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1. Renal Functions & Glomerular Filtration

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1. Renal Functions & Glomerular Filtration gmail.com 1. Renal Functions & Glomerular Filtration @ 434 434 Physiology Team Physiology physiology : us contact Color index 1 - Important - Further Explanation Contents Recommended Videos! Kidney Functions........................................................3 Nephron Structure.....................................................4 Renal Blood Vessels...................................................7 Renal Blood Flow.......................................................8 Urine Formation..........................................................9 Glomerular Membrane...........................................11 Glomerular Filtration Rate ......................................13 Starling’s Forces .......................................................14 Changes in Forces ..................................................15 Afferent & Efferent Arteriolar Resistance Affect...16 Factors Affecting Renal Blood Flow & GFR...........18 Composition of Glomerular Filtration.....................20 Innervation of the kidney........................................20 Summary...................................................................21 Questions..................................................................23 2 Please check out this link before viewing the file to know if there are any additions/changes or corrections. The same link will be used for all of our work Physiology Edit Kidney Functions Filter 200 liters of blood daily, from toxins, metabolic wastes Regulation of : Water and electrolyte balance. Arterial blood pressure. Body fluid osmolality & electrolytes. Acid/base balance Excretion of : Waste products : Urea Creatinine Uric Acid Bioactive substances such as hormones and many foreign substances, especially drugs. Synthetic Functions : Active form of vit D = 1,25 dihydroxychlicalciferol Erythropoietin production Renin formation 3 Synthesis of glucose from amino acids during prolonged fasting What is The Functional & structural Unit of The Kidney? The Nephron Each kidney has 1 million nephrons, each nephron is capable of urine formation. Structure of a Nephron o The Glomerulus: which is the capillary tuft: in which large amount of fluid is filtered from blood. o Bwaman’s capsule: Around the glomerulus and receives the filtrate. o Tubules: in which filtered fluid eventually is converted into urine. 4 Renal Tubules Proximal convoluted tubule (in cortex) composed of 1- microvilli 2-cobodial cells and mitocndia Function : Reabsorbs water and solutes from filtrate and secretes substances into it Loop of Henle smellier to Proximal convoluted tubule Distal convoluted tubule (in renal cortex) composed of cuboidal cells without microvilli Function : more in secretion than reabsorption Types of Nephrons Cortical nephrons (85%) Located in the cortex – Short loop of Henle. Juxtamedullary nephrons: (15%) Located in the cortex-medulla junction Long loops of Henle that deeply invade the medulla. 5 Maintain salt gradient, help conserve water. Cortical Loop on Henle 6 Renal Blood Vessels 2 3 2 1 Lecture 1 Afferent Deliveries blood into Arteriole glomeruli AS IN ARRIVING 2 Glomerular Produces filtrate that Capillaries enters the tubules Deliveries blood from 3 Efferent glomeruli to peritubular Arteriole capillaries 4 Mentioned in Males’ Slides of AS IN EXITING 7 4 Peritubular Vasa recta Which are long, hairpin-shaped blood vessels Capillaries Renal Blood Flow 2 Renal blood flow to the kidney represents 20% of cardiac output The blood flow to each kidney through a renal artery Lecture Features of Renal Circulation High blood flow (1200 ml/min) Such high rate of RBF are not surprising in light of the central role the kidneys play in maintaining the volume and composition of fluids! 20% Presence of 2 capillary beds: Glomerular & Peritubular. Efferent and afferent arterioles are Mentioned in Males’ Slides of major sites of resistance Due to the high pressure in those 2 arterioles. 8 Urine Formation 2 Primary function of the kidney is to ‘clear’ unneeded substances from the blood to be excreted in urine Lecture Steps of Urine Formation (Renal Processes) 1. Filtration 1 Glomerular Filtration 2 Tubular Reabsorption 22 . Reabsorption 3 Tubular Secretion 3. Secretion Mentioned in Males’ Slides of 4 Excretion 44 . Excretion 9 Urinary Excretion Rate = Filtration Rate – Reabsorption + Secretion cont. Urine Formation 1 Glomerular Filtration 2 Tubular Reabsorption 3 Tubular Secretion 4 Urine Excretion 2 Movement of substances from The first step in urine tubular lumen back into the blood formation “The end product” Reabsorbed substances not lost in The selective transfer of Lecture Blood flows through the the urine, but are carried by