Urine Formation pages 516-519 The Urinary System: Urine Formation pages 516-519

Urine Formation The result of three processes: Glomerular filtration © 2015 Pearson Education, Inc. Urine Formation The result of three processes: Glomerular filtration Tubular reabsorption Tubular secretion

Glomerular capillaries Figure 15.4 The kidney depicted schematically as a single large, uncoiled nephron. Afferent arteriole Glomerular capillaries Efferent arteriole Cortical radiate artery Glomerular capsule Three major renal processes: 1 Rest of renal tubule containing filtrate 1 Glomerular filtration: Water and solutes smaller than proteins are forced through the capillary walls and pores of the glomerular capsule into the renal tubule. Peritubular capillary 2 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. 2 3 To cortical radiate vein 3 Tubular secretion: H+, K+, creatinine, and drugs are removed from the peritubular blood and secreted by the tubule cells into the filtrate. Urine

Glomerular Filtration © 2015 Pearson Education, Inc. Glomerular Filtration a nonselective passive process Driven by arterial pressure Low 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: Water Glucose Amino acids Ions Mostly an active transport process; highly selective Membrane carriers exist for only specific needed molecules occurs in the proximal convoluted tubule

Proximal tubule Distal tubule Glomerular capsule HCO3− Figure 15.5 Sites of filtration, reabsorption, and secretion in a nephron. Proximal tubule Distal tubule Glomerular capsule HCO3− Glucose and amino acids NaCl NaCl H2O Blood Some drugs and poisons H+ K+ and some drugs Collecting duct Filtrate Cortex H2O Salts (NaCl, etc.) HCO3− (bicarbonate) H+ Urea Glucose; amino acids Some drugs Medulla H2O Nephron loop NaCl NaCl H2O Reabsorption K+ Active transport Passive transport Urea Secretion NaCl H2O (active transport) Urine (to renal pelvis)

Filtrate = waste products © 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

Tubular Secretion Cells of the tubules secrete excess molecules © 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

All part of the Renal Tubule Figure 15.5 Sites of filtration, reabsorption, and secretion in a nephron. Proximal tubule Distal tubule Glomerular capsule HCO3− Glucose and amino acids NaCl NaCl H2O Blood Some drugs and poisons H+ K+ and some drugs Collecting duct Filtrate Cortex H2O Salts (NaCl, etc.) HCO3− (bicarbonate) H+ Urea Glucose; amino acids Some drugs Medulla H2O Nephron loop NaCl NaCl H2O Reabsorption K+ Active transport Passive transport Urea Secretion NaCl H2O (active transport) All part of the Renal Tubule Urine (to renal pelvis)

Characteristics of Urine © 2015 Pearson Education, Inc. Characteristics of Urine On average, 1.0 to 1.8 liters of urine/day Urine and filtrate are different Filtrate still undergoes reabsorption Not all components of filtrate will be eliminated Urine is what remains nitrogenous wastes and substances that are not needed

Characteristics of Urine © 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)

Characteristics of Urine © 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)