CVD WK5 : Reabsoprtion

What is the function of the Na⁺/K⁺ ATPase on the basolateral membrane?

Pumps Na⁺ out of the cell into the blood, creating a gradient that drives reabsorption

What percentage of water is reabsorbed by the kidney?

~99% (180 L filtered, 1.8 L excreted)

What percentage of sodium is reabsorbed by the kidney?

~99.5%

What percentage of glucose is reabsorbed by the kidney?

100% (no glucose in urine normally)

What percentage of urea is reabsorbed by the kidney?

~44% (waste product, mostly excreted)

Where does the majority of reabsorption occur?

Proximal convoluted tubule (60-70% of water and Na⁺)

What is the main function of the proximal tubule?

Majority of reabsorption (water, Na⁺, glucose, amino acids)

Which transporter reabsorbs glucose in the proximal tubule?

SGLT (Sodium-Glucose Linked Transporter)

What is the function of the descending limb of the Loop of Henle?

Permeable to water - water leaves, concentrating the filtrate

What is the function of the ascending limb of the Loop of Henle?

Impermeable to water, permeable to solutes - salt leaves, diluting the filtrate

What is the function of the Loop of Henle?

Creates a concentration gradient in the medulla (countercurrent multiplier system)

What transporter in the thick ascending limb reabsorbs Na⁺, K⁺, and Cl⁻?

Na⁺/K⁺/2Cl⁻ co-transporter (NKCC2)

What does NKCC2 reabsorb?

1 Na⁺, 1 K⁺, and 2 Cl⁻

Which diuretics block the NKCC2 transporter?

Loop diuretics (e.g., furosemide)

What transporter in the distal convoluted tubule reabsorbs Na⁺ and Cl⁻?

Na⁺/Cl⁻ co-transporter (NCC)

Which diuretics block the NCC transporter?

Thiazide diuretics (e.g., bendroflumethiazide, hydrochlorothiazide)

What does aldosterone do in the distal tubule and collecting duct?

Increases Na⁺ reabsorption and K⁺ excretion

What does ADH (vasopressin) do in the collecting duct?

Increases aquaporins (water channels) → increases water reabsorption → concentrated urine

Where does final urine concentration occur?

Collecting duct

What is the effect of ADH on urine?

Concentrated urine (less water, more concentrated solutes)

What is the effect of no ADH on urine?

Dilute urine (diabetes insipidus)

What are aquaporins?

Water channels in the collecting duct that allow water to be reabsorbed

What is the countercurrent multiplier system?

The Loop of Henle creates a concentration gradient in the medulla by countercurrent flow

What is the site of action of loop diuretics?

Thick ascending limb (NKCC2 transporter)

What is the site of action of thiazide diuretics?

Distal convoluted tubule (NCC transporter)

What is the effect of aldosterone on Na⁺ reabsorption?

Increases Na⁺ reabsorption

What is the effect of aldosterone on K⁺ excretion?

Increases K⁺ excretion

What is the effect of ADH on aquaporins?

Increases the number of aquaporins in the collecting duct

What is the difference between the descending and ascending limbs of the Loop of Henle?

Descending = permeable to water, impermeable to solutes. Ascending = impermeable to water, permeable to solutes.

What percentage of Na⁺ is reabsorbed in the proximal tubule?

60-70%

What percentage of water is reabsorbed in the proximal tubule?

60-70%

What is the role of the medullary concentration gradient?

Allows the kidney to produce concentrated urine