Unless you are an avid reptile keeper, you likely don’t know about reptiles beyond the basics taught in schools. One of the most common questions people have is how they breathe? Let’s find out.
Reptiles, including snakes, turtles, tortoises, crocodiles, alligators, and lizards, breathe air using their lungs. Reptiles use their lungs to take in oxygen and expel carbon dioxide.
Reptiles, including snakes, lizards, and tortoises, often have a bad reputation due to their unusual appearance and unpredictable personalities.
What Is A Reptile?
Reptilian animals belong to the class Reptilia, which encompasses air-breathing animals with epidermal scales and internal fertilization. Unlike amphibians, reptiles cannot absorb oxygen via their skin as the skin is covered in thick epidermal scales.
Reptiles are ectotherms, meaning they use their environment to regulate their body temperature. They are also oviparous, egg-laying animals. Most reptiles bury their eggs underground in soft sand or loose soil. The substrate acts as an incubator, and the temperature within the nest determines the gender of the hatchlings. Additionally, once the reptile eggs hatch, the young are generally self-sufficient and do not rely on their parents.
Species belonging to the class Reptilia include:
Due to their need for a warm environment, most reptiles live in countries near the equator where the temperature is hot for most of the year. Reptiles living in temperate climates will brumate during the colder months.
Although most reptile species still live in or near water, reptiles were the first class of animals to adapt to life on land.
Reptiles are not much different from humans when it comes to respiration and gas exchange. Reptiles breathe air and have a pair of lungs to take in oxygen and expel carbon dioxide.
Reptiles’ lungs have alveoli, tiny sacs that exchange gas with the capillaries (blood vessels) within the lungs. The technique used varies between reptile groups.
Squamates (snakes, lizards, and crocodiles) ventilate their lungs using the chest wall muscles, but each animal’s respiratory system is located differently. Snakes are long and thin, so their internal organs are laid out vertically and side-by-side.
Air is taken in through the nostrils and passes through a small opening called a glottis. Air travels along the trachea, which ends just before the heart.
The air is split along two bronchi, one leading to the left lung and one to the right lung. Snakes have one fully functioning lung (right side) and one vestigial lung.
Turtles And Tortoises
Reptiles like turtles and tortoises have a respiratory system different from most other animals. They have a hard shell covering most of their body, so they cannot rely on thorax muscles to regulate their breathing.
Instead, they have a ring of muscles connected to their shell, which encircles the lungs. This ring of muscles contracts to pull air into the lungs and then expands to force air out. Extinct tortoises did possess ribs, but approximately 260 million years ago, turtles and tortoises began to evolve to include the hard outer shell we see in modern species.
Many people believe turtles can breathe underwater, as they can remain submerged for such long periods. This is not the case. Turtles must surface to take gulps of air. It is not uncommon for female turtles to drown during mating, and every year, thousands of turtles drown when they get caught up in fishing nets.
Crocodiles And Alligators
Crocodiles and alligators have the most advanced respiratory system within the class of Reptilia. Their respiration is most similar to humans. They have an epiglottis that separates their airway and esophagus, a trachea connecting the mouth and lungs, and chest muscles expanding and contracting to control breathing.
To take a breath, the diaphragm muscle contracts. This pulls air through the nostrils, the epiglottis, and the trachea. Upon reaching the lungs, gas exchange occurs via the alveoli. Oxygen is passed via the alveoli into the capillaries, and carbon dioxide is then expired from the body when the diaphragm relaxes.
Unlike humans, reptiles have a unidirectional respiratory system. Instead of the air being separated equally between the two lungs, air enters one lung, then flows along a bypassed airway into the second lung before being expelled from the body. This form of respiration is more efficient as it increases the amount of oxygen in each breath.
Additionally, when crocodiles and alligators dive, their heart changes how oxygen is delivered. These animals have a valve called the foramen of Panizza. At rest, this valve is open, allowing free flow of oxygenated blood to the stomach and intestines. During a dive, this valve constricts, so oxygenated blood flows around the body, but low oxygen/high carbon dioxide blood goes to the digestive tract instead of the lungs.
The pulmonary artery also contracts during a dive, which reduces blood flow to the lungs. Most reptiles have a slow metabolism, so reduced oxygen supply during dives will not affect them. A crocodile will surface for air every 20-30 minutes, but they can dive for up to one hour.
By contrast, humans have a very high metabolic rate, and we typically take a breath every 2-5 seconds. This may extend to 10 seconds as metabolic rates slow down during sleep. Most humans can hold their breath for 30 seconds to one minute, but this can be extended to between 2 and 5 minutes with training.
In a small number of aquatic snakes, oxygen exchange can occur via the skin. This is because aquatic snakes have slightly different scales to reptiles living on land. Aquatic snakes still need to surface for air, but only a handful of times per day.
Bryan Harding is a member of the American Society of Mammalogists and a member of the American Birding Association. Bryan is especially fond of mammals and has studied and worked with them around the world. Bryan serves as owner, writer, and publisher of North American Nature.