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Introduction • Cellular metabolism produces wastes Chapter 25 – CO2 – Urea – Ammonia • Kidneys rid the body of most nitrogenous wastes • Kidneys regulate the chemical make-up of blood The Urinary System General Functions • Serves as a blood filter • Toxins, metabolic wastes leave the body in urine • H2O, glucose, and amino acids are returned to blood Organs of the Urinary System • Kidneys (paired) – Perform filtering functions and manufacture urine • Ureters (paired) – Transport urine • Urinary bladder (single) – Stores urine • Urethra (single) – Transports urine Human Anatomy, 3rd edition Prentice Hall, © 2001 Location of the Kidneys • Lie against the dorsal body wall • Beneath the parietal peritoneum • In the superior lumbar region – Protected by the lower part of the rib cage Human Anatomy, 3rd edition Prentice Hall, © 2001 Anatomy of the Kidney • External Anatomy – Hilus – Renal capsule – Renal artery – Renal vein – Ureter • Internal Anatomy – Renal cortex – Renal medulla • Renal pyramids • Renal papilla – Renal pelvis – Calyces Human Anatomy, 3rd edition Prentice Hall, © 2001 1 Blood Supply of the Kidney • Approximately ¼ of the total blood supply passes through the kidneys each minute • Renal artery branches Nephrons and Urine Formation • Nephrons form the urine product – Filtration – Reabsorption – Secretion – Supplies pyramids and cortex • Each kidney contains about 1 million nephrons • Venous blood leaves the cortex and medulla – Small veins join the renal vein Human Anatomy, 3rd edition Prentice Hall, © 2001 Structure of a Nephron • 2 main structures – Glomerulus – Renal tubule • Bowman’s capsule • Proximal convoluted tubule • Henle’s Loop • Distal convoluted tubule Human Anatomy, 3rd edition Prentice Hall, © 2001 The Glomerulus - Filtration • Blood enters glomerulus – Afferent arteriole • Glomerulus filters blood – Forms filtrate • Blood leaves glomerulus • Collecting duct – Receives urine from nephrons – Delivers final urine Anatomy, 3rd edition product into calyces Human Prentice Hall, © 2001 Renal Tubule – Reabsorption & Secretion • Reabsorption – Efferent arteriole Human Anatomy, 3rd edition Prentice Hall, © 2001 Control of Blood Composition • Excretion of nitrogen-containing compounds – Substances move from filtrate into peritubular capillaries • Active transport • Most occurs in proximal convoluted tubule – Urea – Uric acid • Water and electrolyte balance – Regulated by hormones • Secretion – Substances move from peritubular capillaries into filtrate – Control of blood pH http://home.earthlink.net/~dayvdanls/nephron.gif 2 Summary of Urine Flow • Kidneys produce urine – Filtration – Reabsorption – Secretion • Ureters • Bladder • Urethra www.foxriverwatch.com/kidney_works.jpg 3