58 Glomerular Filtration

58 Glomerular - PSL302 Lecture 58 by Perumalla Fri Mar 11 2011 Glomerular Filtration Outline Introduction to glomerular filtration Structure of

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Unformatted text preview: PSL302: Lecture 58, by Perumalla! Fri. Mar. 11, 2011 Glomerular Filtration Outline - Introduction to glomerular filtration - Structure of renal corpuscle - Filtration pressures - Hydraulic pressure of blood - Plasma colloid osmotic pressure - Bowman capsule's hydrostatic pressure - Factors affecting glomerular filtration rate (GFR) - Glomerular capillary blood pressure - Osmotic & hydrostatic pressures - Autoregulation (myogenic & tubuloglomerular) - Reflex control of GFR Introduction to glomerular filtration - Glomerular filtration - Is the first step to urine formation - Involves the transfer of fluid from the blood into the kidney tubule by filtration - Is relatively non-specific process - Creates a filtrate much like interstitial fluid or the plasma w/o the plasma proteins - Under normal circumstances, results in a filtrate consisting of water & dissolved solutes - Will not allow plasma proteins & blood cells from being filtered Structure of renal corpuscle 1. The glomerular capillary endothelium 2. The basal lamina (basement membrane) 3. The epithelium of Bowman's capsule 5 1. Glomerular capillary endothelium: capillary pores 4 - In glomerular capillary wall, endothelial cells are perforated by large holes, called fenestrae - Fenestrae are small enough to exclude blood cells & plasma proteins 2. Basement membrane - An acellular layer called the basal lamina separates the capillary endothelium from the epithelial lining of the Bowman's capsule 1 of 5 PSL302: Lecture 58, by Perumalla! Fri. Mar. 11, 2011 - Composed of collagen, glycoproteins & albuminuria (protein in urine) Basement Membrane An acellular layer called the basal lamina separates the capillary endothelium from the epithelial lining of the Bowman's capsule. Composed of collagen and glycoproteins Albuminuria (protein in the urine) 3. Epithelium of Bowman's capsule: filtration slits - Consists of specialized cells called podocytes 7 - In btwn podocytes, narrow slits are present - The size of the filtration slits can be varied by the contraction of mesangial cells in the basal lamina Filtration pressures ! Hydraulic pressure of blood: Glomerular capillary blood pressure - Glomerular Capillary Blood Pressure Is the fluid pressure exerted by blood WITHIN glomerular capillaries (Hydraulic Pressure of Blood) - Major force responsible for filtration = ~55mmHg Is the fluid - Favours by pressure filtration exerted blood within the Glomerular capillaries Major force responsible for filtration ~ 55 mm Hg FAVOURS FILTRATION !Plasma Colloid Osmotic Pressure Plasma colloid osmotic pressure - Caused by unequal distribution of plasma proteins across glomerular membrane = ~30mmHg - Opposes by the unequal filtration Caused 9 distribution of plasma proteins across the Glom. Membrane ~ 30 mm Hg OPPOSES FILTRATION ! Bowman capsule's hydrostatic pressure -Plasma Colloid Osmotic Pressure Bowman's capsule: enclosed space - Presence of fluid w/i capsule creates fluid pressure = ~15mmHg - Opposes by the unequal filtration Caused 10 distribution of plasma proteins across the Glom. Membrane ~ 30 mm Hg OPPOSES FILTRATION 10 2 of 5 PSL302: Lecture 58, by Perumalla! Fri. Mar. 11, 2011 Factors affecting glomerular filtration rate (GFR) 1. Glomerular capillary blood pressure 2. Plasma-colloid osmotic pressure & Bowman's capsule's hydrostatic pressure 3. Autoregulation: myogenic, tubuloglomerular feedback 4. Reflex control of GFR 12 ! 1. Glomerular capillary blood pressure - Depends on contraction of heart & resistance offered by afferent & efferent arterioles ! 2. Osmotic & hydrostatic pressures - [PP] osmotic pressure GFR - I.e. Severely burnt patients lose lg quantities of protein-rich plasma-derived fluid thru the exposed burned surface of their skin = GFR - [PP] OP GFR - I.e. Dehydrating diarrhea = loss of fluid ! 3. Autoregulation (myogenic & tubuloglomerular) - Autoregulation of GFR is a local control process in which the kidney maintains a relatively constant GFR in the face of normal fluctuation in BP - Two mechs: myogenic, tubuloglomerular feedback (a) Myogenic: intrinsic ability of vascular smooth muscle to respond to P - BP provides the hydrostatic pressure that drives glomerular filtration - in arterial BP glomerular capillary BP = GFR - in arterial BP glomerular capillary BP = GFR 18 19 20 3 of 5 PSL302: Lecture 58, by Perumalla! Fri. Mar. 11, 2011 (a) Tubuloglomerular feedback: ! 4. Reflex control of GFR 21 - Systemic signals (i.e. hormones & ANS) also affect the GFR by changing resistance in arterioles or by altering filtration coefficient - Integrating centers outside the kidney initiate these signals, often in response to systemic BP or V - Both afferent & efferent arterioles are innervated by sympathetic neurons that terminate on -receptors - Activation of these receptors = vasoconstriction regulate the GFR SHORT TERM CHANGES BP Baroreceptor reflex Exercise LONG TERM CHANGES Sympathetic Nerve Activity CO Vasoconstriction Skin, GI GFR Vasoconstriction of afferent arteriole in kidney Urine Production TPR Conservation of Fluids & salt Blood Volume 23 4 of 5 PSL302: Lecture 58, by Perumalla! Fri. Mar. 11, 2011 24 5 of 5 ...
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This note was uploaded on 03/27/2012 for the course PSL 301 taught by Professor Mackayfrench during the Winter '12 term at University of Toronto- Toronto.

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