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Excretory:
Disposal & Osmoregulation
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Excretion: Disposal of nitrogen-containing
wastes
Osmoregulation: Control of gain and loss of
water and solutes
Osmoregulation based largely on
regulating solutes
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Water follows the movement of solutes by
osmosis
Excretion: Aquatic Animals
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Animals must dispose of nitrogenous waste
Metabolism produces nitrogenous wastes from breakdown
of proteins and nucleic acids
Most aquatic animals dispose of their nitrogenous wastes as
ammonia
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Highly soluble in water
Diffuses rapidly across cell membranes
Excretory: Saltwater Fish
Excretion: Land Animals
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Land animals convert ammonia to less toxic
compounds
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Can be safely stored and transported in the body
Released periodically by excretory system
Requires energy for conversion
Different adaptations and type of reproduction determine
excretion as urea or uric acid
Excretory:
Disposal & Osmoregulation
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Urea
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Excreted by mammals, most amphibians, sharks, and
some bony fishes
Can be stored in concentrated solution but requires
water for disposal
Uric acid
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Excreted by birds, reptiles, insects, some amphibians
Excreted as solid paste for water conservation
Uses more energy for excretion
Excretory
Excretory: Waste
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Protein and nucleic acid breakdown nitrogen-containing wastes toxic byproducts of
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Ammonia poisonous but soluble and
easily disposed of
Urea less toxic, easy to store and excrete
Some land animals save water by excreting
a virtually dry waste
Excretory: Waste in Urine
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Urea – from amino acid breakdown
Uric Acid – from nucleic acid breakdown
Creatinine – muscle metabolism waste
product
Excretory System
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The excretory system
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expels wastes
regulates water and salt
balance
Two human kidneys
each contain ~ million
nephrons
Urine leaves kidneys via
ureters
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Stored in urinary bladder
Excretory Systen
Bowman’s capsule
Arteriole
from renal
artery
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Each nephron:
folded tubule
and associated
blood vessels
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Nephrons extract
filtrate from blood
Refine filtrate into
much smaller
amount of urine
1 Proximal tubule
Glomerulus
Capillaries
Arteriole
from glomerulus
Branch of
renal vein
3 Distal
tubule
From
another
nephron
Collecting
duct
2 Loop of Henle
with capillary
network
D. DETAILED STRUCTURE OF A NEPHRON
Figure 25.9D
LE 25-11
Blood
Filtrate composition
H2O
NaCI
HCO3–
H+
Urea
Glucose
Amino acids
Some drugs
Proximal tubule
Bowman’s
capsule Nutrients H2O
HCO3–
NaCI
Some
H+
drugs
and poisons
Distal tubule
NaCI
H2O
HCO3–
K+
H+
Cortex
Collecting
duct
Medulla
Loop of
Henle
NaCI
NaCI
H2O
Reabsorption
Urea
Secretion
NaCI
H2O
Urine (to renal pelvis)
Excretory: Filtration
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Filtration (Bowman’s capsule)
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Blood pressure forces water and many
solutes from blood (glomerulus) into
nephron
Excretory: Reabsorption /
Secretion
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Controlled secretion of H+ and
reabsorption of bicarbonate ions help
regulate blood pH
Secretion also includes active transport
of drugs and poisons
Reabsorption of salts and urea allow
osmotic reabsorption of water
Excretion: Reabsorption /
Secretion
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PROXIMAL TUBULE
– always reabsorb glucose and amino
acid
- sometimes water, sodium, potassium,
calcium depending on need
Secretion
urea, creatinine, ions, drugs and toxins
Excretory: Reabsorbing Water
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LOOP OF HENLE
- much water reabsorbed via active
transport of salt
salt concentration in kidney higher in
medulla
Longer loop – more water conservation
(desert animals)
Excretory:
Reabsorption/Secretion
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DISTAL TUBULE
specialized “Urine fine tuning”
Aldosterone hormone – increases
amount of sodium reabsorbed into
blood (water follows)
Excretory: Water Reabsorption
in Collecting Duct
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Water reabsorbed
ADH (antidiuretic hormone) – cause
collecting walls to be permeable to
water to be reabsorbed
Caffeine interferes with ADH
(dehydration)
Excretory: Regulates Blood
Pressure
Releases RENIN when blood pressure
low
- enzyme that causes production of
chemical (angiotensin II) to constrict
blood vessel
- Angiotensin II increase aldosterone
production
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Excretory: Dialysis
Homeostasis: Liver
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It assists the
kidneys by
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making urea from
ammonia
breaking down toxic
chemicals
Liver
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Blood from intestines flows through the
liver before distribution to the rest of
the body
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Allows liver to adjust blood’s chemical
content