Exam 3 Lecture: Formation of Urine

Question 1

What does osmotically active mean?

Answer 1

the solute contributes to generating an osomotic pressure = it will cause osmosis

Question 2

What do osmolarity differences drive?

Answer 2

water movement in the loop, distal tubule, and collecting duct

Question 3

At any point in the descending limb, how is the osmolarity in the tubular fluid related to the interstitia surrounding it?

Answer 3

The osmolarity of the tubular fluid is always lower than the osmolarity of the interstitia surrounding it

Question 4

What direction does water move in the descending limb?

Answer 4

water passively moves out of the descending limb

Question 5

At any point in the ascending limb, how is the Na concentration in the tubular fluid related to the interstitia surrounding it?

Answer 5

the sodium concentration in the tubular fluid is always higher than the sodium concentration of the interstitia

Question 6

What direction does sodium move in the ascending limb?

Answer 6

Na moves out of the ascending limb

Question 7

What creates the osmotic gradient in the descending limb?

Answer 7

active reabsorption of Na in the early distal tubule

Question 8

What is the active reabsorption of Na in the early distal tubule done by?

Answer 8

NKCC1

Question 9

What occurs at the hairpin loop?

Answer 9

the osmolarity of the tubular fluid equals the osmolarity of the interstitium; the solutes creating the osmolarity is not the same

Question 10

What is the high tubular fluid osmolarity in the hair pain due to?

Answer 10

Na

Question 11

What is the high intersitial osmolarity in the hair pin due to?

Answer 11

Na and urea

Question 12

What is the sodium concentration like at the distal straight tubule?

Answer 12

Na inside equals Na on the outside which is where NKCC1 comes into play

Question 13

What is the tubular fluid like in the distal straight tubule?

Answer 13

hypotonic

Question 14

What happens when there is no/low levels of ADH?

Answer 14

diuresis and water is expelled from animal urine

Question 15

What happens when there are high levels of ADH?

Answer 15

antidiuresis and water is conserved by animal; water is reabsorbed back to blood and not wasted in urine

Question 16

What are the stimuli for ADH release?

Answer 16

ECF osmolarity and ECF volume

Question 17

What is a high ECF osmolarity sensed by?

Answer 17

osmoreceptors

Question 18

What does high ECF osmolarity trigger?

Answer 18

the release of ADH

Question 19

What is a low ECF volume sensed by?

Answer 19

baroreceptors

Question 20

What does low ECF volume trigger?

Answer 20

ADH release

Question 21

What are the functions of ADH?

Answer 21

changes collecting duct permeability to water, changes medullary collecting duct permeability to urea

Question 22

How does ADH make collecting ducts more permeable to water?

Answer 22

it increases the expression of water channels in the luminal membrane of the epithelium

Question 23

In the loop, why and where is water reabsorbed?

Answer 23

in the descending loop due to high interstitial osmolarity caused by Na and urea

Question 24

In the loop, why and where is Na reabsorbed?

Answer 24

in the ascending limb due to the concentration gradient established by water reabsorption

Question 25

Without ADH what happens?

Answer 25

no water is reabsorbed in either the distal tubules or collecting ducts

Question 26

How does low ADH relate to ECF volume and ECF osmolarity?

Answer 26

reduces ECF volume, increase ECF osmolarity

Question 27

How does high ADH relate to ECF volume and ECF osmolarity?

Answer 27

increases ECF volume, decreases ECF osmolarity

Question 28

How much urine is created when ADH is present and is it diluted or concentrated?

Answer 28

a small amount of concentrated urine and high osmolarity

Question 29

What is the role of urea?

Answer 29

to act as an effective osmole at the loop

Question 30

In the distal tubule, what is the urea concentration like in the tubule vs the interstitia surrounding it?

Answer 30

the urea concentration in the tubule is higher than in the interstitia surrounding it creating a urea concentration gradient

Question 31

What effect does ADH have on the diffusion of urea?

Answer 31

it allows passive diffusion to occur

Question 32

Where is urea an ineffective osmole?

Answer 32

in the collecting duct

Question 33

Where is urea an effective osmole?

Answer 33

in the loop

Question 34

What does the increased interstitial urea concentration in the loop do?

Answer 34

increases the interstitial osmolarity around the loop, draws even more water out than normal, and leads to an even lower volume of concentrated urine being produced

Question 35

What mechanisms make sure urea does not keep accumulating in the interstitum?

Answer 35

• ADH levels are reduced so urea does not accumulate
• ascending limb is kind of permeable to urea so it can move into the ascending limb and be recycled
• vasa recta is permeable to urea and can cycle it away

Question 36

What is the vasa recta?

Answer 36

straight arterioles adjacent to the loop of Henle

Question 37

What would happen if water that was reabsorbed into the interstitium at the loop and collecting duct were to stay?

Answer 37

it would dilute osmotic gradient and impair renal function

Question 38

What is the goal of the vasa recta?

Answer 38

to remove water from the interstitium and keep Na in the interstitium

Question 39

What is the difference between the loop of henle and the vasa recta?

Answer 39

The descending and ascending limb are both permeable to Na and H20 of the vasa recta

Question 40

Since water is permeable in the ascending limb of the vasa recta, what does that mean?

Answer 40

water moves down the osmotic gradient into the ascending limb and is carried away from the medulla into the bloodstream

Question 41

Since Na is permeable in the descending limb of the vasa recta, what does that mean?

Answer 41

Na can move into the descending limb if it wants to, so it does which allows Na to constantly circulate around the medulla