Space Mission and Bone Health

Introduction

• March 2015: Astronauts Scott Kelly (USA) and Mikhail Kornienko (Russia) began a one-year mission on the ISS.
• Longest tour of duty on the International Space Station (ISS).
• Primary concern: Physical effects of prolonged microgravity.

Microgravity and its Effects

• Microgravity impact:
  • Trouble sleeping
  • Puffy faces
  • Loss of muscle mass
  • Serious damage to bones
• Bones are active, dynamic connective tissues, constantly regenerating and repairing.
• Functions of bones include:
  • Structural support
  • Storage of minerals (calcium, phosphate)
  • Blood cell production in bone marrow
  • Energy storage as fat
  • Homeostasis regulation via blood calcium levels and osteocalcin hormone

Bone Loss in Space

• Astronauts in microgravity suffer 1-2% bone loss per month.
• Comparatively, elderly people lose 1-2% bone mass per year.
• Scott and Mikhail could lose up to 20% bone mass in a year.
• Most bone loss is reversible but requires years of rehabilitation.

Importance of Bones

• Human body has 206 bones.
• Division of bones:
  • Axial bones: Skull, vertebral column, rib cage
  • Appendicular bones: Limbs, pelvis, shoulder blades
• Types of bones by shape:
  • Long bones (e.g., femur, tibia)
  • Short bones (e.g., talus, wrist bones)
  • Flat bones (e.g., sternum, scapulae)
  • Irregular bones (e.g., vertebrae, pelvis)
• Bone structure:
  • Compact (cortical) bone: Dense external layer
  • Spongy bone: Porous, contains bone marrow (red and yellow)

Microanatomy of Bones

• Osteons: Cylindrical, weight-bearing structures
• Lamellae: Concentric tubes within osteons
• Central canals: Hold nerves and blood vessels
• Lacunae: Tiny spaces housing osteocytes (mature bone cells)

Bone Remodeling

• Bone remodeling process managed by osteocytes, osteoblasts, and osteoclasts.
• Osteocytes: Sense stress/strain, signal for repair.
• Osteoblasts: Bone-building cells, secrete collagen and minerals.
• Osteoclasts: Bone-resorbing cells, break down bone tissue.
• Remodeling steps:
  • Osteocytes detect damage, signal osteoclasts.
  • Osteoclasts resorb damaged bone, release minerals into blood.
  • Osteoclasts self-destruct (apoptosis) after resorption.
  • Osteoblasts rebuild bone by laying down new tissue.

Impact of Microgravity on Bone Remodeling

• In microgravity:
  • Osteocytes receive less mechanical loading stimuli.
  • Osteoclasts increase bone resorption rate.
  • Osteoblasts reduce bone formation.
• Result: Imbalance leads to significant bone loss.

Conclusion

• Challenges of long-term space missions include preventing significant bone loss.
• Summary of skeletal system anatomy, bone microanatomy, and remodeling processes.

Credits

• Episode production details and acknowledgments.