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

2. Urine Formation The result of three processes: Glomerular filtration
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Urine Formation
The result of three processes:
Glomerular filtration
Tubular reabsorption
Tubular secretion

3. 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

4. Glomerular Filtration
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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

5. © 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 primarily in the proximal convoluted tubule

6. 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)

7. Filtrate = waste products
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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

8. Tubular Secretion Cells of the tubules secrete excess molecules
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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

9. 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)

10. Characteristics of Urine
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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

11. Characteristics of Urine
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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)

12. Characteristics of Urine
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Characteristics of Urine
Solutes normally found in urine
Excess sodium and potassium ions
Urea, uric acid, creatinine
Ammonia
Bicarbonate ions (buffer)