As turtles live underwater, do they respire through lungs like reptiles or through gills like the fishes? Turtles have lungs, the primary respiratory organ, just like other reptiles.
Pulmonary respiration in the lungs
The respiratory organ begins with the nostrils, which are always open and lack valves. The mouth is held closed, and the air enters through the nostrils, moving to the glottis. The glottis opens and shuts to flow the air into the trachea, which flows into the lungs through the bronchi. The exchange of air with the bloodstream happens at the bronchioles. The carbon dioxide then flows back through the glottis and nostrils.
Lungs under the shell
Unlike a human who uses their diaphragm, which helps the lungs to inflate and contract, the turtles are handicapped with an immovable hard shell. Ventilation is achieved by the muscles lining their shells, from pelvic to shoulder girdles to plastron, which helps air move in and out. Also, turtles can alter the pressure in the lungs by moving the limbs in and out of the shell.
Turtles have lungs, but can they breathe underwater?
No, turtles cannot breathe underwater, but they can hold their breath for long periods of time. Compared to humans, who can hold their breath for a maximum of two minutes, turtles can hold their breath for 4-7 hours.
Do you know that turtles achieve this extended stay underwater by slowing their heart rate? The duration between two heartbeats in a turtle underwater is about 9 minutes compared to 0.8 seconds in humans. However, a turtle caught in a net gets stressed and can drown in minutes.
More ways to breathe
Since they live underwater, and coming out on the surface to breathe costs them energy and risk of life, turtles have devised alternate oxygen supply means. This gives small respite for the animal when underwater.
Lungs serve as a storage device for oxygen. Loggerhead sea turtles are reported to expire on reaching the surface and take a deep breath before diving on full inspiration. This breathing pattern suggests that the lung is used as an O2 store during diving.
Buccopharyngeal pumping is the gaseous exchange that occurs when water enters the mouth of the turtle, and the specialized membrane structure in the mouth absorbs water.
A unique oxygen exchange in snapping turtles is the cloacal breathing through the cloaca, which is an opening at the rear end of the animal. In snapping turtles, it accounts for 5- 31% of the oxygen supply.
Cloaca, the multi-purpose chamber
“Breathing through the butt” – catchy phrase, but turtles actually do use their but for breathing.
The cloaca is a chamber under the turtle’s tail that carries unique functions – excretion of urine and feces, release of sperm and eggs, copulation, and respiration. The cloaca ends in a vent through which respiration, reproduction, and excretion occur.
Some turtles, such as snapping turtles, have two sac-like extensions on the sides of the cloaca called bursae, lined with tiny finger-like villi with blood vessels that can exchange oxygen and carbon dioxide between the bloodstream and the water. As the turtle pushes water through its cloaca, the lining absorbs dissolved oxygen from the water into the bloodstream, and carbon dioxide passes from the blood to the outside.
Brumation for an anaerobic lifestyle
Brumation is a synonym for hibernation in mammals. During this period, turtles don’t require much oxygen and switch to anaerobic respiration. Brumating turtles such as snappers and painted turtles avoid lactic acid buildup by using calcium and carbonates from their skeletons and shells to buffer the acid.
Conclusion
Amphibians! Make way for the turtles for their complex respiratory system. Turtles have evolutionarily devised many mechanisms to stay underwater without using their lungs. In addition to pulmonary respiration, turtles possess buccopharyngeal respiration and cloacal respiration. They also use the lungs as a storage space for oxygen and can shift to anaerobic respiration to save oxygen. Take a deep breath to live long like a turtle.
References
Druzisky, K.A., and Brainerd, E.L.Buccal oscillation and lung ventilation in a semi-aquatic turtle, Platysternon megacephalum.
Druzisky-Brainerd-2001-Zool.pdf (brown.edu)
The secret to turtle hibernation: Butt-breathing | PBS NewsHour, Nov 26, 2017.
https://www.pbs.org/newshour/science/the-secret-to-turtle-hibernation-butt-breathing
Jackson, D. Hibernating without oxygen: physiological adaptations of the painted turtle. J Physiol. 2002 Sep 15; 543(Pt 3): 731–737. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2290531/
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