How does a hopping kangaroo breathe?

We developed a model to demonstrate how a hopping kangaroo breathes. Interestingly, a kangaroo uses less energy to breathe while hopping than while standing still. This occurs, in part, because rather than using muscle power to move air into and out of the lungs, air is pulled into (inspiration) and pushed out of (expiration) the lungs as the abdominal organs "flop" within the kangaroo's body. Specifically, as the kangaroo hops upward, the abdominal organs lag behind, and the insertion of the diaphragm is pulled toward its origin, flattening the dome and increasing the vertical dimension of the thoracic cavity (the thoracic cavity and lungs enlarge). Increasing the volume of the thoracic cavity reduces alveolar pressure below atmospheric pressure (barometric pressure), and air moves into the alveoli by bulk flow. In contrast, the impact of the organs against the diaphragm at each landing causes expiration. Specifically, upon landing, the abdominal organs flop into the diaphragm, causing it to return to its dome shape and decreasing the vertical dimension of the thoracic cavity. This compresses the alveolar gas volume and elevates alveolar pressure above barometric pressure, so air is expelled. To demonstrate this phenomenon, the plunger of a syringe model of the respiratory system was inserted through a compression spring. Holding the syringe and pressing the plunger firmly against a hard surface expels air from the lungs (the balloon within the syringe deflates) and compresses the spring. This models the kangaroo landing after a hop forward. Subsequently, the compression spring provides the energy for the "kangaroo" to "hop" forward upon the release of the syringe, and air enters the lungs (the balloon within the syringe inflates). The model accurately reflects how a hopping kangaroo breathes. A model was chosen to demonstrate this phenomenon because models engage and inspire students as well as significantly enhance student understanding.     

How do avian embryos breathe? Oxygen transport in the blood of early chick embryos

1. Chick embryos with primary circulation, up to about 3 days of development, show no hemoglobin-mediated transport of oxygen. 2. In embryos with secondary circulation, between 3 and 6 days of incubation, the vascular area acts as the respiratory organ. Its efficiency in the oxygen uptake is less than that of the chorioallantois of later embryos. On the contrary, oxygen release to the tissues is highly efficient. 3. A full efficient hematic uptake of oxygen is reached at about the 6th incubation day, when chorioallantois acts as the embryonic respiratory organ. 4. The different respiratory mechanisms of developing chick embryo are closely related to the functional properties of the various hemoglobins which are produced during the embryonic life.     

Energetics of the smallest: Do bacteria breathe at the same rate as whales?

Power laws describing the dependence of metabolic rate on body mass have been established for many taxa, but not for prokaryotes, despite the ecological dominance of the smallest living beings. Our analysis of 80 prokaryote species with cell volumes ranging more than 1,000,000-fold revealed no significant relationship between mass-specific metabolic rate q and cell mass. By absolute values, mean endogenous mass-specific metabolic rates of non-growing bacteria are similar to basal rates of eukaryote unicells, terrestrial arthropods and mammals. Maximum mass-specific metabolic rates displayed by growing bacteria are close to the record tissue-specific metabolic rates of insects, amphibia, birds and mammals. Minimum mass-specific metabolic rates of prokaryotes coincide with those of larger organisms in various energy-saving regimes: sit-and-wait strategists in arthropods, poikilotherms surviving anoxia, hibernating mammals. These observations suggest a size-independent value around which the mass-specific metabolic rates vary bounded by universal upper and lower limits in all body size intervals.     

How does the eye breathe? Evidence for neuroglobin-mediated oxygen supply in the mammalian retina

Visual performance of the vertebrate eye requires large amounts of oxygen, and thus the retina is one of the highest oxygen-consuming tissues of the body. Here we show that neuroglobin, a neuron-specific respiratory protein distantly related to hemoglobin and myoglobin, is present at high amounts in the mouse retina (approximately 100 microm). The estimated concentration of neuroglobin in the retina is thus about 100-fold higher than in the brain and is in the same range as that of myoglobin in the muscle. Neuroglobin is expressed in all neurons of the retina but not in the retinal pigment epithelium. Neuroglobin mRNA was detected in the perikarya of the nuclear and ganglion layers of the neuronal retina, whereas the protein was present mainly in the plexiform layers and in the ellipsoid region of photoreceptor inner segment. The distribution of neuroglobin correlates with the subcellular localization of mitochondria and with the relative oxygen demands, as the plexiform layers and the inner segment consume most of the retinal oxygen. These findings suggest that neuroglobin supplies oxygen to the retina, similar to myoglobin in the myocardium and the skeletal muscle.