Costanzo Renal Physiology: NaCl regulation

Question 1

What is tubular fluid?

Answer 1

urine at any point along the nephron

Question 2

What does it mean if the tubular fluid : plasma concentration ratio is 1 for any given filterable substance?

Answer 2

It means that the there has been no reabsorption of the substance in the kidney or that the reabsorption is equal to the reabsorption of water.

Question 3

What does a TF/P ratio of less than one mean?

Answer 3

A TF/P ration of less than one means that the reabsorption of the substance is greater than the reabsorption of water.

Question 4

What does a TF/P ratio greater than 1 mean?

Answer 4

A TF/P ration of greater than one means that the reabsorption of the substance was less then the reabsorption of water or it has been secreted.

Question 5

Why is the TF/P ratio of inulin used to determine water reabsorption?

Answer 5

inulin is not reabsorbed or secreted therefore its concentration in the urine is completely dependent on how much water is in the tubules. This means that water reabsorption alters the concentration of insulin in the urine.

Question 6

What is the equation for water reabsorption?

Answer 6

Fraction of reabsorbed water = 1- ( 1 / [TF/P]in )

Question 7

How is the fraction of filtered load in the tubule determined for a given substance?

Answer 7

The TF/P ratio for the subtance is divided by the TF/P ratio for inulin to correct for water reabsorption.

Question 8

Can Na+ be filtered by the glomerulus?

Answer 8

Yes Na+ can pass freely through the glomerular barrier.

Question 9

Is Na+ highly excreted?

Answer 9

No! Na+ is not excreted in large amounts (<1%) because it is reabsorbed along the entire length of the nephron.

Question 10

What proportion of the water and sodium is reabsorbed in the proximal tubule?

Answer 10

About 67% of the water and Na+ is reabsorbed in the proximal tubule. (isosmotic reabsorption keeps the Na+ TF/P at 1 in the proximal tubule)

Question 11

What proportion of the Na+ is reabsorbed in the thick ascending limb?

Answer 11

About 25%

Question 12

What proportion of Na+ is reabsorbed in the distal convoluted tubule?

Answer 12

about 5%

Question 13

What proportion of the Na+ is reabsorbed in the collecting duct?

Answer 13

about 3%

Question 14

How does the early poximal tubule reabsorb Na+?

Answer 14

The early proximal tubule reabsorbs Na+ by co-transport with
(1) glucose
(2) amino acids
(3) phosphate
(4) lactate
And also by the counter transport with H+, where HCO3- and Na+ are absorbed and H+ is secreted.

Question 15

What is the function of carbonic anhydrase inhibitors (acetazolamide)?

Answer 15

They are diuretics that inhibit the reabsorption of HCO3- in the early proximal tubule.

Question 16

How is Na+ reabsorbed in the late proximal tubule?

Answer 16

Na+ is reabsorbed with Cl- in the late proximal tubule.

Question 17

What is Glomerulotubular balance?

Answer 17

Glomerulotubular balance reflects the proximal tubules ability to maintain a constant fractional absorption of Na+ of 67%.

Question 18

How is glomerulotubular balance achieved?

Answer 18

glomerular filtration increases the protein concentration of the peritubular capillaries. This increased protein concentration generates the oncotic pressure that drives the reabsorption of isosmotic fluid (water and Na+) into the peritubular capillaries. In this sense the Starling forces in the glomerulus are what drive the reabsorption of water and Na +

Question 19

What effect does ECF volume contraction have on proximal tubule reabsorption?

Answer 19

volume contraction will increase the peritubular protein concentration (increased oncotic pressure) and decrease the peritubular hydrostatic pressure. This combination will result in increased reabsorption in the proximal tubule.

Question 20

What effect will ECF volume expansion have on proximal tubule reabsorption?

Answer 20

ECF volume expansion will cause a decrease in peritubular protein concnetration and an increase hydrostatic pressure. These increased starling forces will decrease reabsorption in the proximal tubule.

Question 21

How is Na+ transported in the thick ascending loop of Henle?

Answer 21

Na+, K+, 2Cl- co-transporters in the luminal membrane are responsible for reabsorption in the thick loop of Henle.

Question 22

What drugs inhibit the Na+, K+, 2Cl- co-transporters in the thick ascending loop of Henle?

Answer 22

The loop diuretics (furosemide, ethacrynic acid, bumetanide)

Question 23

What is the TF/P ratio for Na+ in the thick ascending loop of Henle?

Answer 23

The TF/P ratio for Na+ is <1 in the thick ascending loop of Henle since the loop is impermeable to water. (diluting segment)

Question 24

Why is the lumen of the thick ascending loop electrically positive?

Answer 24

Some K+ leaks back into the lumen through the Na+, K+, 2Cl- co-transporter.

Question 25

How does the early distal tubule reabsorb Na+?

Answer 25

By NaCl co-transporters.

Question 26

What drugs act at NaCl co-transporters in the early distal tubule?

Answer 26

Thiazide diuretics.

Question 27

What effect does the early distal tubule have on the TF/P of Na+?

Answer 27

The TF/P of Na+ is further reduced in the distal tubule because like the thick ascending loop it is impermeable to water. (cortical diluting segment)

Question 28

What are the two special features of the late distal tubule and collecting ducts?

Answer 28

(1) principal cells

(2) Alpha-intercalated cells

Question 29

What is the function of the principal cells?

Answer 29

They reabsorb Na+ and water and they secrete K+

Question 30

What hormones act on the Late distal tubule and collecting duct?

Answer 30

(1) aldosterone increases Na+ reabsorption and K+ secretion.

2) Antidiuretic hormone increases H2O permeability (without ADH no water would be reabsorbed by the principal cells

Question 31

What is the function of alpha-intercalated cells?

Answer 31

(1) secrete H+ (stimulated by aldosterone)

2) Reabsorb K+ (via an H+, K+ ATPase