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The Octopus Circulatory System

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  • 0:00 The Octopus
  • 0:59 The Human Circulatory System
  • 1:47 The Octopus: Three…
  • 3:01 The Systemic Heart
  • 4:06 Lesson Summary
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Lesson Transcript
Instructor: Danielle Haak

Danielle has a PhD in Natural Resource Sciences and a MSc in Biological Sciences

The octopus is a unique underwater creature that evolved more than 600 million years ago. One of the most interesting things about the octopus is that is has 3 hearts! Read this lesson to learn more about its peculiar circulatory system.

The Octopus

What can you tell me about an octopus? Probably that it lives in the water, has eight arms, is really good at camouflaging itself, and that it's a good hunter. All of those things are true, but did you also know that an octopus has three hearts?

The octopus is classified in the Phylum Mollusca, along with snails, slugs, and clams. However, it splits off from these creatures once you get to Class. The octopus is in the Class Cephalopoda, with the squid, cuttlefish, and clams. Cephalopods originated over 600 million years ago, so the octopus has been lurking in our waters for a long time! Cephalopods are a pretty diverse bunch, but they do have some things in common. They all have three hearts and larger brains than most invertebrates. They have eyes that rival the complexity of humans. All cephalopods are carnivores, meaning they only eat other animals. They are all capable of changing the color and pattern of their skin quickly, making them better hunters.

The Human Circulatory System

One of the most unique characteristics of the octopus is its circulatory system. To really understand why it's unique, let's first take a look at the human circulatory system, something you're probably more familiar with.

Humans have a closed circulatory system, which means that the blood is contained in a network of blood vessels inside the body. Our circulatory system has two main jobs. First, the heart pumps blood to the lungs to expel carbon dioxide, and to pick up more oxygen. Then the heart pumps this oxygenated blood around the body, where the blood delivers oxygen and nutrients to the cells, and picks up more carbon dioxide to be eliminated. Human blood is red because it contains the protein hemoglobin. Oxygen binds to hemoglobin, which contains iron. These are all things you already knew, right?

The Octopus: Three Hearts Are Better Than One

Now, let's take a look at the circulatory system of the octopus. Like humans, octopi have a closed circulatory system that delivers oxygen to the body and removes waste materials (carbon dioxide). However, that's where the similarities between us end. Most notably, the octopus has three functioning hearts. Like many other aquatic organisms, the octopus breathes through gills instead of lungs. The gills are the interface where gases (oxygen and carbon dioxide) are exchanged between the body and the water. They release waste materials and bind to dissolved oxygen in the water. They are made of a thin membrane with a lot of surface area to maximize the amount of gas that can be exchanged. The octopus forces water over its gills by contracting its muscles, expelling waste materials and absorbing oxygen. In fact, the octopus is so good at moving oxygenated water over its gills that it can get its blood oxygen concentration up to about 11%, compared to about 3% in other aquatic organisms. Two of the three hearts are located near the gills. They are smaller in size than the third heart, and their job is to pump blood to the gills where it can get rid of waste and pick up more oxygen. Then, these two smaller hearts pump the freshly oxygenated blood to the main heart.

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