Kidney Handling of NaCl and Water

Question 1

What is the daily filtration rate of plasma by the kidneys?

Answer 1

About 180 L of plasma daily.

Question 2

What are the major determinants of extracellular fluid (ECF) volume?

Answer 2

Sodium (Na(^+)) and chloride (Cl(^-)).

Question 3

What is the primary site of reclamation for NaCl and water in the nephron?

Answer 3

The proximal tubule.

Question 4

What percentage of filtered NaCl and water does the proximal tubule reabsorb?

Answer 4

About 60–70%.

Question 5

Which substances are primarily reabsorbed in the early proximal tubule?

Answer 5

Na(^+), glucose, amino acids, lactate, HCO(_3^-).

Question 6

What is the main mechanism of Na(^+) transport across the apical membrane?

Answer 6

Passive and active transport mechanisms.

Question 7

What is the role of Na/K–ATPase in Na(^+) transport?

Answer 7

Maintains the Na(^+) concentration gradient.

Question 8

How does Na(^+) enter the proximal tubule cells actively?

Answer 8

Through cotransport with solutes and Na/H exchanger.

Question 9

What substance is primarily secreted during the Na/H exchanger process?

Answer 9

H(^+).

Question 10

What happens to HCO(_3^-) during Na(^+) reabsorption?

Answer 10

It is generated and reabsorbed.

Question 11

What is the significance of the Na/H exchanger in the proximal tubule?

Answer 11

Responsible for most H(^+) secretion and Na(^+) reabsorption.

Question 12

What percentage of filtered Na(^+) is reabsorbed by the proximal tubule?

Answer 12

15,120–17,640 mEq (60–70%).

Question 13

What is the function of the Na/Cl cotransporter in the late proximal tubule?

Answer 13

Facilitates Cl(^-) entry coupled with Na(^+).

Question 14

What mechanism is primarily responsible for passive Cl(^-) reabsorption?

Answer 14

Paracellular pathway.

Question 15

What is the osmolality of the fluid in the thin descending limb of Henle’s loop?

Answer 15

Isosmotic (about 300 mOsm/kg H(_2)O) to plasma.

Question 16

What is the main characteristic of the thin ascending limb of Henle’s loop?

Answer 16

Impermeable to water, moderately permeable to urea.

Question 17

What is the primary transporter in the thick ascending limb of Henle’s loop?

Answer 17

Na/K/2Cl cotransporter.

Question 18

What is the osmolality of tubular fluid at the end of the thick ascending limb?

Answer 18

About 150 mOsm/kg H(_2)O.

Question 19

How does the thick ascending limb of Henle’s loop contribute to urine dilution?

Answer 19

By reabsorbing NaCl without reabsorbing water.

Question 20

What happens to K(^+) in the thick ascending limb of Henle’s loop?

Answer 20

It diffuses back into the tubular lumen via ROMK channels.

Question 21

What is the role of the Ca(^{2+})-sensing receptor (CaSR) in the thick ascending limb?

Answer 21

Regulates Na/K/2Cl cotransporter activity based on Ca(^{2+}) levels.

Question 22

What is the approximate reabsorption percentage of NaCl in the distal convoluted tubule?

Answer 22

About 5–10%.

Question 23

Fill in the blank: The distal convoluted tubule is divided into an early (D1) and _______.

Answer 23

late (D2) portion.

Question 24

True or False: The thick ascending limb of Henle’s loop is highly permeable to water.

Answer 24

False.

Question 25

What effect does blocking ROMK channels have on NaCl transport?

Answer 25

Decreases NaCl transport substantially.

Question 26

What segment of the nephron is beyond the macula densa?

Answer 26

Distal convoluted tubule (DCT) ## Footnote The DCT is a crucial part of kidney function involved in electrolyte balance.

Question 27

How is the distal convoluted tubule divided?

Answer 27

Into early (D1) and late (D2) portions ## Footnote This division helps in understanding the specific functions and transport mechanisms in each part.

Question 28

What percentage of NaCl is reabsorbed by the DCT and CNT?

Answer 28

Approximately 5–10% ## Footnote This reflects the kidney's ability to fine-tune electrolyte reabsorption.

Question 29

What transporter is found on the luminal side of the D1 portion of the DCT?

Answer 29

Na/Cl cotransporter (NCC) ## Footnote NCC plays a critical role in sodium and chloride reabsorption.

Question 30

What type of diuretics inhibit the Na/Cl cotransporter?

Answer 30

Thiazide diuretics ## Footnote Hydrochlorothiazide is a common example used in clinical settings.

Question 31

What is the stoichiometry of Na+ reabsorption mediated by NCC?

Answer 31

1Na+:1Cl- ## Footnote This electroneutral mechanism is essential for maintaining ionic balance in the nephron.

Question 32

What cotransporter promotes K+ secretion in the DCT?

Answer 32

Luminal K/Cl cotransporter ## Footnote The K/Cl cotransporter is vital for potassium homeostasis.

Question 33

True or False: Na+ delivery to the distal convoluted tubule is not necessary for K+ secretion.

Answer 33

False ## Footnote Na+ delivery is essential for the function of the K/Cl cotransporter and subsequent K+ secretion.