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Watch a Frog Eat Dinner
Watching a frog eat can be very entertaining. Did you ever wonder how they digest their food? The digestive system of a frog has to work efficiently, since they do not chew their food as we do. Let's take a look at how this all works.
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A Two-Part System
There are two major parts to a frog's digestion: the alimentary canal and the digestive glands.
The Alimentary Canal
This is what most people think of when they hear "digestive system" of a frog:
- Mouth and buccal cavity, pharynx, esophagus, stomach, small intestine, large intestine, cloaca
The Digestive Glands
No digestive system would work without digestive juices. Here are the main glands that produce these juices to help the frog with digestion:
- Gastric glands, liver, pancreas, intestinal glands
Here is a free downloadable diagram to help as a visual aid when studying this system.
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Understanding the Alimentary Canal
A baby frog, or a tadpole, feeds on plants such as algae and plankton. The adult frog, however, is a carnivore, eating mainly insects such as spiders, slugs, worms, or any other moving or living thing that will fit into its mouth.
For this reason, gardeners love frogs for their pest control abilities. Larger frogs can eat small animals such as rats, baby chickens or ducks. It is necessary to understand what an adult frog eats to be able to understand its digestive system, its organs, and why it works the way it does.
A frog's digestive system obviously begins with its mouth. Although frogs have two sets of teeth in the buccal cavity, they do not use them to eat their prey. These are used to hold the prey until it can be swallowed. The male frogs have a pharynx, which is in the throat on the way to the esophagus.
This is where the male vocal sacs are, and basically are openings of the eustachian tubes, connecting to the male's gullet and esophagus. Here is how it works:
- The tongue brings the food into the mouth, where the teeth hold the food if needed until the frog swallows its prey whole.
- Once the food is swallowed, or ingested, it passes through a very short esophagus to a much larger stomach.
- The stomach is a holding tank of sorts for the frog. However, very shortly after entering the stomach, the digestion process begins.
- When the food is digested enough, it enters a region called the pylorus. This is where the muscular pyloric valve works to send the food into the small intestine.
- The small intestine is a thin tube that consists of an area that is enlarged called the duodenum, which is joined to the stomach and the coiled ileum. It coils often, allowing for more absorption of food.
- When the dissolved food passes through the duodenum, it gets absorbed through the walls of the intestines into the bloodstream.
- Next, the small intestine dumps what is left into the short and stubby colon, or large intestine.
- From here, all of the remaining indigestible waste is pushed through the short, tubular cloaca, and then exits the body. Both liquid and solid wastes exit the body through the cloaca, as well as sperm and eggs during reproduction.
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There are gastric glands inside the walls of the stomach. They are needed to begin the process of digestion. They pump out gastric juices which contain HCI and protein-digesting enzymes.
The liver also contributes to digestion in a frog. It is a three-lobed organ that dominates the frog's body cavity. It produces bile, which is an ingredient needed to assist in digestion. The bile collects in the gallbladder, which is like a sac, and flows to the upper portion of the small intestine through the common bile duct. Another function that the liver provides is a storage center for digested food.
The pancreas plays a role in digestion as well. It is a small strip of cream-colored tissue near and parallel to the stomach. Pancreatic secretions are passed into the small intestine through the common bile duct. These juices include many enzymes like trypsin, lipase, amylase, chymotrypsin, etc.
There is a transparent membrane that houses the digestive organ called mesenteries. The function of mesenteries is only to bind the organs to the dorsal body wall. This is where the blood vessels flow from the mesenteries to the internal organs.
Finally, the intestines produce enzymes in the intestinal juice that helps in digestion.
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The Digestive Process: Creating One Function
The frog sees his prey and catches it with his bi-lobed tongue. Next, the frog holds larger prey with his teeth before swallowing. After swallowing, the food begins to digest as the stomach pumps out enzymes and HCI, and they begin doing their job. Now the food, which is only partially digested, is sent to the first part of the small intestine and duodenum.
The gallbladder sends out bile it receives from the liver, and the pancreas sends out pancreatic juices. Bile begins breaking down the fat, and the pancreatic juices take care of the carbs and proteins. Digestion is shortly completed in the intestines. Finger like folds in the intestines called villi and microvilli aid in the nutrients being absorbed into the bloodstream.
What's left of the food is not digestible and is met with water. It then exits the frog's digestive system through the cloaca and the cloacal vent.
The solid waste passes into the cloaca and on out the rectum.
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So, there you have it. A frog digests its food in a similar fashion as humans--but there are differences as well. Be sure to look for other topics in this series, and feel free to leave a comment or question at the end of this study guide.
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The author's own education on the subject.
Thomas E. Porch,DMD; Brad R. Batdorf, MAEd "Biology Third Edition, with Laboratory Exercises" BJU Press, 2005.
Author unknown. "Digestive System of a Frog", http://www.tutorvista.com/biology/digestive-system-of-a-frog
Author unknown. "Frog Dissection", http://www.biologyjunction.com/frog_dissection.htm
Author unknown. "Flashcards: Important Frog Parts of the Digestive System", http://quizlet.com/300679/important-frog-parts-of-the-digestive-system-flash-cards/
Drawings: by Atlanta Page ©2011
Image: Author-Arpingstone "Blue Poison Dart frog Dendrobates azureus at Bristol Zoo, England" under public domain.
What's For Dinner? A Frog's Digestive System
This series was created to simplify the sometimes overcomplicated body systems and internal anatomy of a frog. Covered in this series is a frog's digestive system, circulatory system, and muscular system. These articles are easy to read yet thorough, with great pictures to enhance your experience.