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Sponges: |
The main opening of a
sponge is used as an exit to repel waste. |
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Hydra/Polyp (cnidarians): |
The main opening of
cnidarians serves as mouth and anus. |
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Flatworm/Tapeworm (Planarians):
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Because planarians live
in fresh water, which tends to enter the body by osmosis, they have an
excretory organ that largely rids the body of excess water. The organ consists of a
series of interconnecting canals, which run the length of body on each side. The beating of cilia in
flame cells (so named because the beating of cilia reminded some early
investigators of flickering of a flame) keeps the water moving toward the
excretory pores. |
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Roundworm:
|
Circulatory and excretory
food digested in gut is not distributed by any specialised vascular system.
Nutrients and waste are distributed in body cavity whose contents are
regulated by one celled glands (in simple species) or excretory canal along
each side of the body. |
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Molluscs |
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Clam (Bivalve):
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There are two excretory
kidneys in clam, which lie just below the heart and remove waste from the
pericardial cavity for excretion into the mantle cavity. The clam excretes
ammonia, a poisonous substance that requires the concomitant excretion of
water. Land dwelling animals tend to excrete a less toxic substance in a more
concentrated form. |
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Snail (Gastropod):
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There are 2 kidneys or
nephridia in only the primitive gastropods such as archea gastropods while in
advanced forms one kidney is small or lost. The kidney plays
different roles, depending upon the environment in which snail lives. Usually the posterior
chamber excretes uric acid and purines, while the anterior chamber has
osmoregulatory function. Snails living on land
are uricotelic, this means that to preserve water they excrete almost solid
uric acid. Snails living in water
excrete ammonia and are not uricotelic. The renal aperture
(urine opening) is situated in upper region of right mantle cavity. The urine
produced by kidneys is expelled here. Terrestrial gastropods
reduce water loss by sealing the mantle cavity with an extended mantle
collar. |
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Octopus (Cephalopod):
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Excretory functions are
carried out by nephridia (kidneys), tubular structures that collect fluid
from the coelom and exchange salts and other substances with body tissues as
fluid passes along the tubules for excretion. The nephridia empty
into mantle cavity. |
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Annelids (Earthworm):
|
The excretory system
consists of paired nephridia or coiled tubules in each segment. Nephridia have 2 openings:
one is a ciliated funnel that collects coelomic fluid and the other is an
exit in the body wall. Between the 2 openings
is a convoluted region where waste material is removed from the blood vessels
about the nephridium. |
|
Arthropods (Insect):
|
Terrestrial forms have
an excretory system that conserves water. The malphigian tubules
collect wastes from the blood and reabsorb water so that only dry material is
excreted. Marine crustaceans such
as gry fish have excretory system consisting of a pair of green glands lying
in the head region anterior to the oesophagus. Each organ possesses a
glandular region for waste removal, a bladder and a duct that opens ventrally
at base of the antennae. |
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Echinoderms (Starfish):
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Star fish has no
excretory organs. |
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Chordates:
|
The kidneys are
important excretory and water regulating organs that conserve or rid the body
of water as appropriate. |
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Fishes:
|
The kidney filters
liquid waste materials from the body, these wastes are then passed out of the
body. The kidney is also
extremely important in regulating water and salt concentration within the
fish’s body, allowing certain fish species to exist in freshwater or salt
water and in some cases both. The vent is the
external opening to digestive, urinary and reproductive tracts. In most fish
it is immediately in front of anal fin. Ammonia is formed
immediately after the amino group is removed from protein. This process
requires very little energy. Ammonia is highly soluble in water but very
toxic. Aquatic animals such as
bony fishes, aquatic invertebrates and amphibians excrete ammonia because it
is easily eliminated in the water. |
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Amphibians:
|
Liquid wastes from
kidney travel by way of ureters to the urinary bladder. Solid wastes from the
large intestine pass into the cloaca. Both liquid and solid
waste materials leave the body by way of the cloaca and the cloacal vent. Terrestrial amphibians
and mammals excrete nitrogenous wastes in the form of urea because it is less
toxic than ammonia and can be moderately concentrated to conserve water. Urea is produced in the
liver by a process that requires more energy to produce than ammonia does. |
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Reptiles:
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The metanephric kidneys
of reptiles are lobulated. One or more renal arteries can be presented to
receive blood from the renal portal system. The nitrogenous wastes
of reptiles are in form of ammonia, urea, uric acid or a combination of
these. Crocodilians, snakes
and some lizards do not have a urinary bladder. In chelonians and
lizards with a bladder is connected to the cloaca by a short urethra. Urine passes into the
cloaca and then into the urinary bladder if present or into distal colon
where water resorption occurs. The cloaca typically
consists of 3 chambers – The coprodeum is the
most cranial and receives faecal material and urinary wastes. The uroderm is the
middle section and receives genital secretions and urinary wastes from the
urogenital ducts. The caudal proctoderm
acts as a reservoir for faecal and urinary wastes before they are excreted.
This also is the location of the openings of the musk glands. |
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Birds:
|
Insects, reptiles,
birds and some dogs (Dalmatians) excrete uric acid. Reptiles and birds
eliminate uric acid with their faces. The white material seen
in bird droppings is uric acid. It is not very toxic
and is not very soluble in water. Excretion of wastes in
the form of uric acid conserves water because ti can be produced in a
concentrated form due to its low toxicity. Because it is relatively
insoluble and nontoxic, it can accumulate in eggs without damaging the
embryo. The synthesis of uric
acid requires more energy than urea synthesis. There is no urinary
bladder in birds. |
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Mammals:
|
In mammals, 2 major
excretory processes are the formation of urine in the kidneys and the
formation of faces in the intestine. The waste products are
eliminated by urination and defecation respectively. While urine and faces
are both water material of body processes they are in completely different
categories. Urine is a waste
product of the urinary system process while faces are waste products of
digestive system. Faces may contain
harmful materials such as bacteria, viruses and parasitic worms. Urine on the other
hand, contains excess water, salt and protein waste in the form of urea and
seldom carries any pathogens. |
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Primates: |
The kidney is a major
excretory organ of primates and other vertebrates. The principle
responsibility of the organ is to separate urea, toxins and other types of
waste from the blood, while water; salt and electrolytes are maintained at an
appropriate level. Due to this important
role, the kidney is also involved in blood pressure and acid base regulation
in the body. Nephrons are the basic
filtering units of the kidney, more than a million of them being present in a
normal adult human kidney. Working together, the
nephrons are able to filter blood at an impressive rate, processing the
entire 5 quarter water content of human circulatory system about every 45
minutes. Only a minute portion
of the material passing through the kidneys is actually excreted, however,
the vast majority being reabsorbed by the nephrons. |