50 intertwining capillaries blood delivered via afferent arteriole leaves in

50 intertwining capillaries blood delivered via

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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 system Filtration in renal corpuscle; BP forces H 2 O & dissolved solutes out of glomerular capillaries into capsular space; produces protein-free solution (filtrate) similar to blood plasma Three Functions of Renal Tubule 0. Reabsorb useful organic nutrients that enter filtrate 0. Reabsorb more than 90% of H 2 O in filtrate 0. Secrete waste products that failed to enter renal corpuscle through filtration at glomerulus Proximal 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 cortex Organization of Nephron: filtrate gradually changes composition along tube; changes vary with activities in each part of nephron; each nephron empties into the collecting system : a series of tubes that carries tubular fluid away from nephron Collecting Ducts receive fluid from many nephrons; each collecting duct begins in cortex, descends into medulla & carries fluid to papillary duct that drains into a minor calyx Two Types of Nephrons 1. Cortical Nephrons: 85%; mainly in cortex of kidney; Loop of Henle is relatively short; efferent arteriole delivers blood to a network of peritubular capillaries 2. Juxtamedullary Nephrons: 15%; nephron loops extend deep into medulla; peritubular capillaries connect to vasa recta Renal Corpuscle Glomerular capsule connected to beginning of renal tubule; forms outer wall that encapsulates glomerular capillaries ( Glomerulus); o uter wall lined by simple squamous epithelium , continuous with visceral epithelium which covers glomerular capillaries; separated by capsular space Visceral Epithelium consists of large cells ( podocytes ) with complex processes or “feet” ( pedicels ) that wrap around specialized lamina densa of glomerular capillaries Filtration Slits are 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 pores Blood Flow Control: special supporting cells ( mesangial cells ) between adjacent capillaries control diameter and rate of capillary blood flow Filtration: BP forces H 2 O & small solutes across membrane into capsular space Filtration at Renal Corpuscle is passive; solutes enter capsular space: metabolic wastes, excess ions, glucose, free fatty acids, amino acids & vitamins Reabsorption: prevents useful materials from leaving kidneys; reabsorption occurs in PCT. PCT is 1 st segment of tubule; entrance lies opposite afferent & efferent arterioles at glomerulus Epithelial 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
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