Figure 418

to transmit at the same time collateral impulses into the brain stem to excite the respiratory center. This is analogous to the stimulation of the vasomotor center of the brain stem during exercise that causes a simultaneous increase in arterial pressure.

Actually, when a person begins to exercise, a large share of the total increase in ventilation begins immediately on initiation of the exercise, before any blood chemicals have had time to change. It is likely that most of the increase in respiration results from neuro-genic signals transmitted directly into the brain stem respiratory center at the same time that signals go to the body muscles to cause muscle contraction.

Interrelation Between Chemical Factors and Nervous: Factors in the Control of Respiration During Exercise. When a person exercises, direct nervous signals presumably stimulate the respiratory center almost the proper amount to supply the extra oxygen required for exercise and to blow off extra carbon dioxide. Occasionally, however, the nervous respiratory control signals are either too strong or too weak. Then chemical factors play a significant role in bringing about the final adjustment of respiration required to keep the oxygen, carbon dioxide, and hydrogen ion concentrations of the body fluids as nearly normal as possible. This is demonstrated in Figure 4l-9, which shows in the lower curve changes in alveolar ventilation during a 1-minute period of exercise and in the upper curve changes in arterial Pco2. Note that at the onset of exercise, the alveolar ventilation increases instantaneously, without an initial increase in arterial Pco2. In fact, this

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Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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