3. 3 rd layer Podocyte cells = physical blockage that prevent large molecules from entering 1. Unless podocyte is infected or physically damaged, large molecules like RBC cannot squeeze through 4. Mesangial cells lie between the glomerular capillaries contract to alter blood flow. 1. Mesangial cells have cytoplasmic bundles of actin-like filaments that enable them to contract and alter blood flow through capillaries. 9. Driving forces of filtration 1. Net filtration = hydrostatic pressure – fluid pressure – osmotic pressure = 10 mm Hg 1. Main driving force: Hydrostatic pressure (blood pressure) 1. Blood pressure provides the hydrostatic pressure that drives glomerular filtration 2. The more liquid pushed into glomerulus balloon, the > the hydrostatic pressure 1. 20% of cardio output enters kidneys. 2. The high rate of blood flow through the kidneys is critical to renal function.
3. Pushes the liquid out of the glomerulus into lumen of bowman’s capsule to be filtered ~55 mm Hg 2. Fluid pressure created by fluid in bowman’s capsule; against filtration 1. Unlike interstitial fluid, bowman’s capsule is an enclosed space. The presence of fluid in the capsule creates hydrostatic pressure that opposes fluid movement into the capsule 1. Hydrostatic pressure acting in opposite direction ~ 15 mm Hg 3. Osmotic pressure – sieve prevents protein from entering blood; against filtration 1. Proteins are too large to be filtered. Water seeks to dilute the solute, or proteins, in this case ~ 30 mm Hg 1. Most of the fluid entering bowman’s capsule is isosmotic. 2. Heart edema causes fluid to accumulate around the pericardial membrane, decreasing blood pressure 1. B/c hydrostatic pressure is intertwined with BP, the liquid into the kidneys can’t be pushed in with enough force 1. Heart failure patients must be on temporary dialysis: CVD affects renal system. 3. Glomerular Filtration Rate = volume of plasma water filtered per time = 180L/day or 125 mL/min 1. Clinically used to assay kidney function 1. Compare clearance of X to GFR to determine renal threshold 1. RT = plasma concentration at which a substance first appears in urine. 4. Filtration Fraction = actual amount of particles filtered in per time 1. F(x) = GFR x plasma [x] 1. Volume is irrelevant; only the particles inside the volume are relevant 2. Renal plasma flow – amount of particle per volume 1. Blood flowing in from renal artery to afferent arteriole = 600 mL/min 2. 125/600 = 20% of blood from cardio output enter renal artery 1. 20% of the blood that enters is filtered into the nephron tubes. 1. >19% of filtered fluid is reabsorbed and < 1% is excreted. 2. The remaining 80% enter peritubular capillaries, renal vein 10. Autoregulation of GFR 11. Primary regulation of GFR: Afferent Arteriole 1. The effect of increased resistance on GFR depends on where resistance change takes place 1. Opposite GFR changes occur with decreased resistance in afferent or efferent arterioles.
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- Fall '19
- Physiology, Nephron