1. Introduction to the Amphibian Body

2. 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

3. 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

4. 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

5. 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

6. 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

7. Amphibian Eyes
The eyes of amphibians are covered by transparent, movable membranes called a nictitating membrane

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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

15. 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

16. 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

17. 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

18. 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

19. 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