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1

Cells of the body depend on..

A constant interstitial fluid concentration of solutes and osmolarity

-this is regulated by controlling the amount of extracellular water there is

2

Osmolarity is regulated by...

Water intake (thirst)

Renal excretion of water (glomerular filtration and reabsorption)

3

EDF osmolarity is about..

300 mOsm/L

4

Kidneys can excrete urine that ranges from..

50 mOsm/L - 1200 mOsm/L

5

How can the kidneys eliminate excess water?

How do they conserve water?

Can produce copious amounts of dilute urine

Can produce small amounts o concentrated urine

(Both can be done without changing excretion rates of solutes)

6

ADH regulates _____ (and therefore ___) ____ by controlling:

Plasma (and therefore interstitial) osmolarity

Water excretion

7

What happens what plasma osmolarity is increased?

Post pituitary ADH secretion increases

Then

Distal tubule H2O permeability increases

Then

Water reabsorption increases

8

As urine osmolarity changes, what happens to plasma osmolarity?

There is little to no change

9

Proximal tubule’s job in diluting urine

Solutes and water are reabsorbed at equal proportions (isosmotic)

10

Absorption of water in the descending loop of henle is due to:

a higher concentration of solutes in the renal medulla interstitium

11

The descending loop of henle concentrates what?

The tubular fluid (hyperosmotic)

12

In forming a dilute urine, what happens in the ascending loop of henle (thick)?

Reabsorption of electrolytes (Na+, K+, Cl) but not water

Dilutes tubular fluid (hyposmotic)

*this part of the loop is NOT permeable to water*

13

ADH is ____ in distal and collecting tubules when forming dilute urine. This means:

Absent

There is no reabsorption of water

14

The renal handling of water changes to form concentrated urine by the presence of:

ADH

15

What does ADH do in the distal and collecting tubules to H2O?

How?

Increases permeability to H2O

Causes reabsorption of water and a concentrated (hyperosmotic) urine

-since the renal medulla interstitium is hyperosmotic

16

A concentrated urine depends on _____ and:

ADH

A hypertonic renal medullary interstitium

17

Review slide 9

Slide 9

18

The most concentrated urine can be is:

1200 mOsm/L

19

The min amount o metabolic wastes and excess ions that must be eliminated bu the body to maintain homeostasis is about:

600 mOsm/day

20

The minimal amount of urine one must form a day is:

600/1200 = .05 L/day

21

What causes the renal medulla to become hyperosmotic ?

The countercurrent multiplier system

22

6 general steps of the countercurrent multiplier

1- the tubule fills with isosmotic fluid, with all transport systems/permeabilities off

2- ascending Limb pumps turned on— Increases osmolarity of the medulla

3- water permeability of the descending limb turned on. Causes equilibrium between the descending limb and the medulla interstitium (interstitium stays hyperosmotic bc the ascending pumps are still on)

4- tubular flow turned on. The hyperosmotic fluid that was in the descending limb moved to the ascending limb

5- the ascending limb still reabsorb solutes further concentrating the medially interstitium

6- the descending limb loses more water by osmosis again

*steps 4-6 are repeated to create a max gradient through the interstitium*

23

Review slide 15

Slide 15

24

What are impermeable to urea?

The ascending limb, distal tubule, and cortical collecting duct

25

What is permeable to urea? And what increases this?

Medullary collecting duct

ADH

26

As urine concentrates with ADH, ____ also concentrates, and is therefore (ACTIVELY/PASSIVELY) reabsorbed into the ____ contributing to:

Urea

Passively

Medullary

Medullary hyperosmolarity

27

Urea reabsorbed into the ___ ____ __ is secreted into the:

Therefore, urea:

Medullary collecting duct

Loop of henle

Recirculates increasing its concentration

28

In the presence of ADH, Urea recirculating (INCREASES/DECREASES), helping to maintain:

Increases

Hyperosmolarity of the renal medulla

29

In the absence of ADH, (MORE/LESS) urea is excreted

More

30

How much urea is remaining after passing through the loop of henle?

20%