Medical Physiology Block 4 Week 2

Question 1

Is the kidney better at concentrating urine or diluting urine?

Answer 1

the kidney is better at diluting urine

Question 2

What is osmolal clearance? How do you compute osmolal clearance? what is the fixed value?

Answer 2

The amount of water cleared from the plasma, resulting in urine having the same osmolality as plasma; osmoles excreted per day/osmolality of blood (300 mOsmol/L); 2 L/day

Question 3

What is the product of urine osmolality and urine output?

Answer 3

osmoles excreted/day (under normal physiological conditions this is 600 mOsmol/day)

Question 4

What is free water clearance? How do you compute free water clearance?

Answer 4

The net amount of solute-free water moved from the blood to the urine; the difference between the urine volume and the osmolal clearance.

Question 5

Urine output is the sum of what?

Answer 5

sum of osmolal clearance and free water clearance

Question 6

What is the urine output for isosmotic urine?

Answer 6

osmolal clearance equals urine flow

Question 7

What is the mechanism for generating dilute urine? what is the free water balance?

Answer 7

the kidney generates free water in the tubule lumen by reabsorbing sodium (and its corresponding anions) in excess of fluid in segments of the nephron with low water permeability; positive free water clearance

Question 8

What is the mechanism for generating concentrated urine? what is the free water balance?

Answer 8

uses osmosis to drive water from the tubule lumen; negative free water clearance

Question 9

Does reabsorption of fluids and solute in the proximal tubule change the osmolalilty of the lumen?

Answer 9

No

Question 10

Are fluids or solutes more absorbed in the loop of Henle?

Answer 10

solutes; fluid entering the distal convoluted tubule is hypo-osmotic to blood

Question 11

Why is the countercurrent system important?

Answer 11

single effect produces a large gradient between the cortex and papilla

Question 12

What causes the single effect?

Answer 12

passive sodium chloride reabsorption in the tALH and active reabsorption in TAL; passive loss of water from tDLH

Question 13

How does the body concentrate urine?

Answer 13

during water depletion, AVP stimulates urea transporters in collecting duct increasing the gradient for water to move (during water diuresis, urea is excreted)

Question 14

What is countercurrent exchange?

Answer 14

hairpin structure of vasa recta (low blood flow to minimize washout of the medullary hypertonicity)

Question 15

Is carbon dioxide an acid or base?

Answer 15

acid

Question 16

What is the primary role of the kidney in acid/base balance?

Answer 16

Increase proton secretion and increase formation of bicarbonate

Question 17

If a patient is poorly ventilating what happens? how does the body compensate?

Answer 17

increased carbon dioxide decreases pH (more protons produced; respiratory acidosis); increased bicarbonate production

Question 18

If a patient has low plasma bicarbonate what is happening? how does the body compensate?

Answer 18

metabolic acidosis; increase ventilation

Question 19

How does the kidney concentrate protons?

Answer 19

titration with ammonium