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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)
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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