The glottis is a small, highly functional opening located within the frog’s oral cavity. This structure acts as a controlled passage point, managing the flow of air for two fundamental life processes: respiration and sound production. Its function involves precise coordination with the respiratory system and the mechanism of sound production.
Where the Glottis is Located
The glottis is situated on the floor of the frog’s mouth, positioned toward the back of the pharynx. It appears as a small, vertical or slit-like opening just posterior to where the tongue attaches. This location is immediately anterior to the large, round opening of the esophagus. The glottis is the direct entrance to the larynx, serving as the sole gateway connecting the external environment, via the mouth and nostrils, to the lungs. Its precise position allows it to operate as a valve in amphibian breathing.
The Glottis as the Gateway to the Lungs
The primary function of the glottis is to manage air intake for pulmonary respiration. Frogs do not possess a diaphragm like mammals, so they cannot draw air into their lungs by creating a vacuum. Instead, they rely on a positive pressure mechanism called buccal pumping to force air into the lungs.
The glottis controls this positive pressure system. Air is first drawn into the mouth cavity by lowering the floor of the pharynx while the nostrils are open. Once the mouth cavity is full, the nostrils close, and the glottis opens only momentarily. The floor of the mouth then rises, forcibly pushing the collected air through the glottis and down the trachea into the lungs.
Acting as a protective valve, the glottis ensures that air is directed exclusively into the respiratory tract. During swallowing, the glottis snaps shut to prevent food or water from entering the lung tissue. This protective closing mechanism keeps the airway clear, preventing a blockage that could stop gas exchange.
Generating Sound: Vocalization in Frogs
Beyond its respiratory role, the glottis is essential to the frog’s ability to vocalize. The glottis opens into the larynx, a cartilaginous structure that contains the vocal cords. These cords are elastic bands that vibrate when air is rapidly forced across them.
The sound is generated when the frog pushes air from the lungs, through the glottis, and past the taut vocal cords in the larynx. This vibration creates the species-specific croak, chirp, or trill used for mating calls, territorial defense, or distress signals. Although the glottis is the opening, the surrounding laryngeal structure is the actual source of the sound vibration.
In many male frogs, the sound created by the vibrating vocal cords is amplified by the use of vocal sacs. These elastic pouches, connected to the oral cavity, inflate with air during calling. The vocal sac acts as an acoustic resonator, helping to project the call over long distances.