Producing a concentrated or Dilute Urine

Question 1

What feature differentiates juxtamedullary nephrons from cortical nephrons?

Answer 1

Juxtamedullary nephrons have far longer loops of henle which stretch far deeper into the medulla

Question 2

What nephrons contain peritubular capillaries?

Answer 2

Cortical nephrons (surround all parts of the tubules)

Question 3

What percent of nephrons are juxtamedullary?

Answer 3

15%

Question 4

What does the blood from peritubular capillaries drain into?

Answer 4

Arcuate vein

Question 5

Where does the blood go in juxtamedullary nephrons from glomerulus and efferent arterioles?

Answer 5

• Forms long loops which follow loop of henle (vasa recta) only some reaches the medulla

Question 6

What does the vasa recta perfuse?

Answer 6

Loop of Henle and collecting duct that are in medulla

Question 7

What is the normal osmolarity of the extracellular fluid when entering the kidney?

Answer 7

300 mOsm/L

Question 8

What is the normal osmolarity of fluid when entering the distal convoluted tubule?

Answer 8

100 mOsm/L (due to reabsorption of ions)

Question 9

What happens to osmolarity after the DCT?

Answer 9

• Further reduced in DCT and collecting ducts due to additional reabsorption of NaCl.
• In abscence of ADH CDs are impermeable to water and tubular fluid becomes even more dilute to as low as 50 mOsm/L

Question 10

What does the thin descending limb transport?

Answer 10

Water (impermeable to salts)

Question 11

What diuretic acts on the thin descending limb?

Answer 11

Loop diuretics (furosemide) (most powerful)

Question 12

Where in the loop of henle is water uptake?

Answer 12

• Thin descending limb

No water can be absorbed in the thin and thick ascending limbs

Question 13

What is the symporter of the thick descending limb called?

Answer 13

Na+/K+/2Cl-

Question 14

What is the main symporter on the distal collecting tubule?

Answer 14

Na+/Cl-

Question 15

What is the osmolarity of tubular fluid leaving the loop of henle into the DCT?

Answer 15

100 mOsm/L

Question 16

What happens to the osmolarity of the tubular fluid in the DCT?

Answer 16

Falls due to continual removal of ions

Question 17

What is the water reabsorbtion dependant on in the cortical section of the Collecting ducts?

Answer 17

ADH levels

Question 18

Where is the water transported into after the cortical section of the collecting ducts?

Answer 18

Cortical peritubular capillaries (not vasa recta from juxtamedullary nephrons)

Question 19

Where is the osmotic gradient in the medulla maintained?

Answer 19

Through awater absorption in the kidney cortex

Question 20

What percentgae of blood flow is to the cortex?

Answer 20

90%

Question 21

What percentage of filtered urea is reabsorbed in the PCT?

Answer 21

40-50% (concentration in tubular fluid rises though as it is less than that of water)

Question 22

Describe urea recirculation

Answer 22

• High concentration of urea causes it to move out of the medullary collecting ducts into the medullary interstitial fluid
• Facilitated by specific urea transporters. One of these transporters is activated by ADH so enhancing the movement of urea out of the medullary collecting duct into the medullary interstitial fluid
• A moderate amount of this urea can move back into the tubule at the inner medullary section of the loop of Henle and so can recirculate through the tubule distal to this part of the nephron several times
• This recirculation can contribute to the concentration of urea in the distal tubular fluids in times of dehydration
• The urea recirculation also provides an additional mechanism for the formation of the hyperosmotic renal medulla
• In full hydration where waater is to be lost, then tubular flow is greater and this recirculation of urea is less marked and contributes less

Question 23

What is the main osmolite in the medulla?

Answer 23

Urea

Question 24

What is the main activator of urea transporters?

Answer 24

ADH

Question 25

What is the normal concentration of urea in the blood?

Answer 25

4.5mmol

Question 26

What percentage of renal blood flow is to the medulla?

Answer 26

5%

Question 27

Does more fluid enter or leave the vasa recta?

Answer 27

Enter