Tortoise respiratory system — breathing inside a rigid shell
Overview of tortoise respiration — multicameral lungs fixed beneath the carapace, no diaphragm and no moving ribcage, and ventilation driven by abdominal muscle sheets and limb movement.
General educational reference only — not clinical or veterinary advice. Anatomy varies between individual animals; consult a licensed veterinarian for any health concern.
Airway and lungs
Air enters the nostrils, crosses the internal nares into the mouth and passes the glottis, a slit at the base of the tongue. The trachea is short and divides into two long primary bronchi near the base of the neck, an arrangement that keeps the airway patent when the head is withdrawn. The paired lungs are large and multicameral — divided into chambers whose walls are folded into a honeycomb of faveoli — and lie dorsally, attached beneath the carapace.
Breathing without a moving ribcage
The ribs are fused into the shell, so the chest wall cannot expand, and there is no muscular diaphragm; a non-muscular post-pulmonary septum separates the lungs from the abdominal organs. Ventilation comes instead from paired antagonistic muscle sheets at the limb openings. Contraction of the abdominal oblique enlarges the coelomic space and draws air in, while the transverse abdominis presses the viscera against the lungs to force air out.
Limb and head movement
Because the lungs sit above the viscera, any shift in the position of the abdominal contents moves air. Withdrawing the head and limbs into the shell displaces the viscera inward and expels air, while extending them lets the lungs refill. Breathing is therefore intermittent, occurring in bouts separated by pauses, and its rate follows body temperature as in other ectotherms.
