Lecture 5- Renal Tubular Function Flashcards Preview

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Flashcards in Lecture 5- Renal Tubular Function Deck (29):
1

high water intake

excretion of dilute urine (50mOsm/L)

2

typical water intake

excretion of urine of normal osmolarity (500 mOsm/L)

3

low water intake

excretion of concentrated urine (120 mOsm/L)

4

reabsorption of water and solutes in proximal tubule is

iso-osmotic

5

In the thin descending limb there is increased water permeability so tubular osmolarity increases/decreases ?

increases- (due to high osmolarity of interstitial fluid in renal medulla drawing water out)

6

In the thick ascending limb, only solutes are absorbed so fluid is

hyposmotic

7

In the distal tubule and collecting duct, there is continued absorption of solutes, but not is water if ADH absent so

further ↓ in urine osmolarity

8

Diabetes Insipidus

-Patients either fail to make ADH or principal cells fail to respond to ADH
-Lack of production/response to ADH > excrete large volumes of urine (up to max excretion of 18L/day)

9

What is the maximal urine excretion a day?

18L/day
(10% of filtered water)

10

key factors in excretion of concentrated urine (2)

1. high osmolarity of medullary interstitium
2. high water permeability of DT and CD (from high ADH)

11

How much solute must you excrete a day?

600 mOsm (50% urea)
since mas osmolarity of urine is 1200 mOsm, the minimum volume excreted is 0.5L

12

High ADH - high water permeability of DT and CD will lead to

high water reabsorption

13

What does extensive water reabsorption in the DT and CD prevent?

excessive dilution of medullary intersitium

14

Urea is how much percent of max medullary osmolarity?

40% (500 mOsm/L) of the 1200 mOsm/L

15

What is urea?

a waste product from AA catabolism

16

How much urea do the kidneys need to clear?

25-35gm uea/day (50% of filtered urea is excreted

17

urea in PT

↑[urea] due to water reabsorption that's faster than urea

18

urea in thin loop of henle

↑[urea] due to high permeability & concentration in medullary interstitium

19

urea in thick loop of henle, DT, cortical CD

impermeable to urea
↑ ADH = ↑ water reabsorption from DT and CCD = ↑ [urea]

20

medullary CD

permeable to urea > urea diffuses into medullary interstitium

21

urea cycles from loop of henle back to medullary collecting duct maintains high/low concentration?

high

22

vasa recta

delivers blood to medulla without "washout" of solutes
Blood flow is slow (1-2% of total renal BF)

23

Countercurrent exchange

due to high permeability of vasa recta to solutes and water

24

Vasodilators

↑ BF > ↑ "washout" of solutes > ↓ ability to form concentrated urine

25

purpose of free water clearance

to determine whether water is excreted in excess of solutes or solutes are excreted in excess of water (relative to plasma)

26

Osmolar Clearance

volume of plasma cleared of solutes
C(osm) = U (osm) x V/P(osm)

27

Free water clearance

difference between urine flow rate and osmolar clearance
(can be positive or negative)

28

positive C(H2O)

water excretion > solute excretion

29

negative C(H2O)

water excretion < solute excretion