Exam 3 - Lecture 38 (Formation of Urine)

Question 1

What is osmolarity?

Answer 1

[ ] of osmotically active atoms per L/kg solvent.

Question 2

What is the normal osmolarity for canine ECF?

Answer 2

300 mOsm/kg

Question 3

What is an effective osmole?

Answer 3

A molecule that cannot cross a membrane and so generates osmotic pressure.

Question 4

In what osmolarity direction does water move?

Answer 4

Low –> high osmolarity

Question 5

What causes water to move across a membrane?

Answer 5

Presence of an osmolarity gradient

Question 6

What is an ineffective osmole?

Answer 6

Molecule that crosses a membrane and doesn’t contribute to tonicity.

Question 7

What happens during countercurrent multiplication at the Loop of Henle?

Answer 7

Fluid moves in opposite directions in each limb and thing happening in one limb amplifies what is happening in the other.

Question 8

What is the descending limb of the LoH permeable/impermeable to?

Answer 8

Permeable = H2O
Impermeable = Na+

Question 9

What is the ascending limb of the LoH permeable/impermeable to?

Answer 9

Permeable = Na+
Impermeable = H2O

Question 10

What is the osmolarity of the fluid leaving the PT?

Answer 10

isoosmotic

Question 11

What happens to interstitial osmolarity as you progress down the descending limb of the LoH?

Answer 11

Increases

Question 12

What is the osmolarity of the descending limb of the LoH vs. the interstitial fluid?

Answer 12

Lower

Question 13

What creates an osmotic gradient in the early DT?

Answer 13

ACTIVE reabs. of Na+

Question 14

How does water leave the descending limb of the LoH?

Answer 14

passively

Question 15

What happens at the hairpin?

Answer 15

Water has concentrated Na+ above interstitial [ ] so now there is an Na+ gradient; H2O reabs. stops

Question 16

How does Na+ leave the ascending limb of the LoH?

Answer 16

passively down its [ ] gradient

Question 17

How does Na+ leave the early DT?

Answer 17

actively

Question 18

What is the end result of the countercurrent multiplication in the LoH (2 things)?

Answer 18

1. Water and Na+ are reabs.

2. Hypotonic fluid delivered to DTs

Question 19

Which statement about the physiology at the LoH is true?

A) Na+ is reabsorbed passively at the descending limb
B) Water is reabsorbed down an osmolarity gradient (low to high osmolarity)
C) Interstitial osmolarity decreases towards papilla
D) Distal tubule fluid is hypertonic to interstitium

Answer 19

B) Water is reabsorbed down an osmolarity gradient (low to high osmolarity)

Question 20

Where is antidiuretic hormone produced?

Answer 20

Hypothalamus

Question 21

From where is ADH released?

Answer 21

Posterior pituitary gland

Question 22

What is the general role of ADH?

Answer 22

Determines whether kidney retains or expels water

Question 23

What are the 2 triggers for ADH release?

Answer 23

1. Changes in body fluid osmolarity

2. Changes is plasma volume or arterial pressure

Question 24

What are osmoreceptors and how do they react?

Answer 24

Bundles of cells that are very sensitive to changes in ECF osmolarity; will shrink when ECF osmolarity is too low = release of ADH

Question 25

What are baroreceptors and how to they react?

Answer 25

Specialized nerve cells sensitive to stretch; will trigger release of ADH when BP or volume is too low

Question 26

Where are baroreceptors found?

Answer 26

aortic arch and carotid sinus

Question 27

Where are osmoreceptors found?

Answer 27

hypothalamus

Question 28

What 2 things does ADH change?

Answer 28

1. Increases late DT and CT permeability to water thru aquaporins
2. Changes medullary (inner medulla only) CT permeability to urea (increases exp. of urea transporters in the luminal membrane)

Question 29

What is diuresis?

Answer 29

High production of urine/dilute urine; ADH is low/zero

Question 30

What happens to water in the DT and CT if ADH is low?

Answer 30

Cannot be reabs. so only way for it to go is down the CT and into the urine

Question 31

What is antidiuresis?

Answer 31

Low volume of concentrated urine produced; ADH is high

Question 32

What happens to water in the DT and CT if ADH is high?

Answer 32

Most water is reabs. thru aquaporins, so very little amount goes down CT into the urine.

Question 33

During diuresis, which of the following is true?

A) Medullary urea [ ] is relatively low
B) CT permeability to water is high
C) Water reabsorption in the descending limb of the loop is increased
D) Fluid in the CT is hypertonic to interstitium

Answer 33

A) Medullary urea [ ] is relatively low

Question 34

Urea is an _____ osmole at the CT. Why?

Answer 34

ineffective bc it does not affect water reabsorption.

Question 35

Urea is an _____ osmole at the descending limb of the LoH. Why?

Answer 35

effective bc H2O is reabsorbed more readily than normal when [urea] is high.

Question 36

The vasa recta preserves medulla _____.

Answer 36

hypertonicity

Question 37

What removes water that has been reabsorbed from the medullary CD and how?

Answer 37

vasa recta as a countercurrent multiplier

Question 38

During diuresis, which of the following is true?

A) A small volume of concentrated urine is produced
B) Urea permeability in medullary CD is low
C) Na+ is reabsorbed in descending limb of LoH
D) ADH levels are high
E) Water reabsorption in the CD is high

Answer 38

B) Urea permeability in medullary CD is low

Question 39

Mannitol can be used to change fluid retention in the kidney. It is freely filtered and acts as an effective osmole at the CD, increasing tubular fluid osmolarity. What happens to urine volume (ADH is present)?

A) It will increase
B) It will decrease

Answer 39

A) It will increase