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NORTH BIOL& 242 - Urinary System I: Kidneys and Urine Formation

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Urinary System I Kidneys and Urine Formation Functions of the Urinary System Organs of the Urinary System The Kidney Coverings and Regions Blood Flow Nephrons Glomeruli and Renal Tubules Urine Formation Urinalysis Ureters Bladder and Urethra Functions of the Urinary System Blood Filtration Elimination of waste products Nitrogenous wastes amino groups from amino acids Toxins Drugs Regulate aspects of homeostasis Water balance Electrolytes Acid base balance in the blood Blood pressure Red blood cell production erythropoietin Activation of vitamin D Organs of the Urinary system Kidneys Against the dorsal body wall At the level of T12 to L3 The right kidney is slightly lower than the left Retroperitoneal posterior to and outside of parietal peritoneum Attached to ureters renal blood vessels and nerves at renal hilus Covered with adipose Ureters Urinary bladder Urethra Coverings of the Kidneys Renal capsule Surrounds each kidney Adipose capsule Fascia layer adventitia connective tissue substitutes for serosae outside of peritoneal cavity Surrounds the kidney Provides protection to the kidney Helps keep the kidney in its correct location Regions of the Kidney Kidney Regions Renal cortex outer region Renal medulla inside the cortex Renal pelvis inner collecting tube Kidney Structures Medullary pyramids triangular regions of tissue in the medulla Renal columns extensions of cortex like material inward Calyces cup shaped structures that funnel urine towards the renal pelvis Blood Flow in the Kidneys Glomerular capillaries Peritubular capillaries Unique Incoming vessels enter as an arteriole narrow into a capillary bed in the glomerulus leave in an arteriole and then break into the peritubular capillary bed before leaving as venus blood The Nephron Glomerulus and Bowman s Capsule A specialized capillary bed Attached to narrow arterioles on both sides maintains high pressure in capsule Fenestrated glomerular endothelium Allows filtrate to pass from plasma into the glomerular capsule Filtration slits Layers of Bowman s capsule Parietal layer simple squamous epithelium Visceral layer branching epithelial podocytes o Extensions terminate in foot processes that cling to basement membrane o Filtration slits allow filtrate to pass into the capsular space Capsular space Renal Tubule Proximal convoluted tubule Loop of Henle Distal convoluted tubule Collecting duct Figure 15 3b Two Types of Nephrons Cortical nephrons Located entirely in the cortex Includes most nephrons 85 Cortex Juxtamedullary nephrons Found at the boundary of the cortex and medulla Important in the production of concentrated urine Medulla Juxtaglomerular Apparatus JGA Macula densa sensors of the filtrate Tall closely packed cells lining the ascending Lof H or PCT Water and NaCl concentration detected by osmo and chemoreceptors If filtrate water volume then stimulation of renin release by JG blood water volume blood pressure If NaCl in PCT filtrate dilation of afferent arteriole reduce filtration rate Na stays in filtrate by tubules blood Na If NaCl in PCT filtrate then renin release by JG blood water volume blood pressure Granular cells juxtaglomerular or JG cells pressure sensors of incoming blood and storage of renin Enlarged smooth muscle cells of blood afferent arteriole Secretory granules release renin when epi NE in blood Act as mechanoreceptors that sense low blood pressure Responds to stimuli by macula densa Extraglomerular mesangial cells Peritubular Capillaries Arise from efferent arteriole of the glomerulus Cling to adjacent renal tubules in cortex Low pressure porous capillaries adapted for absorption Reabsorb reclaim some substances from collecting tubes Empty into venules Vasa recta are the long vessels parallel to long loops of Henle Filtrate efferent afferent arterioles Water is reclaimed from filtrate into venous circulation via peritubular capillaries Epithelia in the Tubules Are Designed for Filtration and Absorption Glomerular capsule parietal layer Renal cortex Renal medulla Basement membrane Renal corpuscle Glomerular capsule Glomerulus Renal pelvis Podocyte Distal convoluted tubule Ureter Kidney Fenestrated endothelium of the glomerulus Glomerular capsule visceral layer Microvilli Proximal convoluted tubule Highly infolded plasma membrane Proximal convoluted tubule cells Cortex and thick ascending L 0f H Medulla Thick segment Thin segment Loop of Henle Descending limb Ascending limb Mitochondria Distal convoluted tubule cells Collecting duct Loop of Henle thin segment cells Principal cell Mostly cuboidal epithelium with modifications in membrane surfaces Intercalated cell Collecting duct cells Figure 25 5 Urine Formation Processes A Filtration Nonselective passive process Water and solutes smaller than proteins are forced through capillary walls no cells essentially plasma Filtrate is collected in the glomerular capsule and leaves via the renal tubule Blood pressure relatively high in glomerulus Efficient filtration driven by hydrostatic pressure B Tubular Reabsorption The peritubular capillaries reabsorb several materials H2O glucose amino acids ions Some reabsorption is passive most is active Nitrogenous waste products not reabsorbed nor excess water urea uric acid or creatinine Most reabsorption occurs in the proximal convoluted tubule C Tubular Secretion Some materials pumped from the peritubular capillaries into the renal tubules H K creatinine Materials left in the renal tubule move toward the ureter Net Filtration Pressure NFP at the Glomerulus Afferent arteriole Glomerular capsule NFP HPg OPg HPc push outwards back pressure inwards 10 mm Hg Net filtration pressure Glomerular blood hydrostatic pressure HPg 55 mm Hg Blood colloid osmotic pressure Opg 30 mm Hg Capsular hydrostatic pressure HPc 15 mm Hg Figure 25 11 Glomerular Filtration Rate Volume of filtrate formed per minute by the kidneys 120 125 ml min Governed by and directly proportional to Total surface area available for filtration Filtration membrane permeability Flow rate GFR is tightly controlled by two types of mechanisms o Intrinsic controls renal autoregulation o Extrinsic controls nervous and endocrine regulation Intrinsic Controls Renal Autoregulation of GFR Local action within the kidney Myogenic mechanism BP constriction of afferent arterioles Helps maintain normal GFR Protects glomeruli from damaging high BP BP dilation of afferent arterioles Helps maintain normal GFR Tubuloglomerular feedback mechanism which senses changes in the


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