L29 : Distal Tubule and Collecting Duct

Which segment of the distal nephron is the principal target of antidiuretic hormone (ADH) for water reabsorption?

The collecting duct

What cell types compose the last segment of the distal tubule and collecting duct?

Principal cells and two types of intercalated cells (α-intercalated and β-intercalated).

What are the main transport roles of principal cells in the distal nephron?

Reabsorb NaCl and water; secrete K+.

what does the initial segment of the distal tubule reabsorb?

• reabsorbs: Na+ , Cl-, and Ca2+

• impermeable to water

what is the target of thiazide diuretics in the distal tubule?

target the Na+/Cl- symporter

where does dilution of tubular fluid begin?

thick ascending limb and continues in the early segment of the distal tubule

function of principle cells in distal nephron

• reabsorb: NaCl and water

• secrete: K+

Which pump on the basolateral membrane powers Na+ reabsorption in the distal nephron?

Na+/K+-ATPase, which maintains a low intracellular Na+ and creates a driving force for Na+ entry via apical transporters.

Which apical transporter mediates Na+ entry in the early distal tubule and is the target of thiazide diuretics?

Na+-Cl− cotransporter (NCC) in the early distal tubule.

electrochemical gradient in distal tubule

Reabsorption of Na+ generates a negative luminal voltage and provides the driving force for paracellular reabsorption of Cl–

How does aldosterone influence Na+ and K+ handling in the distal nephron?

1. drives Na+/K+-ATPase pump

2. negative gradient created

3. drives chloride reabsorption

How does the sodium-potassium ATPase contribute to sodium reabsorption in the distal nephron through secondary active transport?

It establishes a sodium gradient by actively pumping sodium out of the tubular cells into the interstitial space.

What are the main actions of Type A (α) intercalated cells?

• Secrete H+

• reabsorb HCO3−

alpha intercalated cells are associated with…

acidosis

beta intercalated cells are associated with…

alkalosis

What segments of the nephron secrete

H+ to reduce acidosis?

1. alpha-intercalculated cell on the cortical collecting duct

2. proximal tubule (glutamine converted to ammonium)

what regulates the intercalcated cell transporters?

aldosterone

What are the main actions of Type B (β) intercalated cells?

• Secrete: HCO3−

• reabsorb: H+ and Cl−

What effect does aldosterone have on H+ secretion?

Aldosterone promotes H+ secretion via the α-intercalated cells (and increases K+ secretion).

what is the stimuli for aldosterone?

1. hyponatremia

2. hyperkalemia

function of aldosterone

control ECF volume by activating RAAS to promote Na+ reabsorption and increasing K+/H+ secretion

where is aldosterone released from?

adrenal cortex

what is a  a clinical condition in animals or humans that is due to a lack of ADH or lack of response to ADH?

nephrogenic diabetes insipidus (antagonist binding of receptors for ADH)

What might be the consequence to sodium, potassium, and hydrogen ion plasma concentration in case of a lower aldosterone secretion?

1. hyponatremia

2. hypokalemia

What hormone increases water reabsorption in the collecting duct?

Antidiuretic hormone (ADH, vasopressin).

What is the effect of atrial natriuretic peptide (ANP) on NaCl reabsorption in the distal nephron?

ANP decreases NaCl reabsorption in the distal tubule and collecting duct.

What effect does Angiotensin II have on the proximal tubule, thick ascending limb, and distal tubule?

Increases NaCl and water reabsorption and promotes H+ secretion.

What is the role of PTH in renal calcium and phosphate handling?

Increases calcium reabsorption and decreases phosphate reabsorption (in proximal tubule, thick ascending limb, and distal tubule).

What transporter mediates bicarbonate handling in β-intercalated cells (pendrin)?

Cl−/HCO3− antiporter (pendrin) on the apical membrane.

ADH

increases water reabsorption in collecting duct

PTH

increases calcium reabsorption and decreases phosphate reabsorption