Urine concentration and Dilution

Question 1

How much urine can the kidneys excrete a day? What is the lowest osmolarity of the urine?

Answer 1

20 L/ 50 mOsm

Question 2

What are the two portions of the nephron that are involved with the excretion of dilute urine?

Answer 2

Ascending thick limb of Henle and th eLAte distal convoluted tubule

Question 3

Describe the ascending thick limb of Henle

Answer 3

• absorbs sodium, potassium, and chloride
• impermeable to water
• more dilute as it flows up the tubule
• ADH does not effect

Question 4

Describe the late distal convoluted tubule

Answer 4

• reabsorb sodium chloride

- impermable to water in the absence of ADH

Question 5

What is the maximum urine concentration that the kidney can produce?

Answer 5

1200-1400 mOsm

Question 6

What are the two requirements for forming concentrated urine?

Answer 6

• presence of ADH

- high osmolarity of renal medullary interstitial tubule (establishes gradient)

Question 7

Why is there an obligatory volume of excreted urine of 0.5 L a day?

Answer 7

Because the maximum osmolality of the urine is about 1200 and the average human must secrete 600 mOsm of solute a day to get rid of the waste

600/1200=0.5 L/day
to get rid of the basic metabolic wastes that would otherwise be problematic

Question 8

Where in the kidney are most of the filtered electrolytes absorbed?

Answer 8

proximal tubule reabsorbs about 65%

Question 9

Describe the proximal tubule

Answer 9

65% of electrolytes
highly permeable to water
300 mOsm

Question 10

Describe the descending loop of Henle

Answer 10

-highly permeable to water
-less permeable to sodium chloride and urea
osmolarity increases to 1200 mOsm/L with high ADH

Question 11

Describe the thin ascending loop of Henle

Answer 11

• impermeable to water
• reabsorbs sodium chloride
• tubular fluid is more dilute
• urea diffuses into the ascending limb

Question 12

Describe the thick ascending loop of henle

Answer 12

• impermeable to water
• large amounts of sodium chloride, potassium, and other ions are transported in
• tubular fluid is dilute (100 mOsm)

Question 13

Describe the early distal tubule

Answer 13

• similar to the thick ascending loop of henle

- fluid is more dilute

Question 14

Describe the late distal tubule and cortical collecting tubule

Answer 14

osmolarity depends on ADH

urea is not permeant

Question 15

Describe the inner medullary collecting duct

Answer 15

osmolarity of the fluid depends on the ADH and surrounding intersititium osmolarity

Question 16

What are the portions of the nephron that are impermeable to urea?

Answer 16

Ascending thick limn of Henle and the distal cortical collecting tubule

Question 17

What happens in the cortical collecting tubule if ADH is increased?

Answer 17

water is reabsorbed and urea is not very permeant here and becomes more concentrated

Question 18

What happens in the medullary collecting duct if ADH is increased?

Answer 18

More water is reabsorbed form the medullary collecting duct
higher concentration of the urea
-diffusion of urea into the interstitial fluid

Question 19

What are the ADH activated transporters?

Answer 19

UT-A1 and Ut-A3

Question 20

What helps to maintain the high concentration of urea in the tubular fluid?

Answer 20

simultaneous movement of water and urea in and out of the inner medullary collecting duct

Question 21

What happens to the urine concentration if the ADH levels are low?

Answer 21

diluted urine

Question 22

What happens to the urine concentration if the ADH levels are high?

Answer 22

concentrated urine

Question 23

What prevents the medullary hyperosmolarity from being dissipated?

Answer 23

Vasa recta

Question 24

Describe the osmoreceptor-ADH feedback mechanism

Answer 24

• controls the extracellular fluid sodium concentration and osmolarity
• ADH is formed in the magnoceullluar neurons
• osmoreceptor cells

Question 25

What happens if there is and increased extracellular fluid osmolarity?

Answer 25

There is a shrinking of the osmoreceptor cells in the anterior hypothalamus which leads to increased action potentials which causes the release of ADH This increases water permeability in the distal nephron segment and the urine will be concentrated

Question 26

Where is ADH formed in the magnocellular nephron?

Answer 26

supraoptic nuclei and the paraventricular nuclei

Question 27

Where are the osmoreceptor cells?

Answer 27

In the vicinity of the AV3V region (anterior region of the third ventricle

Question 28

Describe the osmoreceptor feedback mechanism

Answer 28

1. water deficit 2. increased extracellular osmolarity 3. ADH secretion form the posterior pituitary 4. increased in the plasma ADH 5. Increased H2O permeability in the distal tubules and the collecting ducts 6. increased H2O reabsorption 7. decreased water is excreted 8. Concentrated urine

Question 29

Describe what happens to osmolarity and volume in isotonic volume depletion

Answer 29

osmolarity stays the same and volume decreases

Question 30

Describe what happens to osmolarity and volume in isovolumetric osmotic increase

Answer 30

volume is the same but the osmolarity increases

Question 31

What are the steps of the countercurrent multiplier system?

Answer 31

1. concentration in the loop of henle is the same 2. concentration is reduced because of the activation of an active ion pump pulling out solutes 3. concentration in the descending limb reaches osmotic equilibrium because of osmosis 4. hyperosmotic fluid flows into the ascending limb 5. More ions are pumped out fo the ascending limb (dilutes more) 6. Repeat steps 4-6 over and over again until we reach 7. equilibrium

Question 32

Which tubules are permeable to water?

Answer 32

descending

Question 33

Which tubules are impermeable to water?

Answer 33

ascending

Question 34

What is the overall role of ADH?

Answer 34

To make the tubules permeable to water by inserting aquaporins into the cellular membranes ALSO inserts urea transporters

Question 35

What is reabsorbed in the proximal tubule?

Answer 35

Water, NaCl and urea

Question 36

what is reabsorbed in the descending loop of henle when ADH is high

Answer 36

water

Question 37

What is reabsorbed in the ascending loop of Henle when AHD is high

Answer 37

NaCl

Question 38

What is reabsorbed in the medullary area when ADH is high?

Answer 38

Water, NaCL, urea | CONSERVING WATER

Question 39

What is reabsorbed in the proximal tubule when the ADH levels are low?

Answer 39

NACl and H2O

Question 40

What is reabsorbed in the descending loop when the ADH levels are low?

Answer 40

H20

Question 41

What is reabsorbed in the medullary region when the ADH levels are low?

Answer 41

NaCl, urine will be diluted

Question 42

Where does the urea that is reabsorbed from the medullary region go?

Answer 42

Goes to the loop of henle and is recycled into the tubular fluid

Question 43

What are the vasa recta?

Answer 43

Capillaries that parallel the loop of henle; water leaves the descending portion and inserts into the ascending limb help to maintain the equilibrium of the interstitial concentration differences

Question 44

True or false: the main purpose of the vasa recta is to supply blood to the nephron

Answer 44

False, they help to maintain the equilibrium of the concentration gradient

Question 45

Where is most of the change in the concentration of the urine occurring when there is increased ADH?

Answer 45

In the collecting tubule in the medullary region and the urine

Question 46

Does blocking the aldosterone system have an effect on the sodium intake and extracellular sodium concentrations relationships?

Answer 46

Nah