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50 intertwining capillaries; blood delivered via afferent arteriole& leaves in efferent arteriole goes to peritubular capillaries then small venules & returns blood to venous systemFiltration in renal corpuscle; BP forces H2O & dissolved solutes out of glomerular capillaries into capsular space; produces protein-free solution (filtrate) similar to blood plasmaThree Functions of Renal Tubule 0.Reabsorb useful organic nutrients that enter filtrate0.Reabsorb more than 90% of H2O in filtrate0.Secrete waste products that failed to enter renal corpuscle through filtration at glomerulusProximal convoluted tubule (PCT) & Distal convoluted tubule (DCT); separated by loop of Henle; U-shaped tube that extends partially into medulla; otherwise all renal tubule in cortexOrganization of Nephron: filtrate gradually changes composition along tube; changes vary with activities in each part of nephron; each nephronempties into the collecting system: a series of tubes that carries tubular fluid away from nephronCollecting Ducts receive fluid from many nephrons; each collecting duct begins in cortex, descends into medulla &carries fluid to papillary ductthat drains into a minor calyxTwo Types of Nephrons1. Cortical Nephrons: 85%; mainly in cortex of kidney; Loop of Henle is relatively short; efferent arteriole delivers blood to a network of peritubular capillaries2.Juxtamedullary Nephrons: 15%; nephron loops extend deep into medulla; peritubular capillaries connect to vasa rectaRenal CorpuscleGlomerular capsule connected to beginning of renal tubule; forms outer wall that encapsulates glomerular capillaries (Glomerulus); outer wall lined by simple squamous epithelium, continuous with visceral epitheliumwhich covers glomerular capillaries; separated by capsular spaceVisceral Epithelium consists of large cells (podocytes) with complex processes or “feet” (pedicels) that wrap around specialized lamina densa of glomerular capillariesFiltration Slitsare narrow gaps between adjacent pedicels; materials passing out of blood at glomerulus must be small enough to pass between filtration slits Glomerular Capillaries are fenestrated capillaries; endothelium contains large-diameter poresBlood Flow Control: special supporting cells (mesangial cells) between adjacent capillaries control diameter and rate of capillary blood flowFiltration: BPforces H2O & small solutes across membrane into capsular spaceFiltration at Renal Corpuscle is passive; solutes enter capsular space: metabolic wastes, excess ions, glucose, free fatty acids, amino acids & vitaminsReabsorption: preventsuseful materials from leaving kidneys; reabsorption occurs in PCT. PCTis 1stsegment of tubule; entrance lies opposite afferent & efferent arterioles at glomerulusEpithelial Lining of PCT: simple cuboidal with microvilli; reabsorption & secretion Tubular Cells absorb organic nutrients, ions, water & plasma proteins from tubular fluid: release them into peritubular fluid (interstitial fluid around renal tubule)Loop of Henle: each limb contains a