the substances from the The elimination of glomerulus, allowing peritubular capillaries to the venous peritubular capillary into substances from the protein-free plasma to be system the tubular lumen body in the urine filtered through the glomerular capillaries into Most of the filtered plasma is the Bowman’s capsule. reabsorbed Types o Transcellular (across the cell) o Paracellular (between cells) Allows for rapid o Active substances that are All plasma constituents elimination of substances needed by the body (via primary filtered or secreted, but in Males’ Slides of from the plasma via 20% of plasma entering active transport based on ATP not reabsorbed remain extraction of the 80% of the glomerulus is filtered hydrolysis (e.g. Na+) or secondary in the tubules and pass unfiltered plasma in active transport based on an ion into the renal pelvis to peritubular capillaries and Only 125 ml/min filtered fluid gradient (e.g. glucose) be excreted as urine adding it to the o Passive Bulk flow results from the and eliminated from substances already in the body imbalance of osmotic or hydrostatic tubule as result of filtration 10 forces at the peritubular capillary. Exactly the same as at the peripheral capillary or the glomerulus Glomerular Membrane It’s where the first step in renal processing occur which involves the filtration of plasma in the glomerulus Composed of three layers : 1- Endothelium of the glomerular capillaries : it is fenestrated and the pores are about 50 – 100 nm in diameter. 2- Basement membrane : composed of fused basal laminae of the other layers. 3- Epithelial membrane : visceral membrane of glomerular capsule ( podocytes ). Filtration Membrane : Filter that lies between the blood and the interior of the glomerular capsule. 11 Glomerular Membrane cont. - Glomerular filtration membrane is highly permeable to water and small molecules (less than 10.000 MW). - Large molecules (more than 70.000 MW especially proteins are not filtered due to: 1- Their large size. 2- Negative electrical charge, because their passage is repulsed by negatively charged glycoproteins present on endothelial pores, basement membrane and podocytes. ( they will be repelled by negative charge in the membrane ) 12 Glomerular Filtration Rate (GFR) 2 The rate of production of filtrate at the glomeruli from plasma per minute = 20% of RPF* 99% of filtrate reabsorbed, 1 to 2 L urine excreted GFR is determined by: Lecture NFP = 10 NORMAL VALUES Kf = 12.5 1: The Net Filtration 2: The glomerular Pressure across the capillary filtration glomerular capillaries coefficient Starling’s Forces Surface Area Permeability 1 2 Mentioned in Males’ Slides of GFR = NFP x Kf NORMAL GFR WILL BE : 13 GFR = 10 x 12.5 = 125 ml/min = 180 L/Day * Renal Plasma Flow Forces Controlling GFR Opposes Filtration 2 Promotes Filtration Starling’s Forces The Net Filtration Pressure (NFP) is the sum of Lecture Pc Glomerular Hydrostatic Pressure = 60 mmHg Colloid Osmotic Pressure of Glomerular plasma proteins NFP ✖ = 32 mmHg b = 0 Pb Bowman’s Hydrostatic Pressure = 18 mmHg As we knew that filtration membrane doesn't allow proteins to pass therefore Colloid Osmotic Pressure of bowman's space has NO Bowman’s proteins proteins which means = 0 mmHg oncotic pressure = 0 Mentioned in Males’ Slides of 14 NFP = (P -P ) - ( - ) C b c b Recall! NFP = ( 60 – 18 ) – (32 – 0) = 10 mmHg GFR = NFP x Kf = 10 x 12.5 = 125 ml/min Changes in Forces & Affection of GFR 2 Increased Pc Increases GFR. This pressure is affected by: ABP, Afferent & Efferent arteriolar resistance’ Lecture ‘: Constriction or dilation Increased c Decreases GFR in which plasma proteins are Mentioned in Males’ Slides of increased. Increased Pb Decreases GFR 15 In urinary obstruction e.g. stones or tumors. Pc = Glomerular hydrostatic pressure Pb = Bowman’s hydrostatic pressure = Colloid osmotic pressure of glomerular plasma proteins Afferent & Efferent Arteriolar Resistance Affect 2 As vasodilation and vasoconstriction of the afferent and efferent arterioles alter the blood flow through the glomerular capillaries, there are corresponding alterations in the glomerular filtration rate (GFR). Lecture Constriction of Constriction of Efferent Afferent E.g.: Angiotensin II E.g.: Sympathetic o PGC o PGC o GFR o GFR Dilation of Dilation of Efferent Afferent o PGC o PGC Mentioned in Males’ Slides of o GFR o GFR 16 PGC = Glomerular Hydrostatic Pressure Cont. To sum up the previous discussion on the changes which occur to RBF and GFR under different parameters.. Parameter RPF Pc c GFR Afferent Constriction NC Note: if severe Afferent Dilation NC vasoconstriction occur to the Moderate efferent the blood Efferent Constriction NC moves so slowly where GFR Severe increases and the Efferent Constriction - blood is almost completely filtered Efferent Dilation NC and the
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