Elements of Renal Function

Question 1

What are the primary driving forces for increases or decreases in filtration?

Answer 1

Changes in glomerular hydrostatic pressure OR pressures in Bowman’s space (disease state)

Question 2

What is the primary driving force for increased or decreased reabsorption into peritubular capillaries?

Answer 2

Changes in capillary hydrostatic pressure due to changes in RBF

Question 3

How does exercise affect RBF?

Is this good?

Answer 3

Decreases, since it’s shunted away to the muscles

Can be dangerous to kidneys if too much

Question 4

How does blood flow change in the different regions of the kidney?

Why?

Answer 4

Decreases the deeper you get

Medulla needs slower flow so that concentrated ions, etc. are not washed away

Question 5

A patient has consistent increased blood flow to the medulla of the kidneys. How will this affect its ability to concentrate urine?

Answer 5

Decreased - the gradient in the medulla will be washed out due to increased blood flow to the medulla

Question 6

A patient drinks a lot of hypotonic water. How will this affect:

GFR?
Peritubular Starling forces?
Reabsorption?

Answer 6

GFR constant (autoregulation)

Cap. hydro pressure UP (more fluid in capillary)

Reabsorption DOWN (Starling ∆)

Question 7

What are neurohormonal reflexes?

Answer 7

Changes in sympathetic discharge and hormone release based on changes in blood volume and osmolarity

Question 8

2 main sensors that cause downstream regulation?

Where are each?

Answer 8

Volume receptors (R. atrium)

Osmoreceptors (brain)

Question 9

An increase in blood volume will cause what sympathetic changes?

Answer 9

Decreased discharge - increased urination, decreased ADH, decreased RAAS, decreased thirst, decreased reabsorption

Question 10

Sympathetic discharge on the kidney will have what 4 main effects?

Answer 10

Decreased GFR
Increased PCT reabsorption
Increased DCR reabsorption
Increased thirst (Ang 2)

Question 11

The overall effect of sympathetic discharge on the kidney is what?

Due to what 3 things?

Answer 11

Fluid and electrolyte retention

Decreased urination
Decreased Na excretion
Increased water intake

Question 12

If sympathetic discharge causes afferent constriction, what will be the effects on RBF and GFR?

Compensation?

What about reabsorption? Why?

Answer 12

RBF will decrease, so GFR will decrease

Ang2 causes efferent constriction, returning GFR to normal

Sympathetics cause renin release (granular cells), stimulating Na (and thus H2O) reabsorption (aldosterone) in the PCT, TAL, DCT, and CD - INCREASED B.V.

Question 13

How are sympathetics stimulated in the kidney?

What are the downstream affects on reabsorption?

Answer 13

Drop in volume receptor activation
Vagus n. to vasomotor center
Sympathetic stimulated there

Increased RAAS, so increased aldosterone, so increased reabsorption

Question 14

How to calculate urinary excretion volume?

Answer 14

F + S - R
Urinary excretion = amount filtered – amount reabsorbed
+ amount secreted

Question 15

Definition of GFR

How does this relate to RBF?

Answer 15

Volume (mL) of plasma filtered into the kidneys per minute

Normally 20% of RBF, but only partially dependent on RBF

Question 16

Definition of filtration rate

Calculate?

Answer 16

Amount of a given substance filtered per unit time

GFR x plasma [ ]
Filtration rate (Filtered load) of any freely filtered
substance = GFR x plasma concentration of substance

Question 17

Urinary excretion rate

Calculate?

Answer 17

Amount of a substance excreted per unit time

Urine [ ] x urine volume (V)

Question 18

Renal clearance

Calculate?

Used how?

Answer 18

Volume of substance from which a given substance is completely cleared in a given time

Urinary excretion rate / plasma [ ]

Measures renal function and GFR

Question 19

How can GFR be related to clearance?

Answer 19

The clearance of substances freely filtered and neither metabolized, secreted, or reabsorbed = GFR

Question 20

Why is creatinine better than inulin?

Answer 20

Creatinine is endogenous and consistently made by skeletal muscle

Question 21

How is creatinine concentration related to GFR?

Answer 21

Inversely related

If GFR goes up, clearance of it is going up, so plasma concentration is down

Question 22

Why is the inverse relationship between creatinine [ ] and GFR not perfect?

Answer 22

Some creatinine will undergo compensatory secretion in the PCT

Question 23

What is the idea behind the BUN/Cr ratio?

Answer 23

Both are freely filtered, but only BUN is reabsorbed and can be regulated, making its concentration much higher and variable in the blood

Question 24

A ratio of >20:1 means what?

Answer 24

There is more BUN in the blood than normal, thus the patient is dehydrated OR blood is not getting to the kidney for filtration

PRE-RENAL

Question 25

A ratio of

Answer 25

BUN is not being reabsorbed properly OR is being overly filtered due to a glomerular issue

INTRA-RENAL

Question 26

A ratio between 10:1 and 20:1 means what?

Answer 26

Either the patient is normal…

OR urine is not being excreted due to a downstream block

POST-RENAL / NORMAL

Question 27

What is the use of PAH?

Answer 27

Freely filtered but AVIDLY secreted in PCT

PAH clearance = RPF since ALL is excreted, especially in smaller [ ]’s

Question 28

Filtration Fraction

A higher FF means what?

Answer 28

GFR/RPF

Less fluid in efferent arteriole, so higher oncotic pressure, so more reabsorption