Dilute and Concentrated Urine Formation

Vocabulary flashcards summarizing key renal physiology terms related to the formation of dilute and concentrated urine, ADH action, medullary gradients, and diuretics.

Antidiuretic hormone (ADH)

Pituitary hormone that increases water and urea permeability in the late distal convoluted tubule and collecting duct, promoting water reabsorption and concentrated urine.

Dilute urine

Urine produced when ADH levels are low or absent; characterized by low osmolarity and high volume.

Concentrated urine

Urine produced when ADH is present; characterized by high osmolarity and low volume.

Thick ascending limb

Segment of the nephron loop impermeable to water that actively transports Na⁺, K⁺, and Cl⁻ into the medullary interstitium.

Na⁺-K⁺-2Cl⁻ symporter

Membrane transporter in the thick ascending limb that pumps sodium, potassium, and chloride out of tubular fluid to establish the medullary gradient.

Medullary osmotic gradient

Progressive increase in solute concentration from the renal cortex toward the inner medulla that drives water movement in the nephron.

Juxtamedullary nephron

Nephron with long loops of Henle that extend deep into the medulla and are crucial for establishing the osmotic gradient.

Vasa recta

Hairpin-shaped capillaries surrounding the nephron loop that preserve the medullary osmotic gradient via counter-current exchange.

Interstitial fluid (renal medulla)

Fluid surrounding nephron segments in the kidney; its osmolarity is key to water reabsorption.

Descending limb

Thin segment of the nephron loop permeable to water but not to salts; loses water to equilibrate with the hyperosmotic medulla.

Ascending limb

Portion of the nephron loop that pumps salts into the medulla but is impermeable to water, diluting the tubular fluid.

Collecting duct

Final tubular segment that adjusts urine volume and osmolarity through ADH-regulated water and urea movement.

Late distal convoluted tubule

Nephron portion that, with the collecting duct, responds to ADH and fine-tunes water and ion reabsorption.

Principal cells

Cells in the late distal convoluted tubule and collecting duct that contain Na⁺/K⁺ pumps and respond to ADH.

Na⁺/K⁺ ATPase

Basolateral membrane pump in principal cells that actively transports sodium out and potassium in, aiding osmotic gradients.

Aquaporins

Water channel proteins inserted into principal cells by ADH to increase water permeability.

Urea transporters

ADH-regulated proteins in the collecting duct that facilitate urea movement into and out of tubular fluid.

Urea recycling

Process in which urea exits the collecting duct, enters the medullary interstitium, and re-enters thin nephron limbs, augmenting the osmotic gradient.

Osmolarity

Measure of solute concentration (osmoles per liter); determines water movement across nephron segments.

Hypo-osmotic

Having lower osmolarity than a reference fluid; describes tubular fluid leaving the ascending limb in dilute urine formation.

Hyperosmotic

Having higher osmolarity than a reference fluid; describes final urine when concentrated.

Osmosis

Passive movement of water across a semipermeable membrane from low solute to high solute concentration.

Papillary duct

Terminal portion of the collecting system that delivers urine into the minor calyx.

Diuresis

Increased urine flow rate.

Diuretic

Substance or drug that promotes diuresis by reducing water reabsorption in the nephron.

Caffeine

Common diuretic that inhibits sodium reabsorption in the distal convoluted tubule and collecting duct.

Furosemide (Lasix)

Loop diuretic that blocks the Na⁺-K⁺-2Cl⁻ symporter in the thick ascending limb, reducing the medullary gradient.

Alcohol

Diuretic that inhibits ADH release, decreasing water reabsorption in the collecting duct.

Edema

Accumulation of excess fluid in interstitial spaces, often treated with diuretics.

Blood plasma osmolarity

Concentration of solutes in plasma; rise triggers ADH release, fall suppresses it.