Introduction to the Amphibian Body

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