8131MED - Renal Physiology _Part 3 (glomerular filtration).pdf

Glomerular Filtration Dr. Nicole Flemming – [email protected] Learning Objectives 1. Describe the process of glomerular filtration and the physical forces that determine the rate at which it occurs (GFR). Body fluid compartments & composition High conc K+ plasma membranes separate plasma ha...

Glomerular Filtration Dr. Nicole Flemming – [email protected] Learning Objectives 1. Describe the process of glomerular filtration and the physical forces that determine the rate at which it occurs (GFR). Body fluid compartments & composition High conc K+ plasma membranes separate plasma has higher protein 50-60% WATER -ve protein content Fluid movement between compartments Movement of water, ions, solutes occurs are a result of diffusion, filtration, reabsorption not stagnant greater at arterial side Diffusion Concentration gradient hydrostatic pressure declines net movement of water from high to low concentration net movement Filtration Capillary hydrostatic pressure High pressure → low pressure through pores in membrane smalll force through cardiovascular system proteins left behind exit as hydrostatic pressure is greater than blood colloid pressure Reabsorption Osmotic pressure Solute concentration Blood colloid osmotic pressure / oncotic pressure water diffues to higher salt concentration greater osmotic pressure colloid osmotic pressure - displacement of water by proteins equal Glomerular filtration barrier Fluid filtered at the glomerulus must pass through 3 layers that make up the glomerular membrane. functional barrier with 3 layers plasma enters, fluid and small solutes are pushed out in Bowman's capsule A. Glomerular endothelial cell (capillary endothelium) line glomerulus blood cells maintained larger B. mesh of collagen solutes Glomerular regulate -vely charged proteins basement membrane low MW proteins escape then reabsorbed later essential to prevent loss of plasma proteins C. Podocyte Glomerular filtration pressures Three pressures contribute to glomerular filtration Glomerular hydrostatic pressure Blood colloid osmotic pressure Capsular hydrostatic pressure Glomerular hydrostatic pressure Blood colloid osmotic (oncotic) pressure Capsular hydrostatic pressure Glomerular filtration pressures Three pressures contribute to glomerular filtration Glomerular hydrostatic pressure maintain higher hydrostatic pressure efferent arteriole - smaller diameter as opposed to afferent Blood colloid osmotic pressure drive filtration Capsular hydrostatic pressure Glomerular hydrostatic pressure out of plasma heart pumping blood and contributing hydrostatic pressure Pressure at glomerular capillaries Greater than systemic circuit capillary pressure Pushes water and solutes out of plasma and into glomerular filtrate Glomerular hydrostatic pressure Glomerular filtration pressures Three pressures contribute to glomerular filtration Glomerular hydrostatic pressure Blood colloid osmotic pressure Capsular hydrostatic pressure Blood colloid osmotic (oncotic) pressure Blood colloid osmotic pressure Osmotic pressure resulting from unequal distribution of suspended proteins in plasma/filtrate Draws water from filtrate → plasma Opposes GHP oppose hydrostatic pressure water drawn in opposite direction small fenestrations large proteins remain Glomerular filtration pressures Three pressures contribute to glomerular filtration Glomerular hydrostatic pressure Blood colloid osmotic pressure Capsular hydrostatic pressure Capsular hydrostatic pressure Results from resistance to flow along the nephron (already contains fluid!) fluid pushed through Water and solutes from filtrate → plasma Opposes GHP opposite direction Capsular hydrostatic pressure Glomerular filtration pressures Glomerular hydrostatic pressure Blood colloid osmotic (oncotic) pressure Capsular hydrostatic pressure NET FILTRATION pressure = GHP – BCOP – CsHP = 55mmHg – 30mmHg – 15mmHg = ~10mmHg net filtration pressure Glomerular filtrate Fluid that is contained within the Bowman’s capsule becomes glomerular filtrate typically cell-free and protein-free same concentration of dissolved ions and small organic molecules as the plasma Glomerular hydrostatic pressure Protein-bound elements (e.g., calcium, fatty acids) Blood colloid osmotic (oncotic) pressure are not present, as they cannot be filtered through the glomerular filtration barrier calcium and fatty acids cannot filter Capsular hydrostatic pressure freely move through