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3-25 - The Nephron: blood processing unit functions more in...

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1 The Nephron: blood processing unit 1. Glomerulus: tuft of capillaries associated with renal tubule 2. Glomerular (Bowman’s) Capsule: blind, cup-shaped end of renal tubule 3. Renal Corpuscle: a glomerulus and its Bowman’s capsule 4. Glomerular Endothelium: epithelium that allows solute-rich, protein-free filtrate to pass from blood into collecting tubule resorbs water and solutes from filtrate and secretes substances into it functions more in secretion than absorption maintains acid/base balance and salt/water balance
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2 Capillary Beds •Every nephron has two capillary beds •Glomerulus •Peritubular capillaries •Each glomerulus is: •Fed by an afferent arteriole •Drained by an efferent arteriole •Blood pressure in the glomerulus is high because: •Arterioles are high-resistance vessels •Afferent arterioles have larger diameters than efferent arterioles •Fluids and solutes are forced out of the blood throughout the entire length of the glomerulus
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3 Juxtaglomerular Apparatus (JGA) Where the distal tubule lies against the afferent (sometimes efferent) arteriole Arteriole walls have juxtaglomerular (JG) cells Enlarged, smooth muscle cells Have secretory granules containing renin Act as mechanoreceptors Macula densa Tall, closely packed distal tubule cells Lie adjacent to JG cells Function as chemoreceptors or osmoreceptors
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4 Mechanism of Urine Formation Urine formation and adjustment of blood composition involves three major processes Glomerular filtration movement of fluid and solutes from glomerular capillaries into Bowman’s space Tubular reabsorption movement of materials from filtrate in tubules into peritubular capillaries Secretion secretion of solutes from peritubular capillaries into tubules
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5 Net Filtration Pressure (NFP) The glomerulus is more efficient than other capillary beds because: Its filtration membrane is significantly more permeable Glomerular blood pressure is higher It has a higher net filtration pressure Plasma proteins are not filtered and are used to maintain oncotic pressure of the blood NFP (the pressure responsible for filtrate formation) equals the glomerular hydrostatic pressure (HP g ) minus the oncotic pressure of glomerular blood (OP g ) combined with the capsular hydrostatic pressure (HP c ) NFP = HP g – (OP g + HP c )
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6 Net Filtration Pressure (NFP)
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This note was uploaded on 09/02/2010 for the course OT 261 taught by Professor Howell during the Spring '07 term at USC.

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3-25 - The Nephron: blood processing unit functions more in...

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