Renal Physiology and Acid-Base Balance

Vocabulary flashcards covering key concepts of renal blood flow regulation, tubular transport mechanisms, clearance calculations, and renal acid-base physiology based on the lecture transcript.

Macula Densa

Specialized cells in the distal tubule that monitor renal blood flow and detect concentrations of sodium ($\text{Na}^+$) and chloride ($\text{Cl}^-$) to regulate glomerular filtration rate.

Tubuloglomerular Feedback

An intrinsic autoregulatory mechanism where macula densa cells sense tubular flow and solute concentration, emitting signals to adjust arteriolar resistance and renin secretion.

Renin

An enzyme secreted by juxtaglomerular (granular) cells in response to low glomerular pressure that converts angiotensinogen into angiotensin I.

Angiotensin II

A potent vasoactive peptide that increases efferent arteriolar resistance and stimulates tubular sodium and water reabsorption.

SGLT2

A low-affinity, high-capacity sodium-glucose cotransporter located in the proximal tubule that reabsorbs the majority of filtered glucose.

SGLT1

A high-affinity sodium-glucose cotransporter that reabsorbs the remaining filtered glucose in the tubule and increases its transport capacity when SGLT2 is inhibited.

Glucose Transport Maximum ($T_m$)

The maximum tubular reabsorption capacity for glucose, which averages $375\,\text{mg/min}$ compared to a normal filtered load of $125\,\text{mg/min}$.

Renal Clearance

The volume of plasma completely cleared of a substance by the kidneys per unit of time, calculated using the formula $\text{Clearance} = \frac{U_x \times V}{P_x}$.

Inulin

An exogenous substance that is freely filtered at the glomerulus but neither reabsorbed nor secreted, serving as the gold standard indicator for measuring glomerular filtration rate ($\text{GFR}$).

Para-aminohippuric Acid (PAH)

An exogenous compound cleared almost entirely in a single pass through the renal circulation, used as an indicator to measure effective renal plasma flow ($\text{RPF}$).

Creatinine

An endogenous breakdown product produced at a constant rate ($1.8\,\text{g/day}$) whose plasma concentration doubles when glomerular filtration rate is reduced by half.

Glomerulotubular Balance

The intrinsic ability of the proximal tubules to increase their reabsorption rate in response to an increased filtered load, maintaining reabsorption at approximately $65\%$ of glomerular filtration.

NKCC2

The $\text{Na}^+\text{-K}^+\text{-2Cl}^-$ cotransporter in the thick ascending limb of Henle's loop that generates the medullary osmotic gradient and is inhibited by loop diuretics like furosemide.

NHE3

A $\text{Na}^+/\text{H}^+$ antiporter located in the proximal tubule and thick ascending limb that reabsorbs sodium while secreting hydrogen ions ($\text{H}^+$) to enable bicarbonate recapture.

Aldosterone

A steroid hormone that acts on distal tubule and collecting duct cells to increase $\text{NaCl}$ and water reabsorption while enhancing $\text{K}^+$ and $\text{H}^+$ secretion.

Antidiuretic Hormone (ADH)

A hormone acting on collecting duct principal cells via $V_2$ receptors to insert aquaporins, increasing water permeability and urine concentration.

Carbonic Anhydrase

An essential enzyme that catalyzes the interconversion of carbon dioxide ($\text{CO}_2$) and water ($\text{H}_2\text{O}$) into carbonic acid ($\text{H}_2\text{CO}_3$), supporting renal acid-base balance and bicarbonate reabsorption.

Pendrin

An apical anion exchanger in type B intercalated cells that secretes bicarbonate ($\text{HCO}_3^-$) into the tubular lumen in exchange for chloride ($\text{Cl}^-$) during alkalosis.

Ammonia Buffering System

A renal acid-base mechanism where proximal tubule cells deaminate glutamine into two $\text{NH}_4^+$ ions (excreted in urine) and two new $\text{HCO}_3^-$ ions (returned to the blood).