Renal Physiology: Glomerular Filtration and Water Excretion

Glomerulus

Specialized structure for blood filtration.

Afferent Arteriole

Larger diameter vessel supplying glomerulus.

Efferent Arteriole

Drains blood from the glomerulus.

Peritubular Capillaries

Arise from efferent arterioles, drain into venules.

Vasa Recta

Capillaries associated with the nephron loop.

Filtration Membrane

Barrier preventing large molecules from passing.

Net Filtration Pressure (NFP)

Pressure driving fluid from glomerulus to capsule.

HPgc

Glomerular hydrostatic pressure, 55 mm Hg.

OPgc

Osmotic pressure in glomerulus, 30 mm Hg.

HPcs

Capsular hydrostatic pressure, 15 mm Hg.

GFR

Glomerular filtration rate, volume filtered per time.

Plasma Creatinine

Used to estimate GFR in clinical settings.

Plasma Urea Clearance

Measurement of urea excretion efficiency.

Tubular Reabsorption

Returns 99% of filtrate back to blood.

Tubular Secretion

Moves substances from blood to filtrate.

Clearance

Volume of plasma cleared of a substance.

Filtration Fraction (FF)

Ratio of GFR to renal plasma flow.

Myogenic Mechanism

Intrinsic response regulating renal blood flow.

Juxtaglomerular Feedback

Regulates GFR through feedback mechanisms.

Sympathetic Mechanism

Extrinsic control affecting GFR and blood pressure.

Renin-Angiotensin Mechanism

Hormonal response maintaining blood pressure.

Urine Flow Rate (V)

Rate of urine production, measured in ml/min.

Glomerular Filtration Rate (GFR)

Rate of plasma filtered by kidneys per minute.

Plasma Creatinine Concentration

Creatinine level in plasma, measured in µM/l.

Urine Creatinine Concentration

Creatinine level in urine, measured in µM/l.

Urine Flow Rate

Volume of urine produced per minute, in ml/min.

Creatinine Clearance (CCr)

Volume of plasma cleared of creatinine per minute.

Cockcroft-Gault Equation

Formula to estimate creatinine clearance based on age, weight.

Modification of Diet in Renal Disease (MDRD)

Equation to estimate GFR using serum creatinine and age.

Plasma Urea Clearance

Measurement of urea excretion relative to plasma concentration.

Blood Urea Nitrogen (BUN)

Measure of urea in blood, influenced by GFR.

Renal Blood Flow Proportions

Distribution of blood flow in renal cortex and medulla.

Filtered Load

Amount of substance filtered by kidneys per minute.

Secretion

Process of substances being added to urine from blood.

PAH Clearance

Measurement of para-aminohippuric acid clearance from plasma.

Plasma Clearance

Volume of plasma cleared of a substance over time.

Plasma Clearance vs GFR

Comparison of clearance rates to assess kidney function.

Urine Concentration Ratio

Comparison of urine to plasma concentration for substances.

Serum Creatinine (SCr)

Creatinine level in serum, measured in mg/dL.

Age Factor in GFR

Age affects GFR calculations in Cockcroft-Gault equation.

Weight Factor in GFR

Weight is used in GFR calculations for accuracy.

Creatinine Excretion

Amount of creatinine excreted in urine per time.

Impact of GFR Decrease

Increased plasma creatinine indicates reduced GFR.

Juxtaglomerular Apparatus

Regulates renal function at nephron junction.

JG Cells

Granular smooth muscle cells; secrete renin.

Macula Densa Cells

Chemoreceptors monitoring filtrate osmolarity.

Filtrate Formation

Process of producing urine from blood.

Systemic Blood Pressure

Overall pressure in the circulatory system.

Intrinsic Mechanisms

Body's internal controls for renal function.

Myogenic Mechanism

Smooth muscle contraction in response to stretch.

Tubuloglomerular Feedback

Feedback mechanism regulating GFR via NaCl.

Renal Autoregulation

Maintains constant GFR despite blood pressure changes.

Afferent Arterioles

Blood vessels supplying blood to glomeruli.

Efferent Arterioles

Blood vessels draining blood from glomeruli.

Hypovolemic Shock

Severe drop in blood volume affecting organs.

Vasodilation

Widening of blood vessels to increase flow.

Vasoconstriction

Narrowing of blood vessels to reduce flow.

Glomerular Filtration Rate (GFR)

Rate of filtrate formation in kidneys.

Renin

Hormone regulating blood pressure and fluid balance.

Angiotensin II

Vasoconstrictor increasing blood pressure and volume.

Aldosterone

Hormone increasing sodium reabsorption in kidneys.

Neural Controls

Sympathetic nervous system response during stress.

Norepinephrine

Neurotransmitter causing vasoconstriction and increased BP.

Extrinsic Mechanisms

External factors influencing renal function and BP.

Na-K-ATPase

Enzyme regulating sodium and potassium balance.

ATP

Energy molecule; influences vascular responses.

CLEARANCE

Volume of plasma completely cleared of substances.

GFR

Glomerular filtration rate, measured in ml/min.

Creatinine

Muscle-produced substance used to estimate GFR.

Plasma Creatinine

Concentration of creatinine in plasma, mg/ml.

Urine Creatinine

Concentration of creatinine in urine, mg/ml.

Urine Flow Rate

Rate of urine production, measured in ml/min.

GFR Equation

GFR = (U x V) / P.

Filtered Load

Amount of substance filtered from plasma to urine.

Renal Blood Flow Proportions

Cortex: 93%, Outer medulla: 6.3%, Inner medulla: 0.7%.

PPAH

Para-aminohippuric acid, used to measure renal plasma flow.

RPF

Renal plasma flow, volume of plasma passing through kidneys.

Secretion

Process of substances moving from blood to urine.

ADH

Antidiuretic hormone regulating water retention.

Counter-current Multiplier

Mechanism concentrating urine in the kidney.

Vasa Recta

Blood vessels maintaining osmotic gradient in kidneys.

Hyperosmolality

Higher concentration of solutes in a solution.

Hypoosmolality

Lower concentration of solutes in a solution.

Juxtamedullary Nephrons

15% of nephrons, involved in urine concentration.

Cortical Nephrons

85% of nephrons, primarily located in cortex.

Antidiuresis

Conservation of water, reducing urine output.

Water Diuresis

Increased urine output due to excess water intake.

Plasma Osmolality

Concentration of solutes in plasma, affects ADH.

Nephron Loop

Structure involved in urine concentration processes.

Juxtamedullary Nephrons

Nephrons with long loops creating osmotic gradient.

Countercurrent Mechanism

Fluid flows oppositely in adjacent nephron segments.

Countercurrent Multiplier

Filtrate interaction in nephron loops enhancing concentration.

Countercurrent Exchanger

Blood flow in vasa recta maintaining osmotic balance.

Osmotic Gradient

Variation from 300 mOsm to 1200 mOsm.

Descending Limb

Permeable to water, concentrates filtrate osmolality.

Ascending Limb

Impermeable to water, reabsorbs Na+ and Cl-.

Filtrate Osmolality

Increases to ~1200 mOsm in descending limb.

Filtrate Dilution

Decreases to 100 mOsm in ascending limb.

Hyperosmotic Fluid

Interstitial fluid with higher solute concentration.

Active Transport

Energy-dependent process moving solutes against gradient.