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Renal Physiology.docx

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Western University
Physiology 2130

Renal Physiology 7 Major Functions of the Kidneys: 1) Regulation of extracellular fluid volume and blood pressure 2) Regulation of osmolality 3) Maintain ion balance 4) Maintain pH 5) Excretion of wastes 6) Production of hormones 7) Gluconeogenesis - we each have 2 bean shaped kidneys located posteriorly to the abdomen, one on each side of the spine at the level of the 11 and 12 rib - blood enters and exits the inner (concave) side of each kidney - the exit of the ureter comes from the inner side of each kidney, which carries urine from the kidney to the bladder The Nephron: - is a functional unit of the kidney - each kidney has aprox 1mill nephrons - 80% of nephrons are located in the cortex layer of the kidney - other 20% of nephrons are called juxtamedullary nephrons (dip into medulla) 2 Main Types of Nephrons: 1) Cortical: shorter loop of henle, located in the renal cortex, majority of neprhons are cortical 2) Juxtamedullary: long loop of henle, dip down into medulla, allows for creation of concentrated urine - Every nephrons (cortical and jux) renal corpuscle is located in the cortex of the kidney - The renal corpuscles give the cortex of the kidney a granular appearance 2 Main Structures of the Corpuscle: 1) Bowmans capsule: fluid filled ball-like structure that surrounds the glomerulus. The glomerulus is fused to bowmans capsule via basal lamina, which is made up of collagens and negatively charged glycoproteins 2) Glomerulus: specialized capillaries with “leaky” special pore properties. Covered by podocytes, which wrap around leaky capillaries. Further filtration, everything besides red blood cells can filter out Podocytes: specialized cells that surround the glomerulus capillaries and connected to the basal lamina, third filtering component of the renal corpuscle 3 Barriers to Filtration: 1) Cells (endothelial) of the capillary 2) Basal Lamina 3) Podocytes - substance must filter thru all 3 barriers to get into bowmans space Filter to Bowmans: water, glucose, amino acids, CO2, O2, hydrogen, ions (Na, Cl, K) Wont Filter: red and white blood cells, most (pretty much all) proteins Major Components of Blood: 1) Plasma (mostly made of water) - contains dissolved proteins, glucose, ions, hormones, CO2, 02, H 2) Blood cells - red and white Blood flows from heart: heart- artery- arterioles- capillaries- venules- veins- heart. Blood flow in kidneys (different): renal artery- affrent arteriole- glomerular capillaries- efferent arteriole- peritubular capillaries- venule renal vein 3 Processes of the Nephron: - kidneys filter 180L plasma a day, only excrete 1.5L urine therefore most of filtrate is reabsorbed 1) Filtration: Occurs in renal corpuscle, movement of plasma (and solutes dissolved in them) from the blood to Bowman’s capsule. Everything filtered in Bowmans will be excreted unless reabsorbed. (water, ions, glucose, amino acids, creatine, urea can filter) 2)Reabsorption: move substances from filtrate as it travels through the tubule back into the blood (via peritubular or vasa recta capillaries) 3)Secretion: movement of selected molecules from the blood in the peritubular capillaries to the filtrate as it travels through the tubule. (ie. Drugs) - the filtrate that leaves the nephron (excretion) it termed the urine, made up of the processes listed above - excretion= reabsorption + secretion Glomerular filtration and Blood Flow: - 20% of the cardiac output goes to the kidney - 20% of the blood volume will actually filter into bowmans space - what are the forces that cause filtration? 4 pressures that affect glomerular filtration: 1) Hydrostatic Pressure (P GC): pressure of blood flowing through glomerular capillaries forces fluid out.55mmHg 2) Colloid Osmotic Pressure (TT GC): pressure created due to presence of proteins. Most proteins stay in glomerular capillaries so higher pressure here. 30mmHg 3) Hydrostatic Pressure (P BC): pressure of fluid already in Bowman’s capsule creates a back pressure. 15mmHg 4) Colloid Osmotic Pressure (TT BC): Pressure created due to presence in Bowmans…but almost no protein in bowmans. 0mmHg Net Filtration pressure =(PGC+TTBC) – (PBC+TTBC) =PGC-PBC-TTGC = 55mmHg- 15mmHg- 30mmHg 10mmHg - if value larger that 10, more filtration, if less than less filtration Glomerular Filtration Rate: the amount of fluid (with dissolved substances) that filters into Bowmans capsule per unit time. If GFR increases, increase excretion of salt and water in the urine. 2 Factors Affecting GFR: 1) Net filtration pressure: influences by renal blood flow, and blood pressure 2) Filtration Coefficient: influenced by surface area of glomerular capillaries available for filtration and permeability of barriers between capillary and bowmans space Regulation of GFR: blood pressure provides hydrostatic pressure needed for glomerular filtration, but if overall blood pressure fluctuates we have two internal mechanisms in our body used to maintain GFR. 1) myogenic response:  increase of blood pressure  smooth muscle in afrent arteriole stretch  stretch sensitive ion channels open  muscle cells depolarize  VG Ca channels open  Smooth muscle cells contract  Decrease blood flow in glomerulus; 2) Tubuloglomerular feedback:  The composition of the filtrate can regulate GFR  The distal convoluted tubule passes between the affrent and efferent arteriole  The macula densa are specialized cells in this part of the tubule  Cells in the macula densa detect levels of NaCl in filtrate  If the concentration too high (can be due to increase in GFR)  Chemical signal released locally that causes the affrent arteriole to constrict therefore reducing blood flow and GFR  GFR is mostly controlled by the regulation of blood floe through renal arterioles  If resistance (constriction) occurs in the afferent arteriole, hydrostatic pressure_________, therefore GFR__________.  If resistance (constriction) occurs in the efferent arteriole, hydrostatic pressure_________, therefore GFR__________. How do we Measure GFR? - rate of excretion = rate of filtration - So, pick substance to measure in the urine that 1. Freely flows into bowmans 2. Is not reabsorbed 3. Is not secreted - Eg. Creatinine, constantly produced, feely flows to bowmans and is not reabsorbed, tiny amount secreted (not perfect molecule) - Creatinine clearance rate= Creatinine excretion rate + Creatinine plasma - GFR=Creatinine clearance rate Renal Handling: once we k
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