Kidney Handling of NaCl and Water Flashcards
What is the daily filtration rate of plasma by the kidneys?
About 180 L of plasma daily.
What are the major determinants of extracellular fluid (ECF) volume?
Sodium (Na(^+)) and chloride (Cl(^-)).
What is the primary site of reclamation for NaCl and water in the nephron?
The proximal tubule.
What percentage of filtered NaCl and water does the proximal tubule reabsorb?
About 60–70%.
Which substances are primarily reabsorbed in the early proximal tubule?
Na(^+), glucose, amino acids, lactate, HCO(_3^-).
What is the main mechanism of Na(^+) transport across the apical membrane?
Passive and active transport mechanisms.
What is the role of Na/K–ATPase in Na(^+) transport?
Maintains the Na(^+) concentration gradient.
How does Na(^+) enter the proximal tubule cells actively?
Through cotransport with solutes and Na/H exchanger.
What substance is primarily secreted during the Na/H exchanger process?
H(^+).
What happens to HCO(_3^-) during Na(^+) reabsorption?
It is generated and reabsorbed.
What is the significance of the Na/H exchanger in the proximal tubule?
Responsible for most H(^+) secretion and Na(^+) reabsorption.
What percentage of filtered Na(^+) is reabsorbed by the proximal tubule?
15,120–17,640 mEq (60–70%).
What is the function of the Na/Cl cotransporter in the late proximal tubule?
Facilitates Cl(^-) entry coupled with Na(^+).
What mechanism is primarily responsible for passive Cl(^-) reabsorption?
Paracellular pathway.
What is the osmolality of the fluid in the thin descending limb of Henle’s loop?
Isosmotic (about 300 mOsm/kg H(_2)O) to plasma.
What is the main characteristic of the thin ascending limb of Henle’s loop?
Impermeable to water, moderately permeable to urea.
What is the primary transporter in the thick ascending limb of Henle’s loop?
Na/K/2Cl cotransporter.
What is the osmolality of tubular fluid at the end of the thick ascending limb?
About 150 mOsm/kg H(_2)O.
How does the thick ascending limb of Henle’s loop contribute to urine dilution?
By reabsorbing NaCl without reabsorbing water.
What happens to K(^+) in the thick ascending limb of Henle’s loop?
It diffuses back into the tubular lumen via ROMK channels.
What is the role of the Ca(^{2+})-sensing receptor (CaSR) in the thick ascending limb?
Regulates Na/K/2Cl cotransporter activity based on Ca(^{2+}) levels.
What is the approximate reabsorption percentage of NaCl in the distal convoluted tubule?
About 5–10%.
Fill in the blank: The distal convoluted tubule is divided into an early (D1) and _______.
late (D2) portion.
True or False: The thick ascending limb of Henle’s loop is highly permeable to water.
False.
What effect does blocking ROMK channels have on NaCl transport?
Decreases NaCl transport substantially.
What segment of the nephron is beyond the macula densa?
Distal convoluted tubule (DCT)
The DCT is a crucial part of kidney function involved in electrolyte balance.
How is the distal convoluted tubule divided?
Into early (D1) and late (D2) portions
This division helps in understanding the specific functions and transport mechanisms in each part.
What percentage of NaCl is reabsorbed by the DCT and CNT?
Approximately 5–10%
This reflects the kidney’s ability to fine-tune electrolyte reabsorption.
What transporter is found on the luminal side of the D1 portion of the DCT?
Na/Cl cotransporter (NCC)
NCC plays a critical role in sodium and chloride reabsorption.
What type of diuretics inhibit the Na/Cl cotransporter?
Thiazide diuretics
Hydrochlorothiazide is a common example used in clinical settings.
What is the stoichiometry of Na+ reabsorption mediated by NCC?
1Na+:1Cl-
This electroneutral mechanism is essential for maintaining ionic balance in the nephron.
What cotransporter promotes K+ secretion in the DCT?
Luminal K/Cl cotransporter
The K/Cl cotransporter is vital for potassium homeostasis.
True or False: Na+ delivery to the distal convoluted tubule is not necessary for K+ secretion.
False
Na+ delivery is essential for the function of the K/Cl cotransporter and subsequent K+ secretion.
