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The frog is among a handful of small animal species that serve as laboratory specimens for hands-on learning. The placement and structure of the frog's internal organs are very similar to humans', though of course more simplistic, making them a suitable tool for teaching internal anatomy. The frog is usually the first animal a biology student will dissect, in high school or junior high.
The internal organs in the chest and abdominal regions of a frog sit in a single cavity called the coelom. The respiratory organs consist of the trachea and lungs. The trachea is the windpipe, allowing the passage of air down to the lungs, which are hollow, thin-walled sacs used for respiration. They are housed in the upper or thoracic portion of the coelom.
The frog’s circulatory system organs consist of the heart, blood vessels and spleen. The heart has three chambers: two atria that receive oxygenated blood from the lungs and a single ventricle that pumps blood to the body. Veins and arteries are tubes that move blood to and from the heart, respectively. The spleen stores and recycles old red blood cells and is located within the mesentery between the stomach and large intestine. The heart is located in the center of the body between the forelimbs.
Digestive system organs include the esophagus, stomach, large intestine, small intestine, pancreas, liver, gall bladder and cloaca. The esophagus is the tube that allows food to travel from the mouth to the curved, white stomach sac. Food then continues to the coiled tubes called the small intestine where most digestion and nutrient absorption occurs. Digestive juices such as bile are made by the liver and pancreas. Bile is stored in the gall bladder. Undigested matter, or waste, passes from the small intestine, collects in the large intestine and is stored in the cloaca for excretion. The liver, the largest organ in the coelom, has three lobes. It is reddish-brown. The gall bladder is a small yellowish-green sac located under and attached to the liver. The feather-shaped pancreas is underneath the stomach.
The frog's urinary system organs include the kidneys, ureter, bladder and cloaca. Urine is produced in the kidneys and passed through tubes called ureters directly to the cloaca for excretion, or to the urinary bladder for storage before moving to the cloaca. The bladder, a thin membranous sac, is usually deflated unless filled with urine. The kidneys are reddish-brown and located on either side of the backbone, deep within the cavity.
In a male frog, the reproductive organs are the testes. In a female, they are the ovaries and oviduct. The testes are yellowish, oval and attached to the kidneys. The testes produce sperm, which travel to the cloaca. The ovaries produce eggs which move through the coiled, white oviducts to the cloaca. The cloaca can be considered a reproductive organ because it is a sac where urine, feces, sperm and eggs are collected and passed.
Frogs store energy for hibernation, or when food is scarce, in yellow finger-shaped organs called fat bodies. These are located in the abdominal cavity surrounding the large intestine.
- frog macro - a tree frog ( litoria caerulea ) isolated on white image by Christophe Fouquin from Fotolia.com