Physiological Function during Exercise and Environmental Stress in Humans—An Integrative View of Body Systems and Homeostasis

Abstract

Claude Bernard’s milieu intérieur (internal environment) and the associated concept of homeostasis are fundamental to the understanding of the physiological responses to exercise and environmental stress. Maintenance of cellular homeostasis is thought to happen during exercise through the precise matching of cellular energetic demand and supply, and the production and clearance of metabolic by-products. The mind-boggling number of molecular and cellular pathways and the host of tissues and organ systems involved in the processes sustaining locomotion, however, necessitate an integrative examination of the body’s physiological systems. This integrative approach can be used to identify whether function and cellular homeostasis are maintained or compromised during exercise. In this review, we discuss the responses of the human brain, the lungs, the heart, and the skeletal muscles to the varying physiological demands of exercise and environmental stress. Multiple alterations in physiological function and differential homeostatic adjustments occur when people undertake strenuous exercise with and without thermal stress. These adjustments can include: hyperthermia; hyperventilation; cardiovascular strain with restrictions in brain, muscle, skin and visceral organs blood flow; greater reliance on muscle glycogen and cellular metabolism; alterations in neural activity; and, in some conditions, compromised muscle metabolism and aerobic capacity. Oxygen supply to the human brain is also blunted during intense exercise, but global cerebral metabolism and central neural drive are preserved or enhanced. In contrast to the strain seen during severe exercise and environmental stress, a steady state is maintained when humans exercise at intensities and in environmental conditions that require a small fraction of the functional capacity. The impact of exercise and environmental stress upon whole-body functions and homeostasis therefore depends on the functional needs and differs across organ systems.

Exertional heat stroke: pathophysiology and risk factors

“…Important gaps in knowledge include the contributions of sex hormones to EHS susceptibility, whether dehydration is a risk factor for EHS, the role of endotoxemia in nonlethal EHS pathophysiology, the time course of changes in coagulofibrinolytic markers in EHS, and the impact of oral contraceptives on EHS risk. Research studies partitioning the contributions of different physiological systems 131 and risk factors to EHS are required to advance knowledge on the precise sequence of events leading to EHS and the underlying mechanisms mediating organ damage.…”

Innate Immunity in Cardiovascular Diseases – Identification of Novel Molecular Players and Targets

“…The adverse effect of psychological stress upon various human diseases has been well known since decades [240][241][242] and several stress-induced brain -immune system interactions have been elucidated at cellular and molecular level [241,264]. It is also obvious that stress reduction is highly desirable with regard to cardiovascular diseases [265][266][267][268], although often difficult to achieve in everyday life or the clinical setting. Any new avenue arising from recent neuroimmune research would be most welcome, of course.…”

Innate Immunity in Cardiovascular Diseases – Identification of Novel Molecular Players and Targets

“…The adverse effect of psychological stress upon various human diseases has been well known since decades [214][215][216] and several stress-induced brain -immune system interactions have been elucidated at cellular and molecular level [215,237]. It is also obvious that stress reduction is highly desirable with regard to cardiovascular diseases [238][239][240][241], although often difficult to achieve in everyday life or the clinical setting. Any new avenue arising from recent neuroimmune research would be most welcome, of course.…”