Space Physiology Quiz

Space Physiology: Adapting to Extreme Environments

• The human body can adapt to a wide range of conditions, from the depths of the ocean to the Himalayas and even space.
• The extreme environment of space poses unique medical challenges due to prolonged exposure to acceleration forces, radiation, and weightlessness.
• The absence of a static gravitational field and a protective atmosphere in space highlights the importance of gravity in sustaining life on Earth.
• Early space missions like Skylab (1970s) revealed negative calcium balance with bone density loss, muscle atrophy, cardiovascular and hematological changes, metabolic and endocrine disturbances, and sleep disruptions.
• These changes were similar to those observed in aging populations on Earth.
• Most satellites operate in low Earth orbit (LEO), an altitude above 200 km and below 2000 km.
• In LEO, objects are subjected to about 90% of Earth's gravity, but orbital speed counterbalances gravity creating a free-falling state and apparent weightlessness.
• Radiation exposure outside the atmosphere is a significant concern, as the atmosphere protects us from heavy ions and proton fluxes that bombard Earth.

Cardiovascular Effects

• Gravity plays a crucial role in fluid distribution, influencing the evolution of the cardiovascular system.
• On Earth, fluids shift based on gravity, leading to a higher mean blood pressure (BP) in the feet compared to the head in upright posture.
• In space, this gradient doesn't occur, causing a redistribution of blood towards the head, impacting baroreceptors, the nervous and endocrine systems.
• Within minutes of entering microgravity, astronauts experience "space motion sickness," characterized by nausea, vomiting, headache, fatigue, and loss of appetite.
• This "space motion sickness" is caused by altered sensory input from the vestibular system, creating a mismatch between expected and actual sensory vestibular inputs during movement.
• The unloading of otolith organs in the first few days of microgravity exposure contributes to motion sickness, which typically subsides around day 5.
• "Puffy Head, Chicken Legs" condition occurs in the initial hours and days of exposure to microgravity, where blood shifts to the head and chest, leading to swelling.
• In microgravity, the heart requires less contractility to send blood to the head, resulting in atrophy (−8 to −10%) after 10 days of spaceflight.
• To compensate for blood redistribution in early stages, the body reduces heart rate, lowers thirst, and increases urine output to manage blood volume changes.
• After acclimatization, astronauts experience a reduced total blood volume (increased hematocrit), while maintaining pre-flight levels of mean arterial pressure and heart rate.

Musculoskeletal Effects

• Prolonged exposure to microgravity affects the musculoskeletal system, leading to bone and muscle mass loss.
• Reduced use and perfusion changes contribute to bone and muscle loss.
• The rate of bone mineral density loss during a 6-month ISS stay is comparable to that of a person aging from 50 to 60 on Earth.
• Bone mineral loss is higher in weight-bearing sites like the lumbar spine, femoral neck, and trochanter, pelvis, calcaneus, and leg, while arm bones are less affected.
• Muscles are crucial for movement and counteracting gravity, requiring regular use for maintaining structure and function.
• In microgravity, the lack of gravity support leads to atrophied antigravity muscles.
• Different durations of microgravity exposure result in varying degrees of muscle loss.
• These physiological alterations can impact rehabilitation post-injury, especially in aging individuals. Therefore, it is crucial to focus on muscle groups more prone to loss due to unloading or sedentary behavior.