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Frog Dissection Activity
Introduction to the Frog:
Frogs are amphibians, living both on land and in water. Their anatomy is very unique. Their
bodies are similar to humans in that they have skin, bones, muscles, and organs. The body of
a frog can be divided into a head, a short neck, and a trunk. The head contains the brain,
mouth, eyes, ears and nose. The trunk or abdomen holds all of the frog's internal organs.
Frogs have the same kinds of organs as humans and the same organ systems with a few
differences. For example, frogs have a long, sticky tongue which they use to capture food.
They also have teeth, which unfortunately are very weak and rather useless.
Maxillary teeth
Internal nostrils
Vomerine teeth
Esophagus
Glottis
Tongue
If you closely examine the frog’s mouth, you will find the following: tongue, vomerine teeth,
maxillary teeth, internal nostrils, the glottis opening and the esophagus.
A frog uses its tongue for grabbing prey. The vomerine and maxillary teeth are used for
holding the prey. The internal nostrils are used by the frog for breathing. The glottis is a
tube, which leads to the lungs, while the esophagus is a tube which leads to the frog's
stomach.
The internal structures of a frog include: the heart, the lungs, the kidneys, the stomach, the liver,
the small intestine, the large intestine, the spleen, the pancreas, the gall bladder, the urinary
bladder, the cloaca, the ureter, the oviducts & ovaries (female), the testes (male), and fat bodies.
The one major difference between the anatomy of a frog and that of humans is that the anatomy of a
frog is simpler than the anatomy of a human. Frogs don't have ribs or a diaphragm. Humans have
both and they play an important function in breathing and respiration. Breathing takes oxygen in and
carbon dioxide out of the body. Respiration is the process by which our cells are provided with
oxygen for metabolism and carbon dioxide, which is produced as a waste gas, is removed.
Artery
Esophagus
Right Atrium
Left Atrium
Lung
Ventricle
Stomach
Liver
Gallbaldder
Pancreas
Small Intestine
Cloaca
Large Intestine
The stomach helps the frog break down food and the liver also helps with digestion (it
makes bile). Specialized cells in the liver initiate the formation and secretion of bile. In many
species, bile is stored in the gall bladder between meals. When eating, the bile is
discharged to help with digestion. The first and shortest part of the small intestine is
responsible for the breakdown of food in the small intestine. Most chemical digestion takes
place in the first part of the small intestine. The small intestine also absorbs nutrients
from food. The large intestine absorbs water and collects solid waste. The cloaca is a
storage site, it collects eggs, sperm, urine and feces. The cloaca opening is also where
sperm, eggs, urine, and feces exit the frog's body. The spleen stores blood, while the
kidneys filter the blood. The ureters carry urine from the kidneys to the bladder. The
(urinary) bladder stores urine. The testes make sperm, while the ovaries makes eggs and
the eggs travel through the oviducts.
A frog's skin is always moist. It is made up of two layers, an outer epidermis and an inner
dermis. In addition to protecting the frog, the skin also helps the frog breathe. A frog will
take in oxygen from the water through their skin. The oxygen in the water passes through
their skin and goes directly to their blood. Frogs also have a pair of lungs which allows
them to breathe when on land.
The frog’s heart (which is part of the circulatory system) has three chambers. There are two
atria and one ventricle. There is a valve within the frog's heart that directs the flow of blood to
prevent the oxygen rich blood and the carbon dioxide rich blood from mixing. In addition to
breathing oxygen through their skin when in water, frogs can also detect low-pitched
sounds through their skin. Another highly developed system is a frog's sense of sight and
smell (which again are both part of the nervous system). Frogs detect predators and prey
using their large eyes. Their eyes however have poorly developed eyelids, which do not
close. In order to close its eye, a frog has to draw the eye into its socket! There is a third
eyelid, known as the nictitating membrane. It can be drawn over the pulled in eye (eyeball).
Activity Questions
1. Identify the structures listed below and draw them on a blank sheet of paper.
_____glottis
_____tongue
_____ internal nostrils
_____ maxillary teeth
_____ vomerine teeth
_____ esophagus.
_____ stomach
_____ liver
_____lungs.
______small intestine
2. Based on what you know about frogs, why do frogs have small lungs?
3. What organ was the largest in the abdominal cavity?
4. Based on what you know about the digestive system, why is the small intestine so much longer
than the large intestine?
5. Why do you think that the hind limbs of the frog are more muscular than the forelimbs?
6. Complete the diagram of the Frog’s internal organs using the proper drawing and labeling
techniques learned in the course.