Clinical Correlates of Renal

Question 1

Why is water homeostasis important?

What are baseline sodium and potassium in ECF?

Answer 1

Regulation of osmolarity

Sodium = 140 mEq/L
Potassium = 4 mEq/L

Question 2

What are the two stimuli for ADH release?

What is the range of urine osm due to ADH?

Answer 2

Plasma osmolarity (increased Osm results in increased ADH)
Baroreceptor measurement of volume depletion (depleted volume results in increased ADH)

50 to 1200

Question 3

What determins significance of hyponatremia?

What is the clinical manifestations of hyponatremia?

Answer 3

Prominent in rapid change in water

Non specific signs and symptoms (Nausea, vomiting, weakness, headache, siezure, RDS, death)

Question 4

1. What appropriately elevates ADH?
2. What can result in excessive water intake?
3. What cna result in altered renal water handling?
4. What can cause inappropriate secretion of ADH?

Answer 4

1. Volume depletion
2. Hypotonic fluids, other irrigants
3. CKD
4. Cancer (small cell lung e.g.), CNS dz, Pul dz, Drugs (narcotics, antiemetics, SSRIs), HIV

Question 5

What are the formula for creatinine clearance?

Answer 5

Creatinine Clearance = U_Creat * U_Vol/(P_Creat)

**Cockcroft-Gault Estimate: **Creatinine Clearance = ((140-age) * Weight (kg))/(Serum Cr * 72) * 0.85 (if female)

Creatinine clearance is always in mL/min

Question 6

What is GFR? What is the range?

Answer 6

Amount of plasma filtered through glomeruli per unit time (90-125 mL/min)

Question 7

What is the blood urea nitrogen?
How accurate of a GFR indicator is it?
What is it used for?

Answer 7

Nitrogenous waste product of protein metabolism
Less acrruate than creatinine due to variation in protein intake, catbolic rate, tubular reabsorption
Used to help diff dx with creatinine in renal dz

Question 8

What is serum creatinine?
What can it be used to estimate?

Answer 8

Breakdown product of skeletal muscle
Production remains constant over time
Serum levels are inversely proportionate to GFR (~100/Cr)

Question 9

What influences tubular Na reabsorption?

Answer 9

Renal sympathetic tone
Hormones
BP

Question 10

What is the direct tubular effect of renal sympathetic nerves?
Of Angiotensin II?

Answer 10

Renal SNS - Multiple tubular receptors stimulate Na reabsorption
AngII - Tubular receptors, increases activity of the PT Na/H countertransporter

Question 11

What is aldosterone’s effect on Na reabsorption?

Answer 11

Stimulates Na reabsorption in cortical collecting duct principal cells
~2% of filtered load of Na has its excretion dependent on aldosterone action
Increases number of luminal Na channels and BL Na/K-ATPases

Question 12

What controls aldosterone secretion?

Answer 12

Angiotensin II is most important stimulus relating to Na balance

Question 13

What is the mechanism of action of ADH?

Answer 13

ADH binds to V2 which activates adenyl cyclase, increasing cAMP in the cell
cAMP leads to PKA cascade which leads to AQP2 insertion to the lumen of cell
AQP2 responsible for water reabsorption

Question 14

What is the endocrine function of renin?
What is the endocrine function of erythropoietin?
What is the endocrine function of 1,25 dihydroxyvitamin D production?

Answer 14

**Renin **- Secreted by juxtaglomerular cells
Converts angiotensinogen to angiotensin, regulating BP and salt balance

**Erythropoetin (epo) **- Produced by renal cortical tubular cells, stimulates erythrocyte production in marrow

**1,25-dihydroxyvitamin D - **Formed in PT cells, regulates calcium and phosphate balance

Question 15

What is the effect of CKD on calcium and parathyroid hormone?

Answer 15