INTORDUCTION & EVOLUTION:
Class of Chordates.
The word amphibian means both sides of life.
(amphi= both bians=life)
The amphibian begins its life in the water and then
finishes it mainly on land.
The change of an animal in its appearance from
baby to adult is called metamorphosis.
An amphibian goes through metamorphosis as it
grows from a baby to an adult.
“The amphibian, because it must be moist,
sometimes hides out in the summer as if
hibernating. This is called estivation.”
-In the Devonian period of palaeozoic era they
were originated from fishes
-In the carboniferous period, they increased their
number, hence that period is called ‘Age of
According to Romer Dipnoi fishes are the “uncles
of Amphibians” According to Newman “Dipnoi and
amphibians had same grand father.”
GENERAL CHARACTERS OF AMPHIBIANS:
Amphibians are cold blooded vertebrates.
Amphibians show four limbs with which they can
swim in water and jump or walk on the land.
In Amphibians animals’ exoskeleton is absent.
Amphibians the adult animals lungs are present.
But in some the gills are present.
Amphibians Skin is a respiratory organ.
The Amphibians skull is dicondylic.
Amphibians Ribs are absent.
In Amphibians The body divisible into head and
trunk Tail is present in, urodela animals.
Amphibians Digestive system is well developed. A
well developed liver is present.
External ear is absent. Middle and inner ears are
present, the middle ear is present.
Amphibians Heart is 3 chambered with 2 auricles
and 1 ventricle.
Blood vascular system contain hepatic and renal
Central nervous system is well developed. 10 pairs
of cranial nerves will arise.
Sexes are separate.
Most frog larvae are herbivores, where as
salamander larvae are carnivores. However, adult
frogs and salamanders are predators and feed on
Parts of the digestive system of a amphibians
After an amphibians eats, the food flows from its
mouth to its esophagus to its stomach.
Digestion begins in the stomach of an amphibian.
Food then moves to the small intestine, where
enzymes from the pancreas start the digestion
From the small intestine, nutrients from the food are
absorbed into the bloodstream and delivered to
Food moves from the small intestine to the large
intestine before waste is eliminated.
Digestive waste enters the cloaca before it exits the
Absorption unabsorbed nutrients and reabsorption of
water takes place in the large intestine.
Liquid wastes are in frog is passed to the urinary
bladder, while solids are routed to the cloaca.
Both liquid and solid wastes in frog are expelled out
through cloaca which is a slit that opens out finally in
digestive system of a frog.
The digestive system of amphibians consists of
digestive tract .
The accessory organs which help to process the food
consumed into small molecules (nutrients) which then
can be easily absorbed and then utilized by the cells of
Not vastly different from humans.
It involves the alimentary canal and the kidney.
In fact the first sustained evidence for ultrafiltration in the
kidney was produced by studying the kidney of frogs.
The kidney's of an amphibian filter waste out of the
Very Important System in order to expell waste materials
as if they remain in body they can cause serious
The Urine travels from the kidneys to the tubes
which are called ureters.
From the ureters the urine travels into the cloaca.
Next the urine can be passed outside the body or
the urine may be stored temporarily in a urinary
bladder just above the cloaca.
Bile is excreted into the digestive system similar to
Solid wastes pass from the large intestine into the
Both solid and liquid waste material is discharged
from the cloaca and the cloacal vent.
Amphibians can get oxygen into their bodies in three
Both the lungs and the skin serve as primary respiratory
organs in amphibians.
“The skin of these animals is highly vascularized and
moist, with moisture maintained via secretion
of mucus from specialized cells.”
“lungs are of primary importance to breathing control
and oxygen exchange.”
Through the nostrills they breathe the air in side.
The air than travels into trachea.
After trachea the air reaches to bronchi
Through bronchi the air reaches finally into lungs
In the lungs the air enters the alveoli where oxygen
and carbon dioxide is exchanged.
Similarly skin also exchanges gasses directly when
it comes in contact with water the water enters the
body with attached oxygen and skin then in turn
releases carbon dioxide.
RESPIRATION THROUGH GILLS:
Many amphibians have gills, at least when they're
Gills are made up of very thin blood vessels,
surrounded by water channels.
When water flows through the gills, the oxygen it
contains crosses the very thin blood vessel walls,
and into the blood.
Amphibians have a tadpole stage and an adult stage,
and the circulatory systems of the two are distinct.
In the juvenile (or tadpole) stage, the circulation is
similar to that of a fish.
In Tadpole Stage:
“The two-chambered heart pumps the blood through the
gills where it is oxygenated, around the body and back
to the heart in a single loop.”
In Adult Stage:
“. In the adult stage, amphibians (especially frogs) lose
their gills and develop lungs. They have a heart that
consists of a single ventricle and two atria. When the
ventricle starts contracting, deoxygenated blood is
pumped through the pulmonary artery to the lungs.
Continued contraction then pumps oxygenated blood
around the rest of the body”
Both male and female frogs have internal sex organs.
-The male frog's foreleg muscles and first fingers swell.
-The reproductive system of the male frog includes two bean-
shaped white or yellowish testes located near the kidneys.
-Sperm cells develop in the testes and pass through tubes to
the kidneys and urinary ducts.
-Female frogs a pair of large, lobed ovaries containing thou-
sands of tiny immature eggs lie near the kidneys.
-During the breeding season eggs enlarge, mature, and burst
through the thin ovarian walls into the body cavity. ---They
remain in structures called ovisacs until ovulation is complete
and then leave the body through the cloacae opening .
FERTILIZATION OF ZYGOTE:
When a frog reproduces, the female frog releases
as many as 200 eggs.
The male sperms can the fertilize the eggs. The
eggs of a frog do not have a shell and usually try
out if they are not kept moist.
Because of this the eggs attach to underwater
plants using a transparent jelly that incases the
This also makes it harder for predators to reach the
eggs. So fertilization takes place in water and new
amphibians are born from the zygote.