Biology
Sylvia S. Mader
Michael Windelspecht
Chapter 36
Body Fluid Regulation
and Excretory
Systems
Lecture Outline
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Outline
• 36.1 Animal Excretory Systems
• 36.2 The Human Urinary System
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36.1 Animal Excretory Systems
• Osmoregulation
 Balancing the levels of water and salts in the body
• Excretion
 The osmoregulatory system of an animal that functions to
remove metabolic wastes from the body.
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Animal Excretory Systems
• The breakdown of amino acids and nucleic acids
results in ammonia
 High solubility permits it to be excreted directly by
many aquatic animals
 Terrestrial animals must convert ammonia to urea or
uric acid because ammonia is very toxic
• Urea can be excreted in a moderately concentrated solution
– Mammals, sharks, and adult amphibians
• Uric acid requires much less water per unit of nitrogen
excreted
– Reptiles, birds, and insects
– Requires more energy to produce than urea
– Allows invasion of drier habitats far from standing water
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Nitrogenous Wastes
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proteins
amino acids
NH2
most fishes and
other aquatic
animals
adult amphibians,
sharks, and
mammals
Insects, birds, and
reptiles
ammonia
urea
uric acid
O
H
N
O
H
H2N
C
HN
NH2
C
H
C N
C
O
C
H
O
C N
N
H
H
water needed to excrete
energy needed to produce
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Animal Excretory Systems
• Excretory Organs Among Invertebrates
 Most animals have tubular excretory organs
• Regulate the water-salt balance of the body
• Excrete metabolic wastes into the environment
– Flame cells in planarians
– Nephridia in earthworms
– Malpighian tubules in insects
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Excretory Organs in Animals
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flame cell
excretory tubule
fluid filtering
into flame cell
flame cell
nucleus
cilia
excretory
pore
excretory
tubule
a.
Flame-cell excretory system in planarians
capillary network
tubule
bladder
septum
entrance of
nephridiostome
pore
b.
Earthworm nephridium
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Animal Excretory Systems
• Osmoregulation by Aquatic Vertebrates
 An excretory system regulates blood ion
concentrations
 Dependent upon concentration of mineral ions such
as sodium and potassium
 The concentration of urine produced by an animal
varies depending on its environment, as well as water
and salt intake
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Animal Excretory Systems
• Water tends to move into the region with the
lowest water concentration
 A marine environment
•
•
•
•
High in dissolved salts
Tends to promote the osmotic loss of water, and
The gain of ions by drinking water
Cartilaginous fishes have blood nearly isotonic to seawater
– Blood contains enough urea to match the tonicity of sea water
 Fresh water environment
• Tends to promote a gain of water by osmosis, and
• A loss of ions as excess water is excreted
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Animal Excretory Systems
• Bony Fishes
 Marine bony fishes
•
•
•
•
Blood plasma is hypotonic to sea water
Passively lose water through gills
Must constantly drink seawater to compensate
Excess salt ions actively transported back into seawater
through the gills
 Freshwater bony fishes have the opposite problem
• Blood plasma is hypertonic to fresh water
• Passively gain water through gills
• Eliminate excess water through copious hypotonic urine
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Body Fluid Regulation in Bony
Fishes
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passive loss
of water
through
gills
drinks seawater
salts actively
excreted by gills
scanty amount
of isotonic
urine contains
some salts
a. Marine bony fish
passive gain of
water through gills
does not drink
salts actively
taken up by gills
b. Freshwater bony fish
large amounts of hypotonic
urine contain few salts
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Animal Excretory Systems
• Osmoregulation by Terrestrial Vertebrates
 Terrestrial animals lose water through
excretion and respiration
 Must drink water to make up for loss
• Some reduce excretory loss by excreting nitrogen
as relatively insoluble uric acid
• Certain animals, like the kangaroo rat, also have a
highly convoluted nasal passage with a mucous
membrane surface that excretes salt
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Adaptations of a Kangaroo Rat
to a Dry Environment
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Exhaled air is
cooled and dried
in long convoluted
air passages.
Animal fur prevents
evaporative loss of
water at skin.
Urine is the
most hypertonic
known among
animals.
Fecal pellets
are dry.
Oxidation of
food results in
metabolic water.
© Bob Calhoun/Bruce Coleman, Inc.
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Animal Excretory Systems
• Osmoregulation by Terrestrial Vertebrates
 Birds, Reptiles, and Mammals
• Kidneys efficient in water conservation
• Some have specialized salt glands that function to
actively transport salt from the blood to the
external environment
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Adaptations of Marine Birds to a
High Salt Environment
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salt solution
exits here
salt solution
runs down
beak here
© Eric Hosking/Photo Researchers, Inc.
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36.2 The Human Urinary
System
• Human kidneys
 Located on either side of vertebral column,
just below the diaphragm
• Each is connected to a ureter
• Ureters conduct urine from the kidneys to the
urinary bladder
• Urinary bladder
 Stores urine
 Urine voided through urethra
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The Human Urinary System
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
renal artery
1. Kidneys produce
urine.
renal vein
aorta
inferior vena cava
2. Ureters transport
urine.
3. Urinary bladder
stores urine.
4. Urethra passes
urine to outside.
a.
b.
© James Cavallini/Photo Researchers, Inc.
