Frogs Have Heart: A Look at a Frog's Circulatory System
By Atlanta Page
Did you ever feel a frog's heartbeat or pulse? This study guide is part of a series designed to make learning about a frog's circulatory system fun and easy. Follow the links to download diagrams of both the heart and the entire circulatory system.
A Frog's Heart Is Central to Its Circulation
If you look at a diagram of a frog's circulatory system, you will notice the heart is different than ours. It has two atria and a single ventricle, making it have a total of three chambers. Here's how it works.
Deoxygenated blood is sent to the atrium from various organs in the frog's body through blood vessels and veins. This is the blood being drained from organs, thus starting the cleansing process. Oxygenated blood then comes from the lungs and the skin, and enters the left atrium. (This also serves as a gas exchange in most amphibians.)
Both atria dump their blood into the single ventricle. The ventricle is divided into two narrowly separated chambers, which cleverly reduces the mixing of oxygenated and deoxygenated blood together. The ventricle contracts, sending oxygenated blood to the brain from the left ventricle. It reaches the head by flowing through the carotid arteries.
This is an almost pure blood that reaches the brain.
The skin and lungs receive nearly pure blood from the right atrium through pulmocutaneous arteries. From the skin and lungs, fresh oxygen can be picked up. The blood that passes through the aortic arches is very mixed up, but still has a lot of oxygen in it. There is enough to supply the rest of the body what it needs.
Interesting note: Both the gas exchange organs and the interior tissues of the body get their blood under full pressure.
There are some basic rules of circulation that apply to all living creatures. Understanding this will make it much easier to understand how the frog's circulation is efficient in its makeup.
An efficient circulatory system has the following:
First, there must be a source of fluid to carry the nutrients, which in this case, would be blood.
Next, you need a system of vessels to carry the blood to its destinations.
Most importantly, a pump is needed to pump the blood through the system.
There must be exchange systems, or organs that serve as bridges between nutrients or pollution from the outside to the inside of the system. In this case, that would include the lungs and intestines, which add nutrients to the blood, and again the lungs and also the kidneys to help remove materials from the blood.
The most important part of a circulatory system besides the heart would be the lungs. This organ serves as a gas exchange center. It fulfills the demand for the transport of oxygen and carbon dioxide to and from a gas exchange organ.
All exchanges between the cells and the blood occur in the capillaries. This is always the case in a circulatory system. The force of the pump, or the heart in this case, pushes blood through the arteries. The blood dissipates as it flows through the capillaries. Because the capillaries are spread out all over the body, they end up being bigger than an artery in comparison. Although tiny in size, the individual area the capillaries cover is greater than the artery that supplies them the blood.
A Frog's Working Circulation
We learned how a frog's pump or heart works as well as the basics needed for an efficient cardiovascular system. Now let's see how a frog's circulatory system actually works as a whole.
Blood circulates through the capillaries in the lungs and gathers oxygen in the process. Then it flows on through the pulmonary vein into the left atrium of the heart. At the very same time, blood from the body's organs and muscles that has been deoxygenated flows through the vena cava. The vena cava is comprised of three large veins.
Next, the blood travels to a thin sac at the back of the heart called the sinus venosus. This sac empties into the right atrium. Once filled, both atria contract at the same time. This empties the blood into the muscular ventricle. Now the ventricle is ready to contract, forcing oxygenated and deoxygenated blood through a single large vessel. This large vessel is called the conus ateriousus. From the conus ateriousus, there are three branches coming out called carotid arches. These include the carotid arch, which sends blood to the head, the pulmocutaneous arch, which sends blood to the lungs and skin, and the aortic arches, which fuse into the single dorsal aorta taking blood to the body, organs, and muscles.
Once the aortic arches fuse into the dorsal aorta, the blood then goes specifically through the coeliacomesenteric artery. Next, blood is divided, and some goes to the coeliac artery which sends blood to the stomach and pancreas. The other half of the blood is sent to the mesenteric artery that goes to the intestine and spleen. After this, the blood is sent to the legs. It is divided and sent through two common iliac arteries.
Finally and simultaneously, the carotid arches send blood to the head through a pulmocutaneous artery, while sending blood further to the lungs and skin. Because of this amazing process, the frog is alive and ready to jump, eat, sleep, and breathe.
I hope you learned something new about frogs and their circulation system today. Feel free to leave a comment at the bottom.