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INTRODUCTION TO THE NOMENCLATURE OF BIOLOGICAL CHANGE

Learning Objectives

  • The student will be able to describe the effects of cold, hot, and humid environments on the patterns of ventilation.

  • The student will be able to define cardiovascular drift and the experimental approach that is used to measure it.

  • The student will be able to enumerate changes in lung function after acute exposures to particulates, ozone, and other constituents of smog.

  • The student will be able to identify the changes in arterial blood gases, hyperventilation, and red cell mass with acute or chronic high altitude exposure.

  • The student will be able to explain the pulmonary physiology associated with breath-hold diving and deeper submersions using scuba gear.

Lung tissues and the processes of respiration are stressed when exposed to the extreme environments that humans inhabit. Although detailed discussions of each such environment are beyond the scope of this book, there are general respiratory responses that reflect the system's adaptability over time, age, and level of aerobic capacity (Chap. 12). Situations that induce the most relevant adaptations include: cold, hot, and humid environments; regions with significant and persistent air pollution; short and long-term life at high altitude; and submersion under water using breath-holding or compressed air such as scuba diving gear. Each of these will be discussed here.

For clarity, this chapter recognizes three levels of organismal response to changing environmental conditions. Acclimation is a suite of responses induced in an organism by a single changed factor (like temperature, water supply, or light/dark cycle), usually in a laboratory setting where all other known variables are controlled. Periods of acclimation rarely last more than 2 months and involve individual organisms. For example, after spending a year living next to the airport you may barely hear its noise, but friends do not like to sleep over. Once you have moved away for a year, you will not sleep well at your old place either. Acclimations are transient and reversible.

Acclimatization is a more complex suite of responses by an organism to natural, multifactorial changes in the environment, perhaps encountered seasonally or when migrating across biomes. To achieve its full potential in the organism, acclimatization must optimize rapidly enough to yield benefits within one lifetime; fur density and lipid deposition only improve survival in the winter if they are in place by fall. Acclimatization usually involves at least a familial bloodline or other closely aligned group. Importantly too, larger groups undergoing acclimatization simultaneously have a higher likelihood of their changes enduring in the population. For example, families that bicycle or run regularly together often have similar body phenotypes. They are manipulating common pressure points within their similar genotypic backgrounds to affect more durable change within their own lifetimes. Any reader who owns animals in a temperate climate is familiar with their seasonal changes in girth, fur length, and breeding behaviors.

Knowing this, adaptation in a ...

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