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Anatomy Of A Frog

by e-Tutor Staff

In this lesson module you will learn about the different parts of a frog. You will also virtually dissect a frog.

Lesson Problem

What is the anatomy of a frog?


Study Guide

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 frog's head movement is limited due to the short, almost rigid neck. The trunk of a frog forms walls for a single body cavity known as the coelom. The coelom holds all of the frog's internal organs. Frogs have the same kinds of organs as humans and the same organ systems. 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. Humans have tongues and teeth as well (and a mouth of course).

If you closely examine the head of a frog, you will find the following: eye sockets, eyes, mouth, tongue, vomerine teeth, maxillary teeth, gullet teeth, external nostrils, internal nostrils, the glottis opening, eustachian tube openings, the tympanic membranes and the esophagus. The eyes, the mouth and the nostrils are all examples of a frog's external structures. In addition, a frog's external structures also include the webbed feet and the cloaca opening. The tympanic membranes or eardrums are exposed, but a frog does not have external ears. 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, the testes, the ovaries and fat bodies. Again, the frog has organs that are similar to those of humans. For example, a frog has a brain, kidneys, lungs, eyes, a stomach, intestines and a heart. The one major difference between the anatomy of a frog and that of humans is that the is simpler than the anatomy of a man. Frogs don't have ribs or a diaphragm. Humans have both and a diaphragm (thoracic diaphragm) plays 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.

A frog uses its tongue for grabbing prey. The vomarine and maxillary teeth are used for holding the prey. The internal nostrils are used by the frog for breathing. The tympanic membrane is the eardrum. It is located behind the frog's eyes. The eustachian tubes equalize the pressure in the frog's inner ear. The glottis is a tube, which leads to the lungs, while the esophagus is a tube which leads to the frog's stomach. The stomach helps the frog break down food and the liver also helps with digestion (it makes bile). Bile (also known as gall) is a fluid secreted by hepatocytes from the liver of most vertebrates (humans and frogs are vertebrates). Hepatocytes are cells present in the liver, and they 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 into the duodenum. Bile, therefore helps with digestion. The duodenum, which is 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 duodenum. The small intestine absorbs nutrients from food. The large intestine absorbs water. It also collects waste. You can also think of the cloaca as storing waste, as this part of the frog 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. A frog has very few bones. They make up the skeleton of the frog. The skull (head bone) is large and flat. The legs are long for jumping. In addition to being specialized for jumping, the bones in their upper and hind legs are also specialized for leaping. The muscles move the skeleton of the frog. The muscles help the frog jump and swim.

Frogs have other systems similar to humans that are a part of their bodies. For example, a frog has a nervous system (all of the nerves and the spine), a circulatory system (the heart and blood going through the body) and a digestive system (the food going through the mouth to the intestines). The heart (which is part of the circulatory system) is three-chambered. There are two atria and one ventricle. There is a valve within the frog's heart known as the spiral valve. It directs the flow of blood to prevent oxygenated and de-oxygenated blood from mixing. A frog's sense of hearing (which is part of the nervous system) is highly developed. Frogs can detect high-pitched sounds with their ears. 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). Frogs also use their sense of smell to detect chemical signals. These signals help them to identify potential food.

Now that we know the basics of frog anatomy, let's move onto the Activities and Extended Learning.


Extended Learning

Write some of the things you have learned about frogs from the Study Guide. Your answer should be in short essay format, 3-5 paragraphs. As you write the essay, answer the following questions in complete sentences, using your own words:

1. How are frogs adapted for aquatic life?

2. How are frogs adapted for terrestrial life?

3. If frogs have lungs, why do they also breathe through their skin?

Get a book or search the web for the human body. See if you can find the similarities and differences between a frog's anatomy and a human's anatomy. You should be able find some of the information in the Study Guide. You can also use the links provided in the Resources.

How are frogs and humans alike?

How are frogs and humans different?