Concentration and Dilution of Urine

These flashcards cover the physiological mechanisms of urine concentration and dilution, including the roles of ADH, the Loop of Henle, and the vasa recta.

Minimum Urine Osmolarity

The lowest solute concentration the kidney can produce during overhydration, which is approximately $50\,mosm/L$.

Maximum Urine Osmolarity

The highest solute concentration the kidney can produce during dehydration, which is approximately $1200\,mosm/L$, or $4$ times the plasma concentration.

Antidiuretic Hormone (ADH)

Also known as Vasopressin, this hormone is secreted by the posterior pituitary to increase water permeability in the distal tubules and collecting ducts.

Dilute Urine Formation

Process occurring when water content in the body is high and ADH secretion is inhibited, preventing water reabsorption from renal tubules.

Countercurrent System

A system of 'U' shaped tubules in the kidney (loop of Henle and vasa recta) where fluid flows in opposite directions in two limbs.

Countercurrent Multiplier

The role of the Loop of Henle in creating the medullary osmotic gradient.

Countercurrent Exchanger

The role of the vasa recta in maintaining the medullary gradient without dissipating the hyperosmolarity.

Descending Limb of the Loop of Henle

The portion of the loop of Henle that is permeable to water but not to solutes, making the tubular fluid more concentrated as it descends.

Ascending Limb of the Loop of Henle

The portion of the loop of Henle that is impermeable to water but actively transports $Na^+$, $K^+$, and $Cl^-$ ions into the interstitium.

Single Effect

The small osmotic gradient created by the active transport of solutes out of the ascending limb of the loop of Henle.

Corticomedullary Osmotic Gradient

The osmotic gradient reaching up to $1200\,mOsm/L$ in the deep medulla, established by the countercurrent multiplier.

Vasa Recta Mechanism

Sluggish blood flow through these capillaries allows solutes to accumulate in the descending limb and return to the interstitium from the ascending limb, preventing gradient washout.

Urea Recycling

A process that contributes to the development and maintenance of the hyperosmotic renal medullary interstitium.

Aquaporins

Water channels added to the distal convoluted tubule and collecting ducts by ADH to facilitate water reabsorption into the blood.