Urinary System & Nephron Function

Vocabulary flashcards covering key structures, processes, and terms related to the urinary system and nephron function.

Osmotic Pressure

The force that regulates water and solute balance across membranes throughout the body.

Metabolic Wastes

By-products of cellular metabolism such as carbon dioxide and nitrogenous wastes that must be eliminated.

Urinary System

Organ system that maintains osmotic balance and removes metabolic wastes; includes kidneys, ureters, bladder, and urethra.

Kidney

Bean-shaped organ containing nephrons that filter blood and produce urine.

Nephron

The functional unit of the kidney (~1 million per kidney) that filters blood and forms urine.

Glomerulus

Specialized cluster of capillaries where blood filtration begins.

Bowman’s Capsule

Cup-shaped structure surrounding the glomerulus that collects filtrate.

Filtrate

Fluid entering the nephron; contains water, salts, glucose, amino acids, ions, urea, and other small molecules.

Reabsorption

Movement of substances from nephron tubule back into interstitial fluid and blood.

Renal Secretion

Active or passive transport of substances from blood into the nephron tubule for excretion.

Passive Transport

Movement of molecules down a concentration gradient without ATP (e.g., diffusion, facilitated diffusion).

Active Transport

Energy-requiring movement of substances against a concentration gradient (uses ATP).

Proximal Convoluted Tubule (PCT)

First nephron segment after Bowman’s capsule; site of major reabsorption of water, salts, glucose, amino acids, and bicarbonate; secretes H⁺ and NH₄⁺.

Loop of Henle

Nephron segment with descending and ascending limbs that establishes a salt gradient in the medulla.

Descending Limb

Portion of Loop of Henle rich in aquaporins; reabsorbs water into hypertonic interstitial fluid.

Aquaporins

Water channels that facilitate rapid water movement across cell membranes.

Ascending Limb

Segment of Loop of Henle lacking aquaporins; reabsorbs salt, first passively then actively, making filtrate dilute.

Interstitial Fluid (Kidney Medulla)

Fluid surrounding nephron tubules; becomes hypertonic due to salt reabsorption, driving water movement.

Hypertonic

Having a higher solute concentration relative to another solution, causing water to move toward it.

Distal Convoluted Tubule (DCT)

Nephron segment that fine-tunes pH and ion balance by secreting H⁺, K⁺, NH₄⁺ and reabsorbing salts, water, bicarbonate.

Collecting Duct

Final nephron pathway where filtrate becomes urine; water reabsorption is hormonally regulated to control urine concentration.

Urea

Nitrogenous waste produced by the liver from protein breakdown; partially reabsorbed and secreted in nephron.

Ureter

Tube that carries urine from each kidney to the bladder.

Bladder

Muscular sac that stores urine before elimination.

Urethra

Duct through which urine is expelled from the body.

Osmosis

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

pH Regulation (Kidney)

Adjustment of blood acidity via secretion or reabsorption of H⁺ and bicarbonate in nephron segments.

Nitrogenous Waste

Waste products containing nitrogen (e.g., urea) formed from amino acid and protein metabolism.