Snakes breathe, and like all vertebrates, they require oxygen for survival, but their respiratory system is highly specialized to accommodate their long, narrow body shape. This unique anatomy allows them to consume large prey without suffocating, a feat impossible for most other animals. Adaptations involve a single functional lung, the absence of a diaphragm, and a highly mobile airway, contributing to a respiratory mechanism unlike that of mammals.
Unique Lung Structure
The serpentine body plan necessitated a reshaping of the respiratory organs, resulting in most species having only one functional lung. The right lung is typically elongated and can stretch for a significant portion of the snake’s body length, while the left lung is often greatly reduced or vestigial to make room for other organs. This single, dominant lung is divided into two distinct functional sections that facilitate gas exchange and air movement.
The anterior section is the vascular lung, which contains the respiratory tissue where oxygen and carbon dioxide are exchanged with the blood. This portion is highly vascularized, making it the primary site for respiration. Air then moves toward the posterior section, known as the saccular lung or air sac.
This posterior region is a thin-walled, non-respiratory membranous sac that contains few blood vessels and does not facilitate gas exchange. Instead, the saccular lung acts as a simple air reservoir or bellows, a feature important for maintaining air flow when the forward part of the snake’s body is restricted. Air enters the system through the glottis, a small slit-like opening on the floor of the mouth, which leads directly to the trachea, or windpipe.
How Snakes Move Air
Unlike mammals, snakes do not possess a diaphragm, the sheet of muscle that separates the chest and abdominal cavities. Instead, the mechanical process of snake breathing relies on the movement of the ribs and the intercostal muscles located between them. This method is known as costal respiration, where the muscles contract to expand and contract the rib cage, creating the necessary pressure changes to move air in and out of the lung.
Inhalation occurs when the intercostal muscles contract, pulling the ribs outward and forward to increase the volume within the body cavity, which draws air into the lung. Exhalation is a more passive process, as the muscles relax and the rib cage returns to its resting position, pushing the air out. Forcing air out quickly, such as in a defensive hiss, involves a more forceful contraction of these same muscles.
This reliance on the rib cage gives snakes a modular system of breathing. If one part of the body is immobilized, such as during constriction or movement, the snake can shift the muscular action to an unrestricted section of its rib cage to continue ventilating the lung.
Breathing While Consuming Prey
The ability to swallow prey much larger than their own head presents a significant challenge to a snake’s ability to breathe, as the meal can fill the mouth and throat, blocking the airway. To circumvent this, the snake employs a specialized anatomical solution involving the glottis. The glottis is a firm, tubular structure that can be actively extended forward and laterally within the mouth cavity.
This extension allows the snake to project the opening of its windpipe past the edges of the obstructing prey, effectively creating a snorkel. This breathing tube remains open to the air at the front of the mouth, ensuring a continuous supply of oxygen to the trachea and lung while the slow swallowing process occurs. This adaptation is particularly important because the act of swallowing can sometimes last for hours, and the snake’s entire body may be constricted by the large mass of food.
Furthermore, the posterior saccular lung plays a supporting role during the meal, acting as a reservoir to store air and assist in the movement of gases deep into the lung. Maintaining respiration by extending the glottis and utilizing the specialized lung structure allows the snake to consume enormous meals without the risk of suffocation.