Various turtles spend large amounts of their lives underwater or underground. All turtles and tortoises breathe air and must surface at regular intervals to refill their lungs. The turtles can take up dissolved oxygen from the water using these papillae, in much the same way that fish use gills to respire.
The trachea splits near the heart into two bronchi that deliver air to the lungs, where it is absorbed into the body.
Since a turtle’s shell cannot expand and contract the way a person’s ribs do, turtles have muscles inside their shells that expand and contract to move air in and out of the lungs.
Not only can turtles actively breathe oxygen into their lungs, similar to humans, but all aquatic turtles have some ability to extract oxygen from the water in which they live.
One way is through a process called “buccopharyngeal pumping,” or gas exchange.
Buccal pumping is “breathing with one’s cheeks”: a method of ventilation used in respiration in which the animal moves the floor of its mouth in a rhythmic manner that is externally apparent It is the sole means of inflating the lungs in amphibians.
However, another more unusual form of gas exchange occurs at the opposite end of the snapping turtle.
Eastern snapping turtles have specialized cells in their cloaca (an opening used for excretion and reproduction) called cloacal bursae that can extract oxygen from the water. Much like the gas exchange that occurs during buccopharyngeal pumping, oxygen is absorbed by these bursae into the bloodstream.
Although unusual, it appears that this aquatic respiration is limited in snapping turtles. Added. buccopharyngeal pumping and/or cloacal respiration accounts for anywhere between five and 31 percent of a snapping turtle’s oxygen consumption, depending on water temperature and environmental factors.
In contrast, the Fitzroy River turtle (Rheodytes leukops) in Australia can use cloacal respiration to obtain a large portion, if not all, of its oxygen.
Respiring through their multi-purpose rear end provides these turtles with a breath of not-so-fresh air.
The respiratory system of the turtle is modified to accommodate some peculiar morphological features. Notice the trachea, which has become elongated in response to the posterior migration of the heart and viscera and, in part, to the extendable neck.
The shell of the turtle poses a special problem in the ventilation of the lungs. The rigidity of the shell prevents the use of the ribs in the aspiration pump.
Alternatively, turtles possess sheets of muscle within the shell that, through contraction and relaxation, force air in and out of the lungs. In addition, turtles can alter the pressure within the lungs by moving the limbs in and out of the shell
The blood oxygen level of a painted turtle that has submerged for over three months drops to zero.
Incorporation of the ribs into the turtle shell negates the costal movements that affect lung ventilation in other air-breathing amniotes. Instead, turtles have a unique abdominal-muscle-based ventilatory apparatus whose evolutionary origins have remained mysterious.
Normal ventilation is impossible in turtles because their intercostal muscles are lost during embryogenesis and their ribs are bound in a typically rigid shell. Instead, turtles employ a unique apparatus mainly involving two paired, antagonistic abdominal (hypaxial) muscles: Musculus transversus.
During normal respiration, the mouth is held closed and air enters through the nostrils which appear to be always open and lack valves.
The nares open into the dorsal part of the buccal cavity immediately dorsal to the tongue, behind which lies the slit-like glottis.
Not all turtles and tortoise shells are the same!?!?
The lungs of Testudo are limited by, and attached to, a rigid box on three sides; lung patency is thus assured and only the ventral diaphragmatic membrane is free to move.
Sea turtles have subdivided, multicameral lungs with reinforced large diameter airways and homogeneously distributed parenchyma containing smooth muscle and fibrous connective tissue.
These structural features allow high respiratory flows. In addition, the vital capacity (VC) in marine mammals and sea turtles is almost as large as the total lung capacity (TLC). Thus, these animals can exchange almost the entire lung volume in a single breath.
However, unlike marine mammals, the current knowledge suggests that the turtle lungs are the major O2 store instead of the blood. Loggerhead sea turtles are reported to expire when surfacing and breath before they dive on full inspiration. This breathing pattern suggests that the lung is used as an O2 store during diving.
What Happens Once They Are Holding Their Breath?
One deep breath may last a turtle several hours. Some freshwater turtles can remain underwater for several days (except during hibernation, when they can remain underwater for several months).
They do this by lying still on the bottom, thereby using up very little oxygen. Some species can even take a little oxygen from the water, as a fish does, by using specialized body tissues.
In climates where the ground and water freeze in winter, turtles survive the cold by hibernating. They may burrow in the muddy bottoms of ponds or streams or crawl under decaying vegetation.
When a turtle hibernates or brumates, it uses up very little oxygen. Even if it spends months underwater, a hibernating turtle does not have to come up for air. Its body does not have the same oxygen needs that it has when the turtle is active during the warmer months.
When muscle is starved for oxygen, it produces lactic acid, which causes muscle cramps and weakness. Hibernating some species such as snappers and painted turtles avoid lactic acid buildup by using calcium and carbonates from their skeletons and shells to buffer the acid.
Even though their systems have all but shut down, turtles can still discern changes in light intensity that may signal the spring ice melt, and with it, the chance to surface and fill their lungs.
Acidosis?!?
Anoxic turtles accumulate high levels of lactate in the blood. To avoid fatal acidosis, turtles exploit buffer reserves in their large mineralized shell.
The shell acts by releasing calcium and magnesium carbonates and by storing and buffering lactic acid. Together with profound metabolic depression, shell buffering permits survival without oxygen for several months at 3 degrees C.