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The Human Urinary System
• Kidneys
 Composed of three major parts:
• Renal cortex
– Outer region
– Granular appearance
• Renal medulla
– Cone-shaped renal pyramids
• Renal pelvis
– Hollow-chambered innermost part of the kidney
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Macroscopic & Microscopic
Anatomy of the Kidney
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nephrons
renal
pelvis
renal
cortex
renal
medulla
collecting
duct
ureter
renal artery
and vein
a. Gross anatomy
renal pyramid
in renal medulla
renal
pelvis
b. Two nephrons
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The Human Urinary System
• Nephrons
 Each kidney is composed of many tubular
nephrons that produce urine
 Each nephron is composed of several parts
•
•
•
•
•
•
Glomerular capsule (Bowman’s capsule)
Glomerulus
Proximal convoluted tubule
Loop of the nephron (loop of Henle)
Distal convoluted tubule
Collecting duct
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Nephron Anatomy
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Renal Cortex
glomerular capsule
(Bowman's capsule)
proximal
convoluted
tubule
distal
convoluted
tubule
glomerulus
efferent
arteriole
afferent arteriole
venule
renal
artery
renal vein
peritubular
capillary
network
collecting duct
Loop of the nephron (loop of Henle)
descending limb
ascending limb
Renal Medulla
a. A nephron and its blood supply
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Nephron Anatomy
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peritubular capillary
efferent arteriole
afferent arteriole
glomerulus
b. Surface view of glomerulus and its blood supply
distal
convoluted tubule
proximal
convoluted tubule
glomerular
capsule
c. Cross section of glomerulus and convoluted tubules
50X
ascending limb
descending limb
collecting duct
capillaries
d. Cross sections of a loop of nephron limbs and
collecting duct. (The other cross sections are
those of capillaries.)
b: © Science Photo Library/Getty RF; (c, d): © Ed Reschke/Peter Arnold/Photolibrary
100X
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The Human Urinary System
• Urine Formation
 Urine production requires three distinct processes:
• Glomerular filtration in glomerular capsule
– Blood pressure causes small molecules to move from the
glomerulus to the inside of the glomerular capsule
– The composition of the glomerular filtrate the same as the
composition of plasma, except the filtrate is protein-free
• Tubular reabsorption at the convoluted tubules
– Active transport of Na+ ions
– Cl- ions and water follow passively
– Nutrients are selectively reabsorbed
• Tubular secretion at the convoluted tubules
– Certain molecules (e.g., H+ and penicillin) are actively secreted
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into the convoluted tubules
Processes in Urine Formation
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
peritubular
capillary
Glomerular Filtration
proximal
Water, salts, nutrient
convoluted
molecules, and waste
glomerular capsule
tubule cell
molecules move from
microvilli
the glomerulus to the
H2 O
inside of the glomerular
lumen
urea
capsule. These small
mitochondrion
molecules are called
glucose
the glomerular filtrate.
nucleus
amino
acids
uric
acid
b.
250X
proximal
convoluted
tubule
salts
Tubular Reabsorption
Nutrient and salt molecules are
actively reabsorbed from the
convoluted tubules into the
peritubular capillary network, and
water flows passively.
glomerulus
efferent
arteriole
Tubular Secretion
Certain molecules (e.g., H+ and
penicillin) are actively secreted
from the peritubular capillary
network into the convoluted
tubules.
afferent
arteriole
distal
convoluted
tubule
renal
artery
renal
vein
venule
collecting
duct
peritubular
capillary
network
loop of the
nephron
H2 O
urea
uric acid
salts
NH4+
creatinine
b: © Joseph F. Gennaro, Jr./Photo Researchers, Inc.
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The Human Urinary System
• The Kidneys and Homeostasis
 The kidneys have four homeostatic functions
•
•
•
•
Excretion of metabolic wastes
Maintenance of water-salt balance
Maintenance of acid-base balance (pH balance)
Secretion of hormones
– Erythropoietin to stimulate red blood cell production
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The Human Urinary System
• Maintaining the Water-Salt Balance
 Excretion of hypertonic urine
• Dependent upon the reabsorption of water from the loop of the
nephron and the collecting duct
• An osmotic gradient within the renal medulla causes water to
leave the descending limb along its entire length
• Filtrate within the collecting duct encounters the same osmotic
gradient
– Antidiuretic hormone (ADH)
» Released by the posterior lobe of the pituitary
» Promotes the reabsorption of water in the collecting duct
» Allows excretion of hypertonic urine
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Reabsorption of Salt and Water
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C1-
Na+
Increasing solute concentration in renal medulla
H2O
Renal
cortex
Outer
medulla
ascending
limb
Na+
H2O
C1-
descending
limb
H2O
Urea
H2O
H2O
Inner
medulla
loop of the
nephron
collecting
duct
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The Human Urinary System
• Hormones Control the Reabsorption of Salt
 The renin-angiotensin-aldosterone system
•
•
•
•
Low blood volume stimulates the kidneys to secrete renin
Renin changes angiotensinogen into angiotensin I
Angiotensin I is converted to angiotensin II
Angiotensin II stimulates the adrenal glands to release
aldosterone
• Aldosterone promotes the secretion of K+ and the reabsorption
of Na+ ions
 Atrial natriuretic hormone (ANH)
• Secreted by the atria of the heart when cardiac cells are
stretched due to increased blood volume
• ANH inhibits the secretion of renin
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The Renin-AngiotensinAldosterone System
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liver
kidneys
adrenal cortex
secrete
renin
blood vessel
stimulates
secretes
secretes
speeds
angiotensin I
angiotensin II
angiotensinogen
aldosterone
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The Human Urinary System
• Maintenance of pH
 pH is regulated by
• The bicarbonate buffer system
– pH adjusted by either
» The reabsorption of the bicarbonate ions, or
» The secretion of hydrogen ions
 Breathing
• Excretion of carbon dioxide by the lungs affects
bicarbonate levels in the blood
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