18 - Renal Tubular Reabsorption – Vocabulary Flashcards

Vocabulary flashcards covering key terms from the lecture notes on renal physiology, focusing on tubular reabsorption, solute transport, and diuretics across the nephron.

Nephron

The kidney’s fundamental functional unit; consists of the glomerulus and a tubular system (PCT, loop of Henle, DCT, collecting duct).

Glomerulus

Capillary tuft where plasma filtration begins.

Bowman’s space

Cavity surrounding the glomerulus that collects filtrate before it enters the tubules.

Afferent arteriole

Arteriole delivering blood to the glomerulus.

Efferent arteriole

Arteriole carrying filtered blood away from the glomerulus.

Proximal tubule

Renal tubule segment responsible for bulk reabsorption of water and solutes; major site of proximal reabsorption.

Proximal convoluted tubule (PCT)

First 60% of the proximal tubule in the cortex; contains a dense brush border to increase absorption surface.

Proximal straight tubule

The remaining portion of the proximal tubule after the convoluted segment.

Brush border

Microvilli on the apical surface of PCT cells that increase absorptive surface area.

AQP1

Aquaporin-1 water channel in the proximal tubule and descending limb; mediates transcellular water movement.

Paracellular transport

Movement of substances between cells via tight junctions.

Transcellular transport

Movement of substances through cells via channels and transporters.

Na+/K+-ATPase

Basolateral pump maintaining Na+ gradient to drive apical reabsorption of solutes.

Na+ gradient

Electrochemical gradient that drives Na+-coupled transport of solutes in the proximal tubule.

SGLT2

Low-affinity/high-capacity Na+-glucose cotransporter; reabsorbs the majority of filtered glucose in the proximal tubule.

SGLT1

High-affinity/low-capacity Na+-glucose cotransporter; reabsorbs remaining glucose in the proximal tubule.

GLUT2

Basolateral glucose transporter that moves glucose from cells to the interstitial space.

GLUT1

Basolateral glucose transporter contributing to glucose efflux from tubular cells.

Tm (tubular maximum) for glucose

Maximal rate of glucose reabsorption by SGLTs (about 380 mg/min or 2.1 mmol/min).

Urea

Filtered solute; concentration rises along the proximal tubule as water is reabsorbed.

HCO3-

Bicarbonate; reabsorbed in the proximal tubule via Na+/H+ exchange and carbonic anhydrase–driven reactions.

Na+/H+ exchanger

Apical transporter that reabsorbs Na+ in exchange for H+, aiding HCO3- reabsorption.

Carbonic anhydrase

Enzyme catalyzing CO2 + H2O ⇌ HCO3- + H+; accelerates proximal bicarbonate handling.

Acetazolamide

Carbonic anhydrase inhibitor; proximal tubule diuretic; urine becomes alkaline and metabolic acidosis may occur.

OAT

Organic anion transporter on the basolateral membrane enabling secretion of organic anions (e.g., PAH, penicillin, furosemide).

MRP

Multidrug resistance-associated protein on the luminal membrane helping organic anion secretion.

PAH

Para-aminohippuric acid; actively secreted by the proximal tubule; used to estimate renal plasma flow.

Loop of Henle

Renal tubule with descending limb (water reabsorption) and thick ascending limb (solute transport) to create medullary hyperosmolarity.

NKCC2

Na+/K+/2Cl- cotransporter in the thick ascending limb; inhibited by furosemide; important for medullary osmotic gradient.

Furosemide

Loop diuretic that blocks NKCC2; causes significant natriuresis and diuresis; potential metabolic side effects.

Distal tubule

Site of Na+/Cl- cotransport; target of thiazide diuretics.

Thiazide

Block Na+/Cl- cotransport in the distal tubule; mild diuretic; used for hypertension and with loop diuretics.

Aldosterone

Mineralocorticoid that increases Na+ reabsorption in collecting ducts; may influence water handling via AQP2 according to notes.

ADH (vasopressin)

Antidiuretic hormone; increases the number of aquaporin-2 water channels in collecting ducts to promote water reabsorption.

AQP2

Vasopressin-regulated water channel in collecting ducts; insertion increases water reabsorption.

Medullary interstitial osmolarity

High osmolarity in the medullary interstitium; essential for driving water reabsorption in the loop and collecting ducts.

Descending limb

Part of the loop of Henle permeable to water; filtrate concentrates as water exits.

Thick ascending limb (TAL)

Segment that pumps Na+, K+, and Cl- out of filtrate via NKCC2 and is water-impermeable, helping establish medullary gradient.

UT-A1/UT-A2

Urea transporters in the nephron that facilitate urea movement, contributing to the medullary osmotic gradient (ADH increases UT-A1 expression).

Urea cycling

Urea is reabsorbed and secreted in a countercurrent arrangement to maintain medullary osmolality and promote water reabsorption.

Countercurrent multiplication

Process by which a horizontal osmotic gradient is generated in the medulla to drive water reabsorption.