Vertebrate Respiration and Circulation in Extreme Conditions


The acquisition and internal transport of respiratory gases and metabolic fuels depend on linked processes, with design and function related to energetic demands and attributes of the environment. Environmental challenges to these processes reflect variation in the density of gases and the pressures that prevail in the environmental medium.

Keywords: respiration; circulation; altitude; diving; hypoxia; gravity

Figure 1.

Schematic illustration of the four steps in the oxygen transport chain (sometimes called the ‘oxygen cascade’) described in the text. (1) Gas exchange. (2) Diffusion into blood. (3) Blood transport of oxygen. (4) Diffusion into tissues. For illustrative purposes, body tissues are represented by three compartments containing mitochondria. In reality, many different tissue compartments are servised by the blood circulation.

Figure 2.

Schematic representation of hypothetical blood columns, illustrating gradients of gravitational pressures depicted by arrows. The size of the arrows corresponds to the magnitude of the pressure vectors. In aquatic environments, pressure outside the blood column increases with depth approximately as do pressures within the blood column. Thus, transmural pressures across the vessel wall remain unchanged along the column length. In aerial environments, the arrows outside the blood column represent atmospheric pressure, which essentially does not change along the length of the column. The wall of the vessel containing the blood is distensible, and therefore increasing gradients of transmural pressure in air cause distension and blood pooling in the lower depths of the blood column. After Lillywhite (1996).

Figure 3.

Relationship between rates of maximal oxygen consumption and altitude for persons who have temporarily adjusted to various altitudes. The data are from a scientific Himalayan expedition and reflect maximal exercise capacities. After Hlastala and Berger (1996).


Further Reading

Ar A (1993) Gas exchange of the avian embryo at altitude – the half‐empty glass. Funktionsanalyse Biologischer Systeme 23: 339–350.

Hlastala MP and Berger AJ (1996) Physiology of Respiration. New York: Oxford University Press.

Hochachka PW, Buck LT, Doll CJ and Land SC (1996) Unifying theory of hypoxia tolerance: molecular/metabolic defense and rescue mechanisms for surviving oxygen lack. Proceedings of the National Academy of Sciences of the USA 93: 9493–9498.

Kooyman GL (1989) Diverse Divers: Physiology and Behaviour. Berlin: Springer‐Verlag.

Kooyman GL and Ponganis PJ (1997) The challenges of diving to depth. American Scientist 85: 530–539.

Lillywhite HB (1996) Gravity, blood circulation, and the adaptation of form and function in lower vertebrates. Journal of Experimental Zoology 275: 217–225.

Mottishaw PD, Thornton SJ and Hochachka PW (1999) The diving response mechanism and its surprising evolutionary path in seals and sea lions. American Zoologist 39: 434–450.

Seymour RS (1978) Gas tensions and blood distribution in sea snakes at surface pressure and at simulated depth. Physiological Zoology 51: 388–407.

Snyder GK (1983) Respiratory adaptations in diving animals. Respiration Physiology 54: 269–294.

West JB (1998) High Life: A History of High‐Altitude Physiology and Medicine. New York: Oxford University Press.

West JB (2000) Human limits for hypoxia: the physiological challenge of climbing Mt. Everest. Annals of the New York Academy of Sciences 899: 15–27.

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Lillywhite, Harvey B(Oct 2001) Vertebrate Respiration and Circulation in Extreme Conditions. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1038/npg.els.0001831]