Renal Physiology Master Exam Guide Flashcards

Comprehensive vocabulary flashcards covering renal physiology mechanisms, nephron segments, diuretics, acid-base balance, and electrolyte homeostasis based on the Renal Physiology Master Exam Guide.

Filtration

The movement of substances from glomerular capillary plasma into the Bowman space, where water and small solutes pass while cells and most albumin are retained.

Reabsorption

The movement of substances from the tubular lumen back into the blood, such as glucose, Na+, water, and $HCO_3^-$.

Secretion

The movement of ions or waste, such as $H^+$, $K^+$, and many drugs, from the blood or tubular cells into the lumen.

Excretion Equation

$$\text{Excretion} = \text{filtration} - \text{reabsorption} + \text{secretion}$$

Erythropoietin (EPO)

Produced by interstitial fibroblast-like cells that sense hypoxia; its deficiency in CKD leads to normocytic anemia.

1-alpha-hydroxylase

An enzyme located in the kidney's proximal tubule that converts vitamin D to its active form, calcitriol ($1,25\text{-dihydroxyvitamin D}$).

Proximal Tubule

Site of bulk, largely iso-osmotic reabsorption of approximately $65\text{-}70\%$ of filtered $Na^+$ and water, utilizing transporters like NHE3 and SGLT.

Thick Ascending Limb (TAL)

The water-impermeable segment that builds the medullary gradient and dilutes tubular fluid via the NKCC2 transporter.

Collecting Duct

The nephron segment responsible for the final regulated control of $Na^+$, $K^+$, $H^+$, and water using ENaC, ROMK, and AQP2.

Basolateral $Na^+/K^+$-ATPase

A pump that exports $3\,Na^+$ and imports $2\,K^+$ per ATP, creating the low intracellular $Na^+$ gradient that drives most apical $Na^+$-coupled transport.

Single-nephron GFR Equation

$$\text{GFR} = K_f \times [ (P_{\text{GC}} - P_{\text{BS}}) - (\pi_{\text{GC}} - \pi_{\text{BS}}) ]$$

$K_f$ (Filtration Coefficient)

A variable in the GFR equation reflecting the filtration surface area and hydraulic permeability.

Tubuloglomerular Feedback

A mechanism where high NaCl at the macula densa triggers ATP/adenosine signaling to cause afferent constriction and reduce GFR.

Inulin

A substance that is freely filtered but not reabsorbed, secreted, or metabolized; used as the gold standard for estimating GFR.

Creatinine Clearance Limitation

It modestly overestimates true GFR because creatinine is slightly secreted in addition to being filtered.

Effective Renal Plasma Flow (ERPF)

An estimate of renal plasma flow measured using PAH clearance, which is nearly fully extracted in one pass at low plasma levels.

Filtration Fraction

$$\text{Filtration Fraction} = \frac{\text{GFR}}{\text{RPF}}$$

Renal Blood Flow (RBF) Formula

$$\text{RBF} = \frac{\text{RPF}}{1 - \text{hematocrit}}$$

Acetazolamide

A diuretic that inhibits proximal carbonic anhydrase, leading to bicarbonaturia, alkaline urine, and metabolic acidosis.

SGLT2 Inhibitors

Drugs like empagliflozin that block proximal glucose and $Na^+$ uptake, restore tubuloglomerular feedback, and cause mild natriuresis.

Loop Diuretics

Drugs such as furosemide that block NKCC2 in the TAL, weakening the medullary gradient and causing hypokalemic metabolic alkalosis.

Thiazide Diuretics

Drugs that block the NCC transporter in the Distal Convoluted Tubule, often causing hyponatremia and decreased urinary $Ca^{2+}$ excretion.

Amiloride

A potassium-sparing diuretic that directly blocks ENaC in the collecting duct; used to treat Liddle syndrome.

RAAS Pathway Activation

Stimulated by low afferent perfusion pressure, beta-1 sympathetic stimulation, or low macula densa NaCl.

Aldosterone Actions

Binds mineralocorticoid receptors in principal cells to increase ENaC, $Na^+/K^+$-ATPase, and $K^+$ channel activity; also promotes $H^+$ secretion in alpha-intercalated cells.

Glomerulotubular Balance

The principle that the proximal tubule reabsorbs a relatively constant fraction of the filtered load, protecting distal segments from extreme load changes.

Countercurrent Multiplication

A process involving opposing flows and repeated TAL salt transport that creates the corticomedullary gradient.

Vasa Recta Countercurrent Exchange

A slow hairpin blood flow system with passive exchange that preserves the medullary gradient.

ADH (Antidiuretic Hormone) Mechanism

Binds basolateral V2 receptors, activates cAMP/PKA signaling, and inserts Aquaporin-2 into the apical membrane of collecting duct principal cells.

Central Diabetes Insipidus

A condition caused by insufficient ADH secretion resulting in polyuria and low urine osmolality, which improves with desmopressin.

Nephrogenic Diabetes Insipidus

A condition of renal resistance to ADH resulting in polyuria that does not respond to desmopressin.

SIADH (Syndrome of Inappropriate Antidiuretic Hormone)

Inappropriately high ADH effect causing euvolemic hypotonic hyponatremia and concentrated urine.

Internal $K^+$ Balance Factors

Redistribution of potassium into cells mediated by insulin, beta-2 agonists (albuterol), and alkalemia.

Principal-cell $K^+$ Secretion Factors

Increased by high aldosterone, high distal $Na^+$ delivery, high tubular flow, and high plasma $K^+$.

PTH (Parathyroid Hormone) Actions

Increases $Ca^{2+}$ reabsorption in the DCT, decreases Na-phosphate cotransport in the proximal tubule, and stimulates 1-alpha-hydroxylase.

CKD Mineral-Bone Pathway

Falling GFR causes phosphate retention, increased FGF23, reduced calcitriol, and hypocalcemia, leading to secondary hyperparathyroidism.

Anion Gap Equation

$\text{Anion Gap} = [Na^+] - ( [Cl^-] + [HCO_3^-] )$; normal range is roughly $8\text{-}12\,mEq/L$.

Winter Formula

$\text{Expected } PCO_2 = 1.5 \times [HCO_3^-] + 8 \pm 2$; used to check respiratory compensation in metabolic acidosis.

Liddle Syndrome

An autosomal dominant gain-of-function mutation of ENaC causing hypertension, volume expansion, and hypokalemia with low renin and aldosterone.

Fanconi Syndrome

Generalized proximal transport failure leading to glucosuria, phosphaturia, aminoaciduria, and proximal renal tubular acidosis.