Introduction to the Amphibian
Body
Characteristics of Amphibians
• Amphibians consists of frogs, salamanders, newts,
and caecilians
• Amphibians share five key characteristics
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1. Legs
2. Lungs
3. Double-loop Circulation
4. A partially divided heart
5. Cutaneous respiration
• These characteristics allow amphibians to thrive
on land
Characteristics of Amphibians
• Amphibian eggs are not watertight, and
therefore amphibians need to reproduce in a
wet area
• Because amphibians need a wet area to
reproduce many amphibians must live in a
moist environment
Movement and Response
• Many challenges that amphibians face involve
having to move on land
• Not all of amphibian’s sense organs work as
well in air as in water
– Example: larval amphibians have a lateral line that
they use to detect movement of the water, but
they usually lose their lateral line by adulthood
Amphibian Skeleton
• Terrestrial vertebrates must rely on the
support of their strong internal
skeleton
• Strong limbs of the skeleton help
support the body’s weight and allows
movement
• Frog skeletons have several
specializations for jumping and landing
– The bones of the lower limbs are fused into
a single, thick bone
– The hips also have thick bones with a
sturdy structure that absorbs the impact of
landing
Sense Organs
• The sense of sight and hearing are well
developed in most amphibians
• The primary sense organs of amphibians are
the eyes and ears
Amphibian Eyes
• The eyes of amphibians are covered by
transparent, movable membranes called a
nictitating membrane
Amphibian Ears
• The inner ear detects sound
• Sounds are transmitted to the inner
ear by the tympanic membrane, or
eardrum, and a small bone that
extends between the tympanic
membrane and the inner ear
• Sound first strikes the tympanic
membrane
– The tympanic membrane is located on
the side of the head
– Vibrations cause small movements that
are transmitted to the fluid-filled inner
ear
– In the inner ear, sensitive hair cells
change sound vibrations to nervous
impulses
– These impulses are then transmitted to
the brain
Respiration
• One of the biggest challenges faced by
amphibians when they leave the water is
gathering oxygen from the air
• In amphibians the following structures work
together to ensure that sufficient oxygen
reaches the body tissues:
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Skin
Lungs
Double-loop circulation
Partially divided heart
Amphibian Lungs
• Adult amphibians breathe
with lungs
– A lung is an internal,
baglike organ that allows
oxygen and carbon dioxide
to be exchanged between
the air and bloodstream
• The amount of oxygen a
lung can absorb depends
on the internal surface
– The greater the surface
area is, the greater amount
of oxygen that can be
absorbed
How amphibians breathe
• Amphibians breathe by changing the volume and
pressure of air in its mouth while either opening
or closing its nostrils
• With each breath oxygen is drawn into the lungs
• In the lungs oxygen mixes with a small amount of
air that has already given up most of its oxygen
– Due to the mixing the efficiency of lungs is much less
than that of gills
– This is okay though because air contains 20x as much
oxygen as sea water
Amphibian Skin
• Amphibians can obtain oxygen
through their thin, moist skin =
cutaneous respiration
• In cutaneous respiration, gases
and water pass directly
through the skin
– Skin must be moist for
cutaneous respiration to work
– To keep skin moist amphibians
have mucous glands
Amphibian Circulation
• The tissues of land animals require greater
amounts of oxygen
• The structure of the amphibian circulatory
system, which includes a partially divided
heart and double-loop circulation, allows
oxygen to be delivered to the body in an
efficient manner
Amphibian Partially Divided Heart
• The top chambers of the
amphibian heart are
divided into left and right
sides by the wall called
the septum
• The heart’s bottom
chamber is not divided
– This allows a mixture of
oxygen-rich and oxygenpoor blood to be delivered
to the amphibian’s tissues
Blood Flow in the Amphibian Heart
• 1. Oxygen-poor blood from
the body enters the right
atrium
• 2. The pulmonary veins
carry oxygen-rich blood
from the lungs to the left
atrium
• 3. A mixture of oxygen-rich
and oxygen-poor blood
enters the ventricle
• 4. The ventricle pumps
blood to the lungs and
body tissues
The Spiral Valve
• Some amphibians have a spiral valve that
divides the conus arteriosus
• The spiral valve helps keep the two streams of
blood separate as they leave the heart
Double-Loop Circulation
• Amphibians evolved to have a
second circulatory loop
• The evolution of the second
circulatory loop allows more
oxygen to be delivered to their
bodies
• In the circulatory loop that
connects an amphibian’s heart
to its lungs there are blood
vessels called pulmonary veins
– Pulmonary veins are the vessels
that carry the oxygen-rich blood
from the amphibian’s lungs
directly back to its heart
Double-Loop Circulation
• The amphibian’s second
circulatory loop carries the
oxygen-rich blood from the
heart to the body
• The advantage:
Amphibians can pump
oxygen-rich blood to the
amphibian’s tissues at a
much higher pressure and
speed than that of fishes
Review Questions:
• Describe the key characteristics shared by all
amphibians
• Identify the function of the tympanic
membrane
• Summarize how amphibians take in oxygen
• Contrast the single-loop circulation o fishes
with the double-loop circulation of
amphibians