14.7 Basic Renal Processes for Sodium and Water

Aquaporins

Protein membrane channels through which water can diffuse

Countercurrent Multiplier System

Mechanism associated with loops of Henle that creates a region having high interstitial fluid osmolarity in renal medulla

Diuresis

Increased urine excretion

Hyperosmotic

Having total solute concentration greater than normal extracellular fluid

Hypoosmotic

Having total solute concentration less than that of normal extracellular fluid

Isoosmotic

Having the same total solute concentration as extracellular fluid

Na-K-2Cl Cotransporter (NKCC)

Mediated-transport protein that is involved in active transport of Na+, K+, and Cl- in the ascending limb of the loop of Henle

Obligatory Water Loss

Minimal amount of water required to excrete waste products

Osmotic Diuresis

Increase in urine flow resulting from increased solute excretion (e.g., glucose in uncontrolled diabetes mellitus)

Vasopressin (Antidiuretic Hormone)

Peptide hormone synthesized in hypothalamus and released from posterior pituitary gland; increases water permeability of kidneys’ collecting ducts and causes vasoconstriction

Water Diuresis

Increase in urine flow due to increased water output (usually due to decreased secretion or action of vasopressin)