16 - Physiology of the Renal System II: Glomerular Filtration

Vocabulary flashcards covering key concepts from the lecture notes on glomerular filtration, nephron structure, and markers for kidney function.

Nephron

The functional unit of the kidney; comprises the glomerulus and renal tubules (proximal tubule, loop of Henle, distal tubule, collecting duct).

Glomerulus

Capillary tuft where blood is filtered into Bowman's space.

Bowman’s capsule

The capsule surrounding the glomerulus that collects filtrate from the capillaries.

Bowman’s space

The space within Bowman's capsule where filtrate first accumulates after filtration.

Afferent arteriole

Blood vessel that delivers blood to the glomerulus and helps regulate filtration pressure.

Efferent arteriole

Blood vessel that drains blood from the glomerulus; constriction/dilation modulates glomerular pressure.

Proximal tubule

Renal tubule segment where the majority of filtrate reabsorption occurs.

Loop of Henle

U-shaped tubule that concentrates urine via countercurrent mechanism.

Distal tubule

Renal tubule segment after the Loop of Henle; site of fine-tuning reabsorption and secretion.

Collecting duct

Final tubular segment where filtrate is collected and urine concentration is adjusted.

Filtration barrier

Three-layer barrier separating blood from Bowman's space: endothelium, basement membrane, and podocytes.

Endothelial fenestrations

Pores in glomerular capillary endothelium that permit filtration of water and small solutes.

Glomerular basement membrane

Negatively charged protein matrix forming part of the filtration barrier.

Podocytes

Epithelial cells with foot processes forming part of the filtration barrier.

Filtration slits

Gaps between podocyte foot processes through which filtrate passes.

Oncotic pressure

Osmotic pressure due to plasma proteins opposing filtration within capillaries.

Osmotic pressure

Pressure arising from solutes; in the glomerulus, largely from plasma proteins (oncotic).

Hydrostatic pressure

Fluid pressure inside glomerular capillaries driving filtration outward toward Bowman's space.

GFR (Glomerular Filtration Rate)

Volume of filtrate formed per minute by both kidneys; ~120 mL/min (≈180 L/day).

Filtration fraction

Proportion of renal plasma flow that becomes filtrate; typically about 0.2.

Renal blood flow

Total arterial blood flow to both kidneys (~1.1 L/min).

Renal plasma flow

The plasma component of renal blood flow; approximately 600 mL/min.

Peritubular capillaries

Capillary network surrounding the tubules after efferent arterioles; high oncotic pressure, low hydrostatic pressure.

Bulk flow

Movement of solvent (water) with pressure difference; carries dissolved solutes during filtration.

Diffusion

Movement of solutes down their concentration gradient; limited by distance and barrier complexity in the glomerulus.

Molecular size selectivity

Filtration barrier favors smaller molecules; typically passes molecules up to ~10 kDa; larger proteins are restricted.

Proteinuria

Presence of proteins in urine, indicating glomerular barrier dysfunction.

Nephrotic syndrome

Clinical condition with heavy proteinuria, hypoalbuminemia, edema, and often hyperlipidemia due to glomerular disease.

Congenital nephrotic syndrome

Rare genetic disorder (nephrin or podocin mutations) causing increased glomerular permeability to proteins.

Nephrin

Slit diaphragm protein in podocytes; mutations contribute to congenital nephrotic syndrome.

Podocin

Podocyte slit diaphragm protein; mutations contribute to congenital nephrotic syndrome.

Creatinine

Endogenous, constant-rate marker used to estimate GFR; freely filtered with minimal secretion or reabsorption.

Inulin

Exogenous filtration marker freely filtered and neither secreted nor reabsorbed; gold standard for measuring GFR.

Cockcroft-Gault formula

Empirical equation to estimate GFR using age, weight, and sex (used to derive eGFR).

eGFR

Estimated GFR calculated from serum creatinine and demographic factors; used clinically to assess kidney function.

Age-related GFR decline

GFR decreases with age due to nephron loss; creatinine production and serum levels are influenced by age.