Renal Physiology – Tubular Reabsorption & Secretion Vocabulary

Vocabulary flashcards covering key terms from the lecture on renal tubular reabsorption, secretion, and related transport mechanisms.

Filtrate

Fluid filtered into the glomerular capsule before it enters the renal tubule.

Tubular Fluid

Name given to filtrate once it enters the renal tubule; same substance, different location.

Tubular Reabsorption

Movement of substances from tubular fluid back into the blood, reclaiming useful solutes and water.

Tubular Secretion

Transfer of substances from blood, interstitial fluid, or tubule cells into tubular fluid for excretion.

Proximal Convoluted Tubule (PCT)

First tubule segment where most reabsorption of water, ions, glucose, and proteins occurs.

Collecting Duct (CD)

Final nephron segment that fine-tunes reabsorption and secretion, influenced by hormones like ADH.

Paracellular Pathway

Route of reabsorption in which solutes diffuse between adjacent tubule cells.

Transcellular Pathway

Route of reabsorption/secretion through the tubule cells, crossing both apical and basolateral membranes.

Tight Junction

Seal at the apical region joining tubule cells, limiting passive movement between them.

Apical Membrane

Tubule cell surface facing the lumen and tubular fluid.

Basolateral Membrane

Tubule cell surface facing interstitial fluid and blood.

Passive Diffusion

Movement of molecules down their concentration gradient without energy input.

Facilitated Diffusion

Passive transcellular transport via membrane channels or carriers (e.g., ion channels).

Aquaporin

Water channel protein enabling rapid water movement across cell membranes.

Primary Active Transport

ATP-powered pumping of substances against their concentration gradients (e.g., Na⁺/K⁺-ATPase).

Secondary Active Transport

Coupled transport using energy from one ion moving down its gradient to move another molecule against its gradient.

Symporter

Secondary transporter that moves two substances in the same direction across a membrane.

Antiporter

Secondary transporter that exchanges two substances in opposite directions.

Transport Maximum (Tm)

Upper limit of substance transport rate when all carriers are saturated, expressed in mg/min.

Obligatory Water Reabsorption

Water reabsorption (≈80%) that obligatorily follows solute movement, mainly in PCT and descending limb.

Facultative Water Reabsorption

Adjustable water reabsorption (≈20%) regulated by ADH in late DCT and collecting duct.

Antidiuretic Hormone (ADH)

Hormone that increases water permeability of late DCT and CD, promoting facultative water reabsorption.

Osmolarity

Concentration of solute particles per liter of solution; decreases when water is reabsorbed into blood.

Hyperkalemia

Dangerously elevated blood potassium levels; prevented partly by renal secretion of K⁺.

Creatinine

Metabolic waste fully secreted by kidneys; its urinary excretion is used to assess renal function.

Urea

Nitrogenous waste of protein metabolism; about half is reabsorbed and half excreted.

Hydrogen Ion Secretion

Active movement of H⁺ into tubular fluid, crucial for regulating blood pH.

Glomerular Filtration Rate (GFR)

Volume of filtrate produced per minute by both kidneys; previously discussed as 180 L/day estimate.

Secretion Equals Excretion

Principle that substances secreted into tubular fluid will be eliminated in urine unless reabsorbed.

Interstitial Fluid

Fluid surrounding tubule cells; intermediary between tubular fluid and blood during reabsorption/secretion.