Chapter 26, Lecture 6

Flashcards covering the transport processes and regulatory mechanisms in the nephron loop, distal convoluted tubule and collecting duct.

Which nephron segment performs most of the heavy-lifting for reabsorption?

The proximal convoluted tubule (PCT).

In the nephron loop, what percentage of chloride is reabsorbed?

About 35% of the filtered chloride.

What portion of filtered water is reabsorbed in the descending limb of the nephron loop?

Roughly 50% of the filtered water.

Why can water and solute reabsorption be regulated independently in the nephron loop?

Because the thick ascending limb is impermeable to water while it actively reabsorbs solutes.

What is the main functional advantage of uncoupling solute and water reabsorption in the nephron loop?

It allows independent control of body-fluid volume and osmolarity, enabling urine concentration during dehydration.

Name the key transporter found in the thick ascending limb.

The Na⁺-K⁺-2Cl⁻ symporter (also called the sodium-potassium-two-chloride symporter).

How many of each ion does the Na⁺-K⁺-2Cl⁻ symporter move from the tubular fluid into the cell?

1 Na⁺, 1 K⁺, and 2 Cl⁻ ions.

What happens to potassium that enters the thick ascending limb cell via the Na⁺-K⁺-2Cl⁻ symporter?

Most K⁺ leaks back into the tubular fluid through apical K⁺ channels, so it is not net-reabsorbed.

Which capillary network receives solutes reabsorbed from the nephron loop?

The vasa recta.

Why do cations such as Ca²⁺ and Mg²⁺ move paracellularly into the blood in the thick ascending limb?

A relative negative charge develops in the interstitium when K⁺ diffuses back into the lumen, drawing cations across tight junctions to balance charge.

Describe tubular fluid osmolarity as it descends the nephron loop.

It becomes progressively more concentrated (higher osmolarity) because water leaves while solutes stay.

Describe tubular fluid osmolarity as it ascends the thick ascending limb.

It becomes progressively more dilute (lower osmolarity) because NaCl is pumped out but water cannot follow.

What percentage of the remaining NaCl is reabsorbed in the early distal convoluted tubule (DCT)?

About 5% via Na⁺-Cl⁻ symporters.

Which ion’s reabsorption is the early DCT’s ‘claim to fame,’ and which hormone regulates it?

Calcium reabsorption, regulated by parathyroid hormone (PTH).

List the two major cell types found in the late DCT and collecting duct.

Principal cells and intercalated cells.

What is the function of principal cells?

They reabsorb Na⁺ and secrete K⁺; they have receptors for aldosterone and antidiuretic hormone (ADH).

Which hormones act on principal cells?

Aldosterone and antidiuretic hormone (ADH).

Why are principal cells considered the main source of urinary potassium?

Because they actively secrete K⁺ into the tubular fluid for excretion.

Differentiate Type A and Type B intercalated cells.

Type A: reabsorb HCO₃⁻ and secrete H⁺. Type B: secrete HCO₃⁻ and reabsorb H⁺.

What is the primary role of intercalated cells?

Regulation of blood and interstitial pH (acid–base balance).

Are symporters or antiporters involved in ion movement in the late DCT and collecting duct?

No; ion movement occurs via leakage channels and diffusion driven by the Na⁺/K⁺-ATPase gradient.

Which capillary network surrounds the late DCT?

The peritubular capillaries (not the vasa recta).

What physiological ‘wiggle room’ is provided by the late DCT and collecting duct?

Fine-tuning of the final 5–10% of solute and water reabsorption or secretion in response to the body’s moment-to-moment needs.