Unit 4: Renal Phys. -- ion and Urea Handling by the Nephron/ H2O Balance

Question 1

What are the percentages for the Filtered load for the following ions?

1. Na+
2. K+
3. PO4^3-
4. Ca++
5. Mg++

Answer 1

1. 100%
2. 100%
3. 90%
4. 60%
5. 80%

Question 2

What ion has the lowest filtered load?

Answer 2

Ca++

Question 3

What ions has the highest filtered load?

Answer 3

Na+ and K+

Question 4

What ion has the most variability of excretion?

Answer 4

K+

Question 5

What ions are basically 100% reabsorbed?

Answer 5

Na+ and Ca++

Question 6

What ion has some reabsorption taking place in the Proximal Straight Tubule?

Answer 6

Phosphate

Question 7

What are all the locations that

Na+ is reabsorbed?

Answer 7

PCT– 67%
TAL – 25%
DCT – 5%
CD –3%

Excretion <1%

Question 8

What are all the locations that K+ is reabsorbed or excreted?

Answer 8

PCT – 67%
TAL – 20%
DCT/CD – only if low in diet

CD– variable excretion

Excretion varies 1-100%

Question 9

What are all the locations where phosphate is reabsorbed?

Answer 9

PCT – 70%
Proximal Straight Tubule– 15%**

Excretion ~15% (serves as buffer in urine for H+)

Question 10

What are all the locations that Ca++ is reabsorbed?

Answer 10

PCT – 67%
TAL – 25%
DCT – 8%

Excretion <1%

Question 11

What inhibits Na+ reabsorption in the DCT?

Answer 11

thiazide diuretics

Question 12

What inhibits Phosphate reabsorption in the PCT?

Answer 12

PTH

Question 13

What inhibits Ca++ reabsorption in the TAL?

Answer 13

Furosemide (loop diuretic)

Question 14

What stimulates Ca++ reabsorption in the DCT?

Answer 14

PTH

Thiazide diuretics

Question 15

What inhibits Mg++ reabsorption in the TAL?

Answer 15

Furosemide (loop diuretic)

Question 16

What are all the locations that Mg++ is reabsorbed?

Answer 16

PCT– 30% (lowest of all)
TAL– 60%
DCT– 5%

Excretion ~5%

Question 17

What two ions absorption are inhibited by Furosemide (loop diuretic in the TAL?

Answer 17

Ca++ and Mg++

Question 18

How much Urea is in the tubules prior to the PCT? What about after the PCT? What happens in the Thin descending limb?
How much urea is in the DCT? What happens in the CD?

Answer 18

prior to PCT-- 100%
after PCT -- 50%
Thin descending limb--> secreted
in DCT--> 110%
CD--> UT1 takes 70% urea out

Excretion id ADH present = 40%

(if no ADH– then all is secrete)

Question 19

What is important on the basolateral side in order to keep Na+ low in the cell so Na+ can come in passively on the luminal side?

Answer 19

Na+ K+ ATPase pump

Question 20

Where does most reabsorption take place?

Answer 20

in the proximal convoluted tubule

Question 21

What part of of the nephron is impermeable to H2O?

Answer 21

the Thick Ascending Limb

Question 22

Where is tubular fluid diluted in the nephron? Why?

Answer 22

in the Thick Ascending Limb b/c it is impermeable to water –> only solute can be pulled out of tubule and therefore dilutes urine

Question 23

What hormone increases K+ secretion by principal cells?

Answer 23

Aldosterone

Question 24

When there is an increase in plasma osmolarity due to water deprivation what gets stimulated and where?

Answer 24

stimulate osmole receptors in anterior hypothalamus

Question 25

During water deprivation, what will stimulation of osmole receptors in the anterior hypothalamus have of ADH?

Answer 25

increase ADH release--> therefore increase H2O permeability of principal cells (in DT and CD)--> will increase H2O reabsorption ---> therefore increasing urine osmolarity and decreasing urine volume--> decreasing plasma osmolarity toward normal

Question 26

During water deprivation, stimulation of osmole receptors in the anterior hypothalamus will cause the stimulation of what two things?

Answer 26

1. increase ADH release | 2. increase thirst

Question 27

What will too much H2O intake cause? and what will our body's response be?

Answer 27

decrease in plasma osmolarity--> inhibit osmole receptors in anterior hypothalmus

Question 28

What will the inhibition of osmole receptors in the anterior hypothalamus cause during H2O intake?

Answer 28

1. decrease ADH release | 2. decrease thirst

Question 29

What is the gradient of osmolarity in interstitial fluid from the cortex to the tip of the papilla?

Answer 29

Corticopapillary osmotic gradient

Question 30

What solutes contribute to the Corticopapillary osmotic gradient?

Answer 30

- NaCl | - Urea

Question 31

What mechanisms will deposit NaCl and Urea into the ISF to create the Corticopapillary osmotic gradient?

Answer 31

1. Countercurrent multiplication--> deposits NaCl in deeper regions 2. Urea Recycling --> deposits urea; a fxn of inner medullay CD

Question 32

What is the two step process for Countercurrent Multiplication? What are the two steps repeated until?

Answer 32

1. Single Effect 2. Flow of Tubular Fluid they are repeated until full corticopapillary gradient is established

Question 33

What does the size of the Corticopapillary gradient depend on? What is it in humans?

Answer 33

depends on length of loop on Henle 1200 mOsm/L at bend of juxtamedullary nephrons in humans

Question 34

What CREATES/establishes the corticopapillary gradient?

