1Renal (Urinary) SystemChapter 17FunctionMaintains homeostasis in ECF • Removing metabolic waste (except CO2) – e.g. ammonia, urea, uric acid• Removing foreign compounds – e.g. drugs, food additives, pesticides• Regulating salt concentrations, fluid volume, and pH Anatomy• Kidneys (2)– process plasma into urine• Ureters (2)– tubes that carry urine to bladder• Urinary bladder– storage of urine• Urethra– carries urine to exteriorAnatomy• Cortex – outer granular region• Medulla – inner striated region – renal pyramids• Renal Pelvis– central collecting cavity• Renal artery and veinAnatomy• Nephron– 1 million per kidney– functional unit of the kidney – smallest unit capable of forming urineNephronVascular Component– conducts blood• Renal Artery • Afferent Arteriole• Glomerulus• Efferent Arteriole• Peritubular Capillaries • Venules• Renal Vein2NephronTubular Component– forms urine• Bowman’s capsule• Proximal Convoluted Tubule• Loop of Henle• Distal Convoluted Tubule • Collecting ductUrine Formation• Urine - water and waste solutes• Nephrons conduct three processes to convert blood plasma into urine1. filtration• filter blood plasma to retain cells/proteins2. reabsorption• remove valuable materials from filtrate3. secretion• transfer additional wastes to filtrateFiltration• Occurs in the glomerulus– Fenestrated capillaries•3 layers of podocytes form capillary walls• Small pores (fenestrae) – filters plasma • proteins + cells stay in blood•forms ultrafiltrateFiltration• Filtration driven by blood pressure• Glomerular filtration is non-selective – Small particles pass (glucose, Na+, urea, H2O) – Large ones do not• 20% of plasma enters tubule– plasma filtered 65x/dayReabsorption• Occurs in remainder of nephron tubule• Selective movement of substances from tubule into plasma– Return of valuable substances to peritubular caps• Active or passive– Passive (no energy)– Active transport (requires energy)Secretion• Also occurs in tubules• Additional materials transported from plasma in peritubular capillaries into tubule– excess K+, Ca2+and H+, uric acid– foreign compounds • By passive diffusion or active carrier transport3Proximal TubuleProximal Tubule Reabsorbs: • 2/3 of plasma Na+• 2/3 of plasma Cl-• 2/3 of plasma H2O• 100 % of plasma glucoseActive Transport in theProximal Tubule•Na+actively transported from cell to blood• Creates Na+gradient favoring Na+flow from lumen•Na+gradient used to transport glucose against concentration gradient (cotransport)• Glucose diffuses into blood passivelyPassive Reabsorption in theProximal Tubule•Cl-to be reabsorbed passively along electrical gradient• Water reabsorbed along osmotic gradientAcid Base Balance• Proximal tubule also secretes H+and absorbs HCO3-– used to regulate pH– with ↓ pH, ↑ H+secretion and HCO3-reabsorptionLoop of Henle• Kidneys produce a hyperosmotic urine– less H2O than blood plasma– concentrating mechanism occurs in the Loop of HenleLoop of Henle• Countercurrent Multiplication– generates osmotic gradient that draws H2O out of the tubules to be reabsorbed– due to active reabsorption of Na+& Cl-Exchange = 30Exchange = 504Loop of Henle• descending limb– permeable to water– no active transport• ascending limb– impermeable to water– lined w/ Na+-K+pumpsLoop of Henle• Pumping of ions out of ascending limb creates osmotic gradient• Water flows out of descending limb• Absorbed by peritubular capillaries• Fluid becomes more concentrated as it passes down descending limbLoop of Henle• Removal of ions without water causes fluid to become less concentrated in the ascending limb• Less concentrated than blood in distal convoluted tubule• 25% of initial Na+and water reabsorbed by loop of HenleDistal Convoluted Tubule and Collecting Duct• Secretion of K+and H+• Reabsorption of Na+ and water• Generation of hyperosmotic urine– final ~8% of water and Na+reabsorbedHormonal Regulation of Reabsorption• Aldosterone– increases Na+reabsorption and K+secretion by distal & collecting tubules – ↑ salt retention and BP (H2O retention)• ADH– induces implantation of aquaporins (water channels) into tubule cell membranes• ↑ permeability of Distal and Collecting tubules to water• ↑ H2O reabsorption = ↓ urine volumeTriggering of Aldosterone Release• release induced by juxtaglomerular apparatus– region of afferent arteriole that comes into contact w/ascending limb of Loop of Henle• releases renin (enzyme) into blood in response to ↓BP• renin converts angiotensinogen→ angiotensin I5Triggering of Aldosterone Release• angiotensin I converted to angiotensin II (fully activated) by angiotensin converting enzyme in lungs• angiotensin II stimulates aldosterone releaseUrination• Ureters– transfer urine to pelvic region• Urinary Bladder– Stores urine – smooth muscle, stretchable walls• Two sphincters– internal urethral sphincter(involuntary)– external urethral sphincter(voluntary)UrinationUrination Reflex:• Stretch receptors in bladder wall → spinal cord – efferents to smooth muscle →contraction• Internal sphincter relaxes• External sphincter