BOX 2–1 Some Major Human Physiological Changes Resulting from Extended Travel in Earth Orbit

Musculoskeletal System

Loss of bone mineral density

Loss of skeletal muscle

Cardiovascular System

Orthostatic hypotension

Loss of hydrostatic pressure

Pulmonary System

Changes in pulmonary circulation and gas exchange

Alimentary System


Decrease in absorption or malabsorption

Nervous System


Motion sickness

Disturbed fine motor and gross motor functions

Altered sleep-circadian rhythm and sleep deprivation

Reproductive System

Effects of radiation on gametes

Urinary System

Renal calculi

Hematological and Immunological Systems


Potential immunologic depression

Source: Billica, 2000.

are by no means exhaustive, however. The material in this chapter is arranged by organ system, with those for which the physiological effects are best documented presented first. The chapter also includes a discussion of future methods for the monitoring of astronauts’ health status—an important aspect of detecting, understanding, and countering the untoward physiological changes that may affect astronaut well-being and mission performance.

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