Transcript Ch 15 Urine Formation

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)
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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)