Introduction to the Amphibian Body

Characteristics of Amphibians

• Amphibians consists of frogs, salamanders, newts, and caecilians

• Amphibians share five key characteristics– 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:

• 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 oxygen-poor 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