The function of the respiratory system in humans is to move oxygen from the outside environment into the body and to remove carbon dioxide and other wastes from the body.
How, you might wonder? These processes actually involve a number of organs, as pictured in the diagram. First, air enters the body through either the nose or the mouth. From there, the air passes through a series of tubes that carries it into the lungs.
Within the lungs are small structures which allow for the passage of the oxygen into the blood and carbon dioxide to move out of the blood back into the lungs. At this point, the air is pushed back up and out through the nose.
Frogs have a specialized system of organs called the respiratory system which are responsible for moving oxygen from the outside environment into the body and removing carbon dioxide and other wastes from the body. This process begins when the frog draws air into its body. In some ways this process is quite similar to humans. For instance, the frog may bring in air through nostrils which are located on the front of its head. Or, air may be brought in as the frog opens its mouth and fills it with air. Either way, once the air is inside, the frog raises the floor of its mouth upward. The force of this motion pushes the air downward towards the frog’s lungs. Once in the lungs, specialized structures exchange the oxygen into the frog’s blood and remove the carbon dioxide and other waste gases from the blood. The frog then pushes the air containing these wastes back out of its body.
One other organ that should be mentioned when discussing the respiratory system of frogs is the skin. The frog's skin serves as an additional organ for gas exchange. However, it must remain moist to do this, which is one reason that frogs, like other amphibians, live in moist places.
In some ways, the fish respiratory system may seem the most different from that with which you are familiar.
But, a closer look reveals that the purpose of the system is still the same.
The respiratory system in fish is responsible for moving oxygen from the outside environment into the body and removing carbon dioxide and other wastes from the body. Even more, the fish has specialized structures within its body which allow this process to occur.
First, the fish takes in water through its mouth. The water then flows over the gills which are located directly behind the mouth. Within the gills are structures called gill filaments. As the water moves over the gill filaments, the oxygen from the water is moved into the blood and carbon dioxide and other waste gases are passed back out of the blood into the surrounding water. The water then continues out of the fish’s head through the opening behind the gills.

nostril
Bronchi lung mouth
Pharynx
Lung
Bronchi
Structures within the lungs
Nose
Mouth
Trachea http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/
A/AnimalHearts.html
Gill filaments http://www.vandykestaxidermy.
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Human
The human circulatory system consists of the heart, blood, and blood vessels.
These structures work together in order to carry needed substances to cells and to carry waste products away from cells.
Each structure contributes to the overall functioning of the system. For example, blood carries oxygen and nutrients to cells and carries waste products away from them. Next, the blood vessels provide a network of tubes to carry the blood throughout the body. Finally, the heart acts as a pump. Each time the heart beats, it pushes blood through the blood vessels of the circulatory system.
The human heart is made up of four separate sections, or chambers. As the blood flows into and through the heart, the structure of the heart ensures that the blood will only flow in one direction.
Frog
The frog circulatory system consists of the heart, blood, and blood vessels.
These structures work together in order to carry needed substances to cells and to carry waste products away from cells.
Each structure contributes to the overall functioning of the system. For example, blood carries oxygen and nutrients to cells and carries waste products away from them. Next, the blood vessels provide a network of tubes to carry the blood throughout the body. Finally, the heart acts as a pump. Each time the heart beats, it pushes blood through the blood vessels of the circulatory system.
The frog’s heart is made up of three separate sections, or chambers.
Perch
The circulatory system in fish consists of the heart, blood, and blood vessels.
These structures work together in order to carry needed substances to cells and to carry waste products away from cells.
Each structure contributes to the overall functioning of the system. For example, blood carries oxygen and nutrients to cells and carries waste products away from them. Next, the blood vessels provide a network of tubes to carry the blood throughout the body. Finally, the heart acts as a pump. Each time the heart beats, it pushes blood through the blood vessels of the circulatory system.
The structure of the fish’s heart and circulatory system is actually rather simple, and is such that blood can only flow in one direction. If you look at the diagram, you will notice that the fish’s heart is made up of two separate sections, or chambers.

Human
The nervous system receives information about what is happening both inside and outside your body. It also directs the way in which your body responds to this information. In addition, your nervous system helps keep your body stable. The nervous system carries messages from the brain and spinal cord to all other parts of the body and back again. The system consists of the brain, spinal cord, and nerves. Some nerves make it possible for the muscles of the body to move when you want them to, while other nerves control things we don’t think about, like our heartbeat.
Frog
The nervous system of the frog is responsible for directing the way it responds to what is happening both inside and outside of the frog. The nervous system carries messages from the brain and spinal cord to all other parts of the body and back again. The system consists of the brain, spinal cord, and nerves. One set of nerves makes it possible for the muscles of the body to move on command, such as swimming, and the other set regulates things like breathing.
Perch
The nervous system of the perch is responsible for directing the way it responds to what is happening both inside and outside of the fish. The nervous system carries messages from the brain and spinal cord to all other parts of the body and back again. The system consists of the brain, spinal cord, and nerves. One set of nerves makes it possible for the muscles of the body to move on command, such as swimming, and the other set regulates things like digestion.

The human digestive system is comprised of a tube that has two openings, one for the entrance of food and water and one for the exit of wastes.
The essential function is the same as that in other multicellular organisms, to break large food molecules down into small molecules that can pass through cell membranes. Food enters the human digestive tube through the mouth and travels down the tube through the esophagus, stomach, small intestine, and large intestine, and any wastes exit out of the rectum. Most of the digestion and absorption take place in the small intestine. Digestion is aided by digestive fluids and waves of muscular contraction that move along the digestive tract.
The frog digestive system, like the human digestive system, consists of a tube with two openings. A frog captures food in its mouth and the food is forced through the digestive tube to the esophagus, stomach, small intestine, and large intestine. Any leftover waste then exits the body. Most digestion and nutrient absorption takes place in the small intestine. The essential function of the digestive system is the same as that in other multicellular organisms, to break large food molecules down into small molecules that can pass through cell membranes.
The perch is a complex multicellular organism with a digestive system that breaks down food into small molecules that can be used by the cells. The perch is carnivorous. When a perch catches its prey, the food enters the body through the mouth where it is ripped apart by sharp teeth. The pieces of food are moved into the esophagus, stomach, and into a very short intestine. The intestine is shorter than the frog and human’s intestines because the food consumed by the perch doesn’t take very long to be digested and absorbed.
The essential function of the digestive system is the same as that in other multicellular organisms, to break large food molecules down into small molecules that can pass through cell membranes.

Blood vessels
Blood vessel s
Oxygenpoor blood
Oxygen-rich blood
Figure 1: The position of the heart and major blood vessels of the frog
Source: www.digitalfrog.com/resources/archives/circ.jpg heart
Figure 2: The internal structure of the frog’s heart, and the relationship to other body structures
Source: http://www.estrellamountain.edu/faculty/farabee/ biobk/BioBookcircSYS.html
Blood vessel
Heart
Blood vessel to lower body
Heart

Brain
Nerves
Spinal Cord