(08/29/2025) Respiratory System and Vocalization in Tetrapods
Respiratory System in Tetrapods
Ventilation Mechanisms
Tetrapods use lungs as the primary respiratory organ.
Ventilation involves moving air in and out of the body.
Terrestrial vertebrates access the pharynx through the nostrils or mouth.
The pharynx is posterior to the oral cavity.
Air flows via a tube system from the pharynx to the lungs.
A single trachea usually extends down the neck.
Larynx and Sound Production
The glottis is guarded by paired cartilages that control its opening.
The larynx, a chamber leading to the lungs, often has membranes.
Membrane tension and airflow cause vibrations, producing sound.
Anatomy of the Neck
The larynx can be palpated in the neck.
C-shaped cartilaginous rings are palpable below the thyroid cartilage.
Neural spines of cervical vertebrae are also palpable on the back of the neck.
The dorsal portion of the neck houses the cervical vertebrae.
The respiratory tree is located in the front, ventral area of the neck.
Esophagus is typically collapsed in the neck.
The trachea is reinforced with cartilaginous rings to prevent collapse.
These rings are C-shaped, with the open portion adjacent to the esophagus.
Epiglottis and Glottis Control
Cartilages at the glottis control the glottal opening.
The epiglottis covers the glottis during swallowing.
This prevents food from entering the trachea.
The glottis leads into the larynx.
The larynx contains soft tissue cords for sound production by vibration.
Vocalization in Frogs
Frogs use vocal sacs to produce calls.
Some species have single or paired vocal sacs.
Bullfrogs have internal vocal sacs.
Frogs inhale air into the lungs, then force it out through the trachea and larynx.
Air passes into the oral cavity and then into the vocal sac.
The vocal sac acts as a resonating chamber.
Frogs can recycle air from the vocal sac back into the lungs for sustained calling.
Specialized Structures
The larynx's position changes with age and impacts feeding.
Snakes have a protrusible glottis, allowing them to breathe while eating large prey.
Components of the Larynx
The epiglottis, larynx, thyroid cartilages, arytenoid cartilages, and cricoid cartilages are present.
C-shaped rings form the trachea walls.
False Vocal Cords
Monkeys and cats have false vocal cords.
These animals can produce sounds with both vocal cords and false vocal cords simultaneously.
Hyoid apparatus supports the false vocal cords.
This structure is connected to a large vessel.
Trachea and Hiccups
The trachea connects the pharynx to the lungs.
Hiccups are caused by disruptions of the phrenic nerve and diaphragm function.
Airway Anatomy
The glottis leads to the laryngeal area and then the trachea.
The trachea bifurcates, sending a branch to each lung.
Smooth muscle above the trachea can constrict.
Birds have two sets of tracheal rings: large outer rings and smaller inner rings that separate during neck extension.
Bronchi and Bronchioles
The modified tube after bifurcation is the bronchus.
Bronchi is the plural form.
The glottis and larynx lead to the trachea, which bifurcates into two bronchi
These structures are reinforced with cartilaginous rings and muscle.
The bronchi continue to bifurcate within the lungs.
This creates a large surface area, especially in mammals.
Bronchi transition into smaller tubes called bronchioles.
Syrinx in Birds
Birds lack a larynx and vocal cords.
Instead they produce sound in a specialized chamber: the syrinx.
The syrinx is at the point where the trachea bifurcates into the paired bronchi.
Syrinx can be tracheal, bronchial, or bronchotracheal.
Buccal Pumping in Frogs
Frogs use buccal pumping to ventilate their lungs.
The nares have sphincter muscles.
When the nostrils and glottis are closed and the frog depresses the floor of the oral cavity, the pressure decreases.
With open nostrils, air is sucked into the oral cavity.
The floor of the mouth acts as a piston.
With nostrils closed, the air from the oral cavity is forced into the lungs.
Salamanders with lungs use similar respiration.
Diaphragm and Lung Structure
Frogs don't have a diaphragm.
Most tetrapods lack a muscularized diaphragm separating the lungs from the abdominal cavity.
Mammals and crocodilians have evolved diaphragms independently.
Lungs can extend far back into the body, into the pleural peritoneal cavity.
There is no separated thorax and abdomen; it is one central cavity.
There are structural difference in different animals.
Lung Partitioning and Faveoli
Animals evolve partitions that partially go into the lungs.
Each partition has respiratory membranes.
Tubes leading into the lungs branch and service the partitioned areas.
These partitioned areas are called faveoli.
A single tube services many faveoli.
Faveoli are found in ectothermic animals, which have lower oxygen demands.
Faveoli do contain some cartilage for rigidity.