Urine concentration/dilution

Question 1

Where is ammonium converted to urea?

Answer 1

Liver

Question 2

How do we measure [urea] in the US?

Answer 2

BUN = mg/dL

Question 3

Why is it that on a short term basis, urea excretion may not match the production rate?

Answer 3

Urea is needed in the regulation of water

Question 4

What happens to urea in the proximal tubule? Loop of henle?

Answer 4

50% Reabsorbed in the proximal tubule

About same amount as above secreted in the loop of henle

Question 5

What produces NH4 in the body?

Answer 5

Protein catabolism

Question 6

Why do we reabsorb urea in the proximal tubule and collecting duct, only to secrete a very similar amount in the loop of henle?

Answer 6

Helps to create a hyperosmotic area in the renal medulla

Question 7

What is significant about the loop of henle as far as transporters go?

Answer 7

Has active urea transporters

Question 8

What happens to the [urea] as you move from the proximal tubule to the end of the loop of henle?

Answer 8

increases

Question 9

The amount of urea reabsorbed by the collecting duct is dependent on what? Why?

Answer 9

[ADH], since ADH activates a urea transporter

Question 10

About 40% of the urea that was filtered is excreted. Where did the rest go?

Answer 10

• ~10% enters the vasa recta

* ~50% enters the loops of Henle

Question 11

To produce concentrated urine the kidney needs what two things?

Answer 11

ADH and a hyperosmotic renal medulla

Question 12

The loops of Henle act as what (as far as countercurrent exchange goes)?

Answer 12

Countercurrent multipliers

Question 13

The vasa recta act as what (as far as countercurrent exchange goes)?

Answer 13

Countercurrent exchangers

Question 14

What are the relative permeabilities to water of the thin descending loop, thin ascending loop, and thick ascending loop?

Answer 14

Thin descending loop is permeable

Thin and thick ascending are not permeable

Question 15

What is occurring in the thick limb of the tubule?

Answer 15

secondary active transport to move Na+ and C1- out of the tubule and K+ back in

Question 16

The thick limb (which is impermeable to water) pumps Na and Cl out in exchange for a K in. What is the consequence of this?

Answer 16

K+ movement inwards causes the lumen to become positively charged, forcing cations out of the lumen, and diluting the filtrate

Question 17

What is Bartter syndrome?

Answer 17

A genetic disease in which Na reabsorption in the thick limb is impaired, (d/t loss of Barttin protein) leading to a chronic loss of Na, Mg, as well as metabolic acidosis

Question 18

The greater the length of the loop of Henle, the (BLANK) the osmolality that can be reached at the tip of the medulla.

Answer 18

The greater the length of the loop of Henle, the GREATER the osmolality that can be reached at the tip of the medulla.

Question 19

Juxtamedullary nephrons have longer loops of Henle and spread the gradient over a longer distance. What is the effect of this?

Answer 19

The greater the length of the loop of Henle, the greater the osmolality that can be reached at the tip of the medulla.

Question 20

What is the overall effect of the nephron countercurrent exchanger? (this is a longer answer probably not suitable for a notecard, but whatevs)

Answer 20

High osmolality of the interstitium allows water from new filtrate to flow into the interstitium, causing hyperosmolality of the filtrate.

Since the filtrate is hyperosmotic to plasma, ions tend to flow out after it leaves the descending limb, but water is prevented from following d/t the walls of the ascending loop. Thus we can remove water from the remaining filtrate in the collecting duct easily d/t this high osmolality of the interstitium

Question 21

Too much blood flowing through the kidney medulla could wash out the gradient. How is this prevented? (2)

Answer 21

1. Minimal blood entering the peritubular capillaries

2. Countercurrent in the vasa recta

Question 22

What is the countercurrent utilized by the vasa recta?

Answer 22

1. As blood travels down, lose water, gain ions

2. As blood goes up, lose ions, gain water

Question 23

What is the MOA of ADH?

Answer 23

Adds aquaporins to the collecting duct via V2 receptor and G protein

Question 24

What is the osmolality of the filtrate at each of the major areas in the nephron (assume Proximal tubule = 1) [descending, ascending, collecting duct]

Answer 24

Descending = 1 or slightly >1

Ascending = <>1 if ADH present

Question 25

What is diabetes insipidus? (2)

Answer 25

Either a lesion in the hypothalamus (central DI) or a problem with recruitment of aquaporins (nephrogenic DI)

Question 26

What are the factors that control ADH release?

Answer 26

BP via baroreceptors

Volume via Atrial stretch receptors

Question 27

Baroreceptors fire in response to what? Where does this signal go? What does this cause?

Answer 27

Fire in response to increased BP.

Goes to NTS.

Less firing causes ADH release and v.v.

Question 28

Which generates a stronger ADH response, a change in blood osmolality or volume?

Answer 28

osmolality

Question 29

What happens to baroreceptors in pts who are confined to a bed?

Answer 29

there is a gradual shift of fluid from the legs to the abdomen, thorax and head. This would increase venous return to the heart and raise the blood pressure in the atria.

Thus increase urine excretion

Question 30

What are the two drugs discussed in class that increase ADH?

Answer 30

1. Morphine

2. Nicotine

Question 31

What is the one drug discussed in class that decreases ADH?

Answer 31

Ethanol

Question 32

Above what plasma osmolality does the thirst response kick in? What causes this to occur?

Answer 32

280 mOsm/kg H2O

Caused by plasma AVP (ADH)

Question 33

What is the relationship between plasma osmolality and [ADH]

Answer 33

Linear

Question 34

What is the relationship between blood volume and [ADH]

Answer 34

Parabolic (kinda)

Question 35

What is the effect on angiotensin II as far as thirst goes?

Answer 35

Increases via stimulating the hypothalamus

Question 36

Why do people with a high protein diet have an increased ability to concentrate their urine?

Answer 36

Increases urea deposition in the medullary interstitium means there is a higher osmolarity gradient

Question 37

Why do patients with Barrett’s syndrome end up with hypomagnesemia and hypokalemia?

Answer 37

Cannot transport Mg or other ions if the Na gradient is not established

Question 38

What does dehydration do to the rate of sympathetic nerve firing?

Answer 38

Increases (don’t know how)