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Reptile Circulatory System

Reptile Circulatory System
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  • 0:03 The Reptile Circulatory System
  • 1:15 Reptilian Hearts
  • 3:19 Reptile Veins
  • 3:51 Reptile Arteries
  • 4:26 Special Adaptations
  • 5:39 Lesson Summary
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Lesson Transcript
Instructor: Taormina Lepore

Taormina has taught advanced high school biology, is a science museum educator, and has a Master's degree in museum paleontology.

In this lesson, we'll delve into the reptile circulatory system. The lesson will cover the structure and function of reptile blood vessels and heart structure, as well as special adaptations of these systems.

The Reptile Circulatory System

Lub-DUB. Lub-DUB. Lub-DUB. The sound of your very mammalian heart has a familiar and comforting rhythm. But what about reptiles? If you could press your ear against the chest of a crocodile (which I wouldn't recommend), or a lizard, or a turtle, would you hear the same sound?

Our mammalian circulatory system is superbly adapted for a speedy metabolism, just like bird circulatory systems. Reptiles, in contrast, have a circulatory system that falls somewhere between rapid bursts of energy and long, lethargic days basking in the sun.

All reptilian circulatory systems have a heart, blood vessels, including veins and arteries, and blood, just like mammals and birds. Not all reptiles have the same exact circulatory structure, though, especially with regard to the heart. We can trace the path of blood through a reptile's body to get a complete picture of how this remarkable group of animals exchanges oxygen and carbon dioxide and gathers energy from environmental heat.

Along the way, we'll take a look at the overall structure and function of reptilian hearts, blood vessels, as well as more specialized adaptations of reptilian circulation.

Reptilian Hearts

Let's imagine you're a blood cell in a reptile's body, and you're in the animal's heart. The maze you make your way through will vary in structure, depending on the reptile. During this discussion, remember that 'arteries move away' from the heart, and 'veins move toward' the heart. This will help you remember the flow of blood through veins and arteries.

Three-chambered hearts are present in most reptiles. Like our four-chambered human hearts, three-chambered hearts have two upper atria. Unlike our own hearts, a three-chambered reptile heart has one large ventricle, or lower and more muscular portion of the heart.

B. Lizard, turtle, and snake heart anatomy, with three chambers.
lizard heart

In this single ventricle, both oxygenated - or oxygen rich - and deoxygenated - or oxygen poor - blood can mix together.

If you're a deoxygenated blood cell, you want to pick up oxygen in the lungs. So, you travel into the heart via a large vein, the sinus venosus, and enter the right atrium. The right atrium then pushes the blood cell into the single lower ventricle, which pushes blood into the lungs through the pulmonary arteries. There, the blood cell will pick up oxygen.

Oxygenated blood moves from the lungs through the pulmonary veins and into the left atrium and the main ventricle, where the path of the oxygenated and deoxygenated blood crosses. The vast majority of the oxygenated blood is pushed out of the heart through the aorta, a major artery. Mixing of the blood is kept to a minimum through differential pressure during the beating of the aorta versus the ventricles. That gives the typical reptile heart a lub-DUB sound, though it is not quite as forceful as the sounds that our heart valves make when they are forced shut.

C. Crocodilian heart, with four chambers.
crocodilian heart

Crocodiles have a four-chambered heart with a fully divided set of atria and ventricles. The septum tissue that divides the heart in the middle is not perforated, like it is in other reptiles' three-chambered heart - where oxygenated and deoxygenated blood cross the same path. Very little mixing of oxygenated and deoxygenated blood (purple) occurs in crocodilians.

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