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Lecture 16

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Biological Sciences
Stephen Reid

BIOC34 Lecture 16 - The Renal System and Kidney Function Pressures Driving Fluid In and Out of Capillaries - two important pressure gradients - hydrostaticpressuregradient - pressure exerted by presence of fluid in system - within capillary - equal to the blood pressure within that capillary - within ECF - equal to pressure exerted by the presence of fluid in space - oncoticpressuregradient Hydrostatic Pressure Gradients - calculated - Hydrostatic pressure within a capillary - hydrostatic pressure of the interstitial fluid (usually 1 mmHg) - venous side - pressure in capillary is lower ~16 mmHg - pressure gradients tend to force fluid out of the capillary and into the extracellular fluid - both positive pressures with the driving force directed out of the capillary Oncotic Pressure Gradients - osmotic pressure exerted by the presence of proteins - interstitial fluid has no proteins - there are proteins in blood plasma - pressure ~25 mmHg - proteins too large to diffuse out of the capillary walls - pressure equal throughout capillary bed Net Filtration Pressure - hydrostatic pressures “push” fluid from an area of hydrostatic pressure to an area of low hydrostatic pressure - oncotic pressures “pull” fluid - arterial end of capillary - hydrostatic pressure is higher than the oncotic pressure - venous end of capillary - hydrostatic pressure less than oncotic pressure - lead to fluid movement across capillary - calculated - hydrostatic pressure gradient - oncotic pressure - positive NFP cause filtration - negative NFP cause absorption - arterial side tends to filter out into the interstitial fluid - venous side, fluid tends to absorb back into capillary - whole body perspective - 20 L a day of fluid is filtered across capillaries into ECF - only 17 liters is absorbed back into the capillaries from the ECF - remaining 3 liters returned to circulation by lymphaticsystem - consists of separate lymphatic capillaries that have open ends BIOC34 Lecture 16 - The Renal System and Kidney Function - absorb excess fluid from the extracellular space and return it to the vena cava and back into the circulation - pressures and pressure gradients drive the filtration of fluid (plasma) at the kidneys to form the fluid that becomes pre-urine Kidney Functions Gross Anatomy - kidneys under adrenal glands - blood supplied by renal artery, removed by renal vein - urine leaves kidney through ureter and enters the bladder - kidney made of sections called renal pyramids - outer section of the kidney referred to as renalcortex - inner region is the renalmedulla - in between renal pyramids, within inner region of kidney - space called minorcalyx - each connects to hollow core of kidney - renalpelvis - acts as a collecting area - convey fluid to renal pelvis - collects before draining down the ureter into the bladder Nephron - functional unit - consists of number of regions - begins in capillary bed called glomerulus - each glomerulus sits in glove-like structure - Bowman’sCapsule - fluid moves from glomerulus -> Bowman’s Capsule -> proximaltubule->(pre-urine) Loop ofHenle-> distalconvolutedtubule-> connecting tube -> collecting duct - proximal tubule - two sections - convoluted section - straight section - absorption of substances as well as sodium handling - Loop of Henle - responsible (in conjunction with vasa recta) for producing the osmotic gradient of the kidney - necessary for creating concentrated urine - two types of nephrons - cortical - juxtamedullary - Loop of Henle longer - reaches deep into renal medulla - responsible for creating the osmotic gradient in the kidney to produce concentrated urine Juxtaglomerular Apparatus BIOC34 Lecture 16 - The Renal System and Kidney Function - formed by glomerulus and Bowman’s Capsule - afferentglomerulararteriole - rings of smooth muscle - branches into capillary bed in glomerulus - blood leaves glomerulus through efferentglomerulararteriole - physical position ve
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