BUN?

Answer 18

Blood urea nitrogen (BUN)

This is a marker of muscle catabolism (blood urea, it contains nitrogen and you’re measuring the nitrogen)

Question 19

What is the downside to using BUN to measure GFR?

Answer 19

BUN values experience fluctuations depending on ingestion of protein during meals

Question 20

Because of the disadvantages to using BUN or creatinine to measure GFR on their own, how do we measure GFR using those values?

Answer 20

We take the BUN: Creatinine ratio which is generally a 10:1 ratio. If this ratio is high this is an indication that there is volumetric contraction

Question 21

Why should we have an understanding of renal blood flow?

Answer 21

It can help understand if something is an intra-renal or extra-renal issue

Question 22

How can we measure renal blood flow?

Answer 22

PAH clearance

It is freely filtered, but not reabsorbed. It is also secreted and most is excreted. Therefore, nearly all of it is cleared out of the plasma.

Question 23

To calculate true renal plasma flow, it is necessary to sample renal venous blood to measure plasma PAH concentration, which isn’t usually done. What do we measure to cancel out the venous sample and what is this?

Answer 23

Effective renal plasma flow - based on the amount we see in pee pee

Question 24

What is the filtration fraction?

Answer 24

Ratio between GFR and RPF ; it is the fraction of the RPF that is filtered by the glomerular capillaries. Normal filtration fraction is 20%, meaning 80% of the RPF is not filtered and enters via efferent arterioles into peritubular capillaries.

Question 25

What is the filtered load of any substance?

Answer 25

GFR x plasma concentration of substance X