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Amphibians Introduction to Frog Dissection Evolution of Amphibians “Amphibian” comes from the Greek meaning “double life”. Spends part of its life in water and part on land Evolved about 370 million years ago from lobe-finned bony fish Amphibian Adaptations to Land Lungs: to breath air Stronger limb bones: hold its weight and allow for efficient movement Skin: mucus is secreted by glands in the skin to help protect it from drying out Characteristics of Amphibians Ectothermic (cold-blooded): body temperature varies with its environment’s temperature Lives in water as a larva and on land as an adult Moist, thin skin with no scales Feet- lack claws and often are webbed Most use gills, lungs, and skin in respiration Eggs without shells or multicellular membranes Classification of Amphibians The class Amphibia consists of 3 orders: Anura (“tailless”): frogs and toads Urodela ( “visible tail”): salamanders Apoda (“without feet”): caecilians Frog’s Skin A frog’s skin serves two important functions: Respiration (breathing): gas exchange of oxygen & carbon dioxide Skin is permeable to the gases Respiration occurs through skin when frog is underwater Protection: some glands secrete foul-tasting or poisonous substances that protect the frog from enemies Sense Organs Nictitating membrane- transparent membrane that protect the eye and keeps it moist Tympanic membrane- eardrum Frog’s mouth Internal nares (nostrils) Eustachain tube- tubes lead to the ears Maxillary teeth: line the perimeter of the upper jaw Vomerine teeth: 2 teeth found in the middle of the roof of the mouth Pharynx (throat) Glottis- slit through which air passes in and out of the trachae (short tube that goes to the lungs) Esophagus: tube into which food is swallowed; leads to the stomach Mouth Cavity Vomerine Teeth Internal Nares Maxillary Teeth Entrance to Esophagus Glottis Tongue Frog’s Digestive System Stomach- secretes gastric juices that help break down food Small Intestine- digestion is completed and nutrients pass through capillary walls into the bloodstream Liver- produces bile which is needed for the digestion of fat Gallbladder- stores bile Pancreas- secretes enzymes that enter the small intestine and help break down food Large intestine- collects indigestible waste and pushed into the cloaca Cloaca- muscular cavity at end of large intestine through which digestive wastes, urine, and eggs or sperm leave the body Frog’s Circulatory System Consists of the heart and blood vessels Frogs have a 3 chambered heart: 2 receiving chambers (atria) Right atrium and left atrium One sending chamber (ventricle) Blood vessels: Veins- carry blood to the heart Arteries- carry blood away from the heart Liver Heart, Liver Atria Ventricle Frog’s Respiratory System In addition to their skin: Larval frogs respire via their gills Adults lose the gills during and respire via their lungs Frog’s Excretory System The urinary system consists of the frog’s kidneys, ureters, bladder, and cloaca. Kidneys: excretes urine Ureter: a tube connected to each kidney that carries urine from kidney to the urinary bladder Urinary bladder: a sac that stores urine until it passes out of the body through the cloaca. Frog’s Reproductive System In males, two bean-shaped testes (produce sperm) located near the kidneys In females, two ovaries (produce eggs) located near the kidneys Both sperms and eggs exit via the cloaca