ANIMAL EXCRETORY SYSTEM
GRADE 10
OSMOREGULATION
• OSMOREGULATION IS AN IMPORTANT PART OF HOMEOSTASIS.
• OSMOREGULATION IS THE BALANCING OF WATER AND SALTS IN THE BODY.
• THE OSMOREGULATORY SYSTEM IN ANIMALS ALSO REMOVES METABOLIC WASTES IN A
PROCESS CALLED EXCRETION.
The breakdown of
proteins, amino acids
and nucleic acids
releases nitrogen and
excess nitrogen must
be excreted.
Amino acids are
broken down to
generate energy or
forms fats or
carbohydrates.
To do this the NH2
must be removed.
NITROGENOUS WASTE PRODUCTS
• THE REMOVAL OF
NITROGEN IS DONE IN THE
FORM OF AMMONIA, UREA
OR URIC ACID.
• THE PRODUCTION OF
AMMONIA, UREA AND URIC
ACID REQUIRE DIFFERENT
AMOUNTS OF WATER AND
ENERGY.
AMMONIA
• NH2 (FROM AMINO ACID) +
H+ = AMMONIA
• THIS REQUIRES VERY LITTLE
ENERGY BUT IS VERY TOXIC SO
NEEDS A LOT OF WATER TO
DILUTE IT AS IT LEAVES THE BODY.
• AMMONIA IS EXCRETED BY FISH
AND AQUATIC ANIMALS WHO
ARE SURROUNDED BY WATER.
UREA
• UREA IS LESS TOXIC THAN AMMONIA SO
CAN BE EXCRETED IN MORE CONCENTRATED
SOLUTIONS.
• THE PRODUCTION OF UREA REQUIRES
ENERGY BUT ALLOWS THE BODY TO SAVE
WATER – THIS IS IMPORTANT FOR
TERRESTRIAL (LAND) MAMMALS.
• 2(NH2)
+
CO2
= UREA
• SHARKS, AMPHIBIANS, MAMMALS
URIC ACID
• URIC ACID IS FORMED BY A COMPLEX SERIES OF
ENZYMATIC REACTIONS.
• IT REQUIRES A LOT OF ENERGY TO MAKE URIC ACID.
• IT IS NOT VERY TOXIC SO CAN BE VERY CONCENTRATED.
• IT IS NOT VERY WATER SOLUBLE – IT IS GOOD WHEN
WATER IS IN SHORT SUPPLY.
• INSECTS, REPTILES, BIRDS.
• IN REPTILES AND BIRDS, URIC ACID GOES FROM THE
KIDNEYS TO THE CLOACA – HERE WASTE FROM KIDNEYS,
DIGESTIVE AND REPRODUCTIVE SYSTEMS COMBINE.
• THEY ARE REFLUXED INTO THE INTESTINE WHERE WATER IS
RE-ABSORBED.
• THE WHITE PART OF BIRD FAECES IS URIC ACID.
• URIC ACID IS EASY TO STORE INSIDE BIRD AND REPTILE
EGGS AS IT IS NON-TOXIC AND CONCENTRATED.
• HUMANS CAN PRODUCE URIC ACID FROM PURINE AND
PYRIMIDINE NUCLEIC ACID BUT IN SOME PEOPLE IT CAUSES
GOUT (JOINT PAIN).
EXCRETORY ORGANS IN INVERTEBRATES
• INVERTEBRATES HAVE TUBULAR EXCRETORY ORGANS FOR
OSMOREGULATION.
• PLANARIANS (FLATWORMS) HAVE 2 STRANDS OF
BRANCHING TUBULES THAT RELEASE WASTE THROUGH
EXCRETORY PORES.
• EACH STRAND HAS A NUMBER OF FLAME CELLS THAT
HAVE BEATING CILIA THAT PUSH/PROPEL EXCESS WATER
AND WASTE TO THE PORES.
• EARTHWORMS ARE DIVIDED
INTO SEGMENTS – EACH
SEGMENT HAS A PAIR OF
NEPHRIDIA (EXCRETORY
STRUCTURES).
• EACH NEPHRIDIUM IS A TUBULE
WITH A CILIATED OPENING AND
AN EXCRETORY PORE.
• AS FLUID FROM THE COELOM
MOVES THROUGH THE TUBULE
NUTRIENTS ARE ABSORBED BY
CAPILLARIES (SMALL VEINS).
• URINE (WATER, WASTES, SALTS)
IS PASSED OUT THROUGH THE
EXCRETORY PORES.
• EARTHWORMS EXCRETE A VERY
DILUTE URINE – THEY PRODUCE
A VOLUME OF URINE EQUAL TO
60% OF THEIR BODY WEIGHT.
INSECTS
• INSECTS HAVE A LONG MALPIGHIAN
TUBULE ATTACHED TO THE GUT.
• URIC ACID IS ACTIVELY TRANSPORTED
FROM HEMOLYMPH.
• WATER FOLLOWS A SALT GRADIENT
ESTABLISHED BY THE ACTIVE
TRANSPORT OF K+.
• WATER AND NUTRIENTS ARE REABSORBED BY THE RECTUM.
• URIC ACID IS EXPELLED VIA THE ANUS.
ARTHROPODS
(EXOSKELETON)
• IN AQUATIC ARTHROPODS, NITROGENOUS WASTE
IS REMOVED BY DIFFUSION ACROSS THE GILLS.
• SOME CRUSTACEANS (SHELL FISH) HAVE AN
ORGAN CALLED THE GREEN GLANDS WHERE FLUID
COLLECTS IN THE VENTRAL PORTION OF THE HEAD
REGION.
• IN SHRIMPS AND PILLBUGS THE EXCRETORY ORGANS ARE IN THE MAXILLARY SEGMENT AND
ARE CALLED MAXILLARY GLANDS.
• SPIDERS AND OTHER ARACHNIDS HAVE A COXAL GLAND WHICH ARE USED FOR EXCRETION.