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Download Ch 15 Urine Formation
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THE URINARY SYSTEM: Urine Formation pages 516-519 © 2015 Pearson Education, Inc. URINE FORMATION The result of three processes: 1. 2. 3. Glomerular filtration Tubular reabsorption Tubular secretion FIGURE 15.4 THE KIDNEY DEPICTED SCHEMATICALLY AS A SINGLE LARGE, UNCOILED NEPHRON. Afferent arteriole Glomerular capillaries Efferent arteriole Cortical radiate artery 1 Glomerular capsule Rest of renal tubule containing filtrate 2 Peritubular capillary Three major renal processes: 1 2 3 To cortical radiate vein Urine 3 Glomerular filtration: Water and solutes smaller than proteins are forced through the capillary walls and pores of the glomerular capsule into the renal tubule. Tubular reabsorption: Water, glucose, amino acids, and needed ions are transported out of the filtrate into the tubule cells and then enter the capillary blood. Tubular secretion: H+, K+, creatinine, and drugs are removed from the peritubular blood and secreted by the tubule cells into the filtrate. © 2015 Pearson Education, Inc. GLOMERULAR FILTRATION a nonselective passive process Driven Low by arterial pressure BP can cause filtration to slow/cease (oliguria/anuria) The glomerulus is a filter: produces the filtrate Includes water and solutes smaller than proteins Proteins and blood cells are too large collects in the glomerular capsule leaves via the renal tubule © 2015 Pearson Education, Inc. TUBULAR REABSORPTION peritubular capillaries reabsorb useful substances: Mostly an active transport process; highly selective Water Glucose Amino acids Ions Membrane carriers exist for only specific needed molecules occurs in the proximal convoluted tubule FIGURE 15.5 SITES OF FILTRATION, REABSORPTION, AND SECRETION IN A NEPHRON. Proximal tubule Distal tubule Glomerular Glucose and HCO3− capsule NaCl H2O amino acids NaCl Blood Some drugs and poisons Filtrate H2O Salts (NaCl, etc.) HCO3− (bicarbonate) H+ Urea Glucose; amino acids Some drugs Reabsorption Active transport Passive transport Secretion (active transport) K+ and some drugs H+ Cortex Collecting duct Medulla H2O Nephron loop NaCl NaCl H2O K+ NaCl Urea H2O Urine (to renal pelvis) © 2015 Pearson Education, Inc. FILTRATE = WASTE PRODUCTS Nitrogenous Waste: Urea—end product of protein breakdown by liver Uric acid—results from nucleic acid breakdown Creatinine—results from direct phosphorylation (creatine metabolism in muscles) Ions: amount/type varies with changes in pH © 2015 Pearson Education, Inc. TUBULAR SECRETION Cells of the tubules secrete excess molecules Eliminates substances not already in the filtrate drugs and excess ions Maintains acid-base balance of blood Tubule cells may secrete H⁺ ions; excess K⁺ Secreted out of the peritubular capillaries into the renal tubule FIGURE 15.5 SITES OF FILTRATION, REABSORPTION, AND SECRETION IN A NEPHRON. Proximal tubule Glomerular HCO3− Glucose and capsule NaCl H2O amino acids Distal tubule NaCl Blood Some drugs and poisons Filtrate H2O Salts (NaCl, etc.) HCO3− (bicarbonate) H+ Urea Glucose; amino acids Some drugs Reabsorption Active transport Passive transport Secretion (active transport) All part of the Renal Tubule K+ and some drugs H+ Cortex Collecting duct Medulla H2O Nephron loop NaCl NaCl H2O K+ NaCl Urea H2O Urine (to renal pelvis) © 2015 Pearson Education, Inc. CHARACTERISTICS OF URINE On average, 1.0 to 1.8 liters of urine/day Urine and filtrate are different Filtrate Not Urine still undergoes reabsorption all components of filtrate will be eliminated is what remains nitrogenous wastes and substances that are not needed © 2015 Pearson Education, Inc. CHARACTERISTICS OF URINE Yellow color due to: the pigment urochrome (from hemoglobin breakdown) eliminated solutes Water consumption influences color: Dilute urine is a pale, straw color Sterile Nasty smell (when left standing) due to bacteria Normal pH of around 6 (slightly acidic) © 2015 Pearson Education, Inc. CHARACTERISTICS OF URINE Solutes normally found in urine Excess sodium and potassium ions Urea, uric acid, creatinine Ammonia Bicarbonate ions (buffer)
