The elongated and limbless body of a snake possesses a respiratory system well-adapted to its form and lifestyle. Understanding how these reptiles ventilate their bodies reveals fascinating evolutionary solutions to living in a long, narrow configuration.
Snakes Possess Unique Lungs
Snakes do have lungs. Their lung structure differs significantly from that of mammals due to their elongated bodies. Most snake species have only one functional lung, which is the right lung. The left lung is greatly reduced in size, vestigial, or even completely absent. This asymmetrical arrangement is an adaptation that allows for efficient organ packing within their narrow body cavity. The functional right lung stretches across a significant portion of the snake’s body.
This primary lung is divided into two regions. The anterior portion, closer to the head, is the vascular lung where gas exchange occurs. The posterior part functions as a thin-walled air sac, acting as a reservoir for air but not participating in gas exchange. This design maximizes the surface area for oxygen absorption within the constraints of their body shape.
The Mechanics of Snake Respiration
Snakes breathe differently from mammals, as they do not possess a diaphragm. Instead, they rely on the intercostal muscles located between their ribs to facilitate breathing. When these muscles contract, they expand the rib cage, creating negative pressure that draws air into the lungs. Relaxation of these muscles then expels the air.
The glottis, a small opening behind the tongue that leads to the trachea, is closed, forming a vertical slit, opening only when the snake takes a breath. The glottis can extend outside the mouth, particularly when the snake is swallowing large prey. This enables the snake to continue breathing even while its mouth and throat are occupied by a meal.
Some snake species also possess a “tracheal lung,” an extension of the trachea. This structure provides an additional surface for gas exchange, enhancing respiratory efficiency. The tracheal lung is particularly beneficial during situations where normal lung function might be impaired, such as during constriction of prey.
Diverse Respiratory Adaptations in Snakes
Variations in lung structure and function exist across different snake species, reflecting their diverse habitats and behaviors. For instance, boas and pythons are exceptions, as they retain two lungs, although the left lung is still smaller than the right. In boas, the right lung can extend for up to a third of their body length, while the left lung is reduced or non-functional. This dual lung presence is considered a more primitive trait within snake lineages.
Aquatic snakes exhibit specialized adaptations for their underwater existence. While they are air-breathers and must surface for air, some sea snakes have highly vascularized lungs that aid in buoyancy control and prolonged dives. Certain species, like the annulated sea snake, can absorb a significant amount of oxygen through their skin, a process known as cutaneous respiration, which helps extend their time submerged, with some species capable of staying underwater for up to eight hours.
Arboreal snakes, which spend much of their lives in trees, utilize the same intercostal muscle-driven breathing mechanisms as other snakes. Their elongated body shape and unique lung structure allow them to breathe effectively even when coiled or navigating branches. The specific location of the respiratory portion of the lung can also vary between snake families; in boids and colubrids, it is typically between the heart and cranial liver, whereas in viperids and elapids, it is cranial to the heart.