102914 clinical corre renal physio

Question 1

how is isotonicity maintained?

Answer 1

if hypotonicity (in the case of the woman drinking too much water in a contest), the response in the body is to inhibit hypothalamic receptors, then

decrease ADH release, increasing renal water excretion
AND
decrease thirst, decreasing water intake

Question 2

what are the stimuli for ADH release?

Answer 2

osmoreceptor control (plasma osmolarity)
baroreceptor control (percent of blood volume depletion)

Question 3

urine osmolarity can vary a wide range due to?

Answer 3

ADH

Question 4

what is the primary determinant of ECF osmolarity?

Answer 4

serum Na

Question 5

how is ECF osmolarity regulated?

Answer 5

changes in thirst and ADH secretion

Question 6

is BUN or creatinine more accurate at indicating GFR?

Answer 6

creatinine

BUN is a product of prtotein metabolism and it can vary due to protein intake, catabolic rate, tubular reabsorption

Question 7

serum creatinine

Answer 7

breakdown product of skeletal muscle
production remains constant over time
filtered at glomerulus like inulin and can be used to estimate GFR
serum levels are inversely proportional to GFR

Question 8

what is the limitation of creatinine in assessing GFR?

Answer 8

unlike inulin, creatinine is also secreted in nephron and creatinine clearance overestimates GFR

Question 9

how does GFR change in relation to serum creatinine changes?

Answer 9

at lower end of serum creatinine levels, GFR changes are larger

Question 10

how can you calculate creatinine clearance to assess GFR?

Answer 10

UV/P

Cockcroft Gault eqn

Question 11

how can GFR be calculated from serum creatinine?

Answer 11

100/serum creatinine is approximately GFR

Question 12

how can serum creatinine based GFR assessments be inaccurate?

Answer 12

extremes of age
BMI
muscle mass differences (if pt is very heavy, GFR will be underestimated)

Question 13

what happens with ECF contraction/volume depletion?

Answer 13

decreased effective circulating volume
baroreceptor activation
increased sympath tone

see slide- angiotensin II, aldosterone, ADH (baroreceptor)

Question 14

Na reabsorption via angiotensin II vs aldosterone

Answer 14

angiotensin II likely plays a greater role because it’s at proximal tubule, whereas aldosterone is in cortical collecting duct principal cells

Question 15

endocrine fxns of kidney

Answer 15

renin
erythropoeitin
1,25 dihydroxyvitamin D (proximal tubule cells)

Question 16

chronic kidney disease’s impact on calcium and phosphorous

Answer 16

decreases 1,25 D (calcitriol)
increases serum phosphorous (increased retention)

both lead to decreased serum Ca

all of these lead to increased PTH, which leads to increased bone turnover and extraosseous calcifications