Hemoglobin carries oxygen and transports it throughout the body (Wikipedia 2005). To bind to hemoglobin and form oxyhemoglobin, oxygen must diffuse from air into the lungs. Oxygen partial pressure substantially affects diffusion into the lungs. Low oxygen partial pressure due to hypobaria greatly hinders diffusion, and therefore reduces formation of oxyhemoglobin (Duncan 2005). Reduced oxyhemoglobin results in hypoxia, a state of inadequate oxygen supply (Wikipedia 2005). The oxyhemoglobin dissociation curve depicts the relationship between oxygen diffusion and ambient oxygen partial pressure (Oxyhemoglobin Dissociation Curve 2005). As oxygen partial pressure decreases, hemoglobin affinity (represented by % oxygen saturation) is remarkably reduced. Therefore, available oxygen dramatically decreases at high altitudes, often resulting in hypobaric hypoxia.

Figure 1.Oxyhemoglobin dissociation curve (Oxyhemoglobin Dissociation Curve 2005). Image adapted from http://perfline.com/notebook/curve.html.

Even in environments with very low oxygen partial pressure, hypoxia can be resisted. Through physiological adaptations that greatly enhance hemoglobin affinity, % oxygen saturation, diffusion rates and other respiratory and circulatory functions, the state of inadequate oxygen supply can be avoided. Hummingbirds are capable of resisting hypoxia at high altitudes, and can therefore survive and flourish at high elevations.

This website was created by Carrie Black as a part of a class project in the Animal Physiology Class at Davidson College.

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