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BIOB32H3 (80)


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Biological Sciences
Kenneth Welch

The Urinary System An Overview of the Urinary System Functions of the urinary system •Excretion •The removal of organic waste products from body fluids •Elimination •The discharge of waste products into the environment •Homeostatic regulation of blood plasma •Regulating blood volume and pressure •Regulating plasma ion concentrations •Stabilizing blood pH •Conserving nutrients Urinary system includes: •The kidneys •Produce urine •The ureters •The urinary bladder •Stores urine •The urethra The kidneys •Left kidney extends slightly more superiorly than right •Both kidneys and adrenal glands are retroperitoneal •Hilus •Entry for renal artery and renal nerves •Exit for renal veins and ureter Sectional anatomy of the kidneys •Superficial outer cortex and inner medulla •The medulla consists of 6-18 renal pyramids •The cortex is composed of roughly 1.25 million nephrons •Major and minor calyces along with the pelvis drain urine to the ureters Blood supply and innervation of the kidneys •Renal arteries branch repeated •Renal artery •Segmental artery •Interlobar artery •Arcuate artery •Interlobular artery •Afferent arterioles •Renal venules follow similar opposing pattern ending with renal veins The nephron consists of a renal corpuscle and renal tubule •The renal corpuscle is composed of •Bowman’s capsule and the glomerulus •The renal tubule consists of •Proximal convoluted tubule (PCT) •Loop of Henle •Distal convoluted tubule (DCT) Filtrate is produced at the renal corpuscle •Nephron empties tubular fluid into collecting system •Collecting ducts and papillary ducts Nephron functions include: •Production of filtrate •Reabsorption of organic nutrients •Reabsorption of water and ions •Secretion of waste products into tubular fluid Two types of nephron •Cortical nephrons •~85% of all nephrons •Located in the cortex •Juxtamedullary nephrons •Closer to renal medulla •Loops of Henle extend deep into renal pyramids Renal tubule and blood flow •Blood travels from efferent arteriole to peritubular capillaries •Vasa recta •Renal tubule begins at renal corpuscle •Includes glomerulus and Bowman’s capsule •Blood leaves the nephron via the efferent arteriole Glomerulus anatomy •Podocytes cover lamina densa of capillaries •Project into the capsular space •Pedicels of podocytes separated by filtration slits Functional anatomy of the nephron •Proximal convoluted tubule (PCT) •Actively reabsorbs nutrients, plasma proteins and ions from filtrate •Released into peritubular fluid •Loop of Henle •Descending limb •Ascending limb •Each limb has a thick and thin section Functional anatomy of the nephron •Distal convoluted tubule (DCT) •Actively secretes ions, toxins, drugs •Reabsorbs sodium ions from tubular fluid Principles of Renal Physiology Urine production maintains homeostasis •Regulating blood volume and composition •Excreting waste products •Urea •Creatinine •Uric acid Basic processes of urine formation •Filtration •Blood pressure •Water and solutes across glomerular capillaries •Reabsorption •The removal of water and solutes from the filtrate •Secretion •Transport of solutes from the peritubular fluid into the tubular fluid Carrier Mediated Transport •Filtration in the kidneys modified by carrier mediated transport •Facilitated diffusion •Active transport •Cotransport •Countertransport •Carrier proteins have a transport maximum (T m •Determines renal threshold Reabsorption and secretion •Accomplished via diffusion, osmosis, and carrier-mediated transport •Tmdetermines renal threshold for reabsorption of substances in tubular fluid Renal function •Most regions of the nephron perform a combination of functions •General functions can be identified •Filtration in the renal corpuscle •Nutrient reabsorption along the PCT •Active secretion at PCT and DCT •Loops of Henle regulate final volume and solute concentration Renal Physiology: Filtration and the Glomerulus Filtration pressures - Glomerular filtration •Occurs as fluids move across the glomerulus
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