Answer 34

Countercurrent multiplication | two step process-- Single Effect and Flow of Tubular Fluid

Question 35

What helps MAINTAIN the gradient b/w the ISF and tubules?

Answer 35

Countercurrent Exchange

Question 36

What does the Single Effect step of the Countercurrent Multiplication refer to the function of?

Answer 36

to the function of the Thick Ascending Limb - here Na+ is reabsorbed via Na+K+2Cl- cotransporter - its activity is increased by ADH - TAL is impermeable to water and this dilutes fluid in TAL Recall: Descending limb is permeable to water Result: - osmolatrity in ISF and descending limb increases - osmolarity in ascending limb decreases

Question 37

Describe the "Flow of Tubular Fluid" step for Countercurrent Multiplication.

Answer 37

- there is continuous tubular flow entering the Proximal Tubule going to the Descending Limb that carries the osmolarity of 300 mOsm/L - this pushes down higher osmolarity tubular fluid toward bend in loop of Henle

Question 38

Give me the first four steps of Countercurrent Multiplication.

Answer 38

1. Single effect--> NaCl reabsorbed out of ascending limb and into ISF; increasing ISF osmolarity and diluting ascending limb tubular fluid; descending limb tubular fluid equilibrates w/ ISF 2. Flow of Fluid--> new fluid w/ 300 osmolarity enters DL from PT; fluid shifts; pushing high osmolarity of fluid down loop of Henle 3. Single effect--> NaCl reabsorbed out of ascending limb and into ISF;increasing ISF and descending limb's osmolarity; ascending limb further diluted 4. Flow of Fluid--> new fluid w/ 300 osmolarity enters again and pushes fluid

Question 39

What is the main point to why Countercurrent Multiplication works? (I.e. Single effect, flow of fluid, single effect, flow of fluid)

Answer 39

the ascending limb is impermeable to H2O | = diluting segment

Question 40

How does Urea recycling contribute to the conc. gradient?

Answer 40

- causes buildup of high conc. of urea in inner medulla - is secreted in Thin Descending Limb-- 110% of filtered load - TAL, DCT, cortical CT, outer medullary CD = impermeable to Urea - ---> therefore under ADH water is absorbed and urea left behind and that increase conc. of urea in tubule - UT1 in inner medullary CD is activated by ADH and will use facilitated diffusion to reabsorb 70% of Urea - therefore 40% filtered load is excreted (under ADH influence)

Question 41

How percentage of the filtered load of Urea is excreted under influence of ADH? How?

Answer 41

40% due to secreting 110% in Thin Descending limb and reabsorbing 70% via facilitated diffusion viw UT1 in inner medullary CD

Question 42

What are the capillaries that serve the medulla and papilla called? What type of nephrons are they specifically assoc. with? What are they involved with?

Answer 42

Vasa Recta; assoc. w/ juxtamedullary nephrons Countercurrent Exchange (NOT countercurrent mulitiplication)

Question 43

What is the Countercurrent Exchange?

Answer 43

- involves Vasa Recta in juxtamedullary nephrons - passive - helps MAINTAIN the gradient (NOT create it)

Question 44

What are the three cations that ADH has on the renal tubule?

Answer 44

1. increase H2O permeability of principal cells in late DT and CD 2. increase activity of Na+ K+ 2Cl- cotransporter in TAL--> enhancing size of osmotic gradient 3. increase urea permeability in inner medullary CD--> enhance Urea recycling and osmotic gradient (via UT1)

Question 45

How do we have production of Hyperosmotic Urine? What syndrome can cause this to occur?

Answer 45

- PCT = no change is osmolarity (300) - TAL = impermeable to H2O and reabsorb NaCl and dilutes tubular fluid - Early DCT --> reabsorbs NaCl and is impermeable to H2O - Late DCT--> presence of ADH causes Principal Cells permeable to H2O; and since tubular fluid is dilute, the H2O gets reabsorbed - CD-- H2O continues to be reabsorbed ~Syndrome of Inappropriate ADH (secrete too much ADH)

Question 46

How do we have production of Hyposmotic Urine? What condition may cause this?

Answer 46

- Low ADH (central diabetes) or ineffective ADH (nephrogenic diabetes) - Reabsorption in PCT is independent of ADH - TAL--> absorb NaCl and not H2O - Early DCT --> reabsorb NaCl and not H2O - W/o ADH; Last DCT and CD remain impermeable to H2O and some NaCl is reabsorbed; further diluting urine

Question 47

What areas of the nephron depend on ADH in order to become permeable to water and therefore reabsorb water?

Answer 47

Distal convoluted tubule and collecting duct

Question 48

What is defined as distilled water that is free of solutes?

Answer 48

Free Water Clearance

Question 49

In the nephron where is free water generated?

Answer 49

in diluting segment where solute is reabsorbed and water is left behind--> in the Thick Ascending Limb

Question 50

Measurement of free water clearance is a way to assess what?

Answer 50

assessing the kidney's ability to dilute or concentrate the urine

Question 51

When there is low ADH or it is ineffective, will the urine be hyposmotic or hyperosmotic? What will the free water clearance be, positive or negative?

Answer 51

all the free water generated in the TAL and early DCL is excreted b/c it cannot be reabsored by CD Urine = hyposmotic Free water clearance = positive (producing a dilute urine)

Question 52

When ADH is high, will the urine be hyposmotic or hyperosmotic? What will the free water clearance be, positive or negative?

Answer 52

all free water generated in TAL and early DCT will be reabsorbed by the last DCT and CD Urine = hyperosmotic Free water clearance = negative (therefore called "free water reabsorption")