Lecture on Astronauts and Bone Health in Space

Introduction

• Mission: In March 2015, American astronaut Scott Kelly and Russian colleague Mikhail Kornienko began a one-year mission aboard the ISS.
• Concerns: Includes practical questions (clothing, hygiene, food) and health concerns (physical effects of microgravity).

Physical Effects of Microgravity

• Short-term Symptoms: Trouble sleeping, puffy faces, loss of muscle mass.
• Serious Damage: Bone deterioration.

Bone Function and Structure

• Bone Dynamics: Bones are active tissues, continually breaking down and regenerating.
• Functions: Support, movement, storing minerals, blood cell production (hematopoiesis), energy storage, homeostasis.
• Bone Loss in Space: 1-2% bone loss per month compared to 1-2% per year in elderly on Earth.

Bone Anatomy

• Axial vs Appendicular: Axial (skull, vertebral column, rib cage) for support and protection. Appendicular (limbs, pelvis, shoulder blades) for movement.
• Bone Classification by Shape:
  • Long Bones: Longer than wide (e.g., tibia, fibula, fingers).
  • Short Bones: Cube-shaped (e.g., talus, cuboid, wrist bones).
  • Flat Bones: Thin (e.g., sternum, scapulae).
  • Irregular Bones: Specialized shapes (e.g., vertebrae, pelvis).

Bone Tissue Structure

• Compact Bone: Dense and smooth outer layer.
• Spongy Bone: Porous, with trabeculae. Contains bone marrow.
• Bone Marrow:
  • Red Marrow: Produces blood cells.
  • Yellow Marrow: Stores fat.
• Bone Structure Variations: Differences in distribution of compact and spongy bone among long, short, flat, and irregular bones.

Microanatomy of Bones

• Osteons: Basic structural units with concentric lamellae for strength against torsion.
• Central Canals: Contain blood vessels and nerves.
• Lacunae: Spaces housing osteocytes (mature bone cells).
• Osteocytes: Monitor and maintain bone matrix.
• Osteoblasts and Osteoclasts:
  • Osteoblasts: Bone-building cells.
  • Osteoclasts: Bone-resorbing cells.

Bone Remodeling Process

• Initiation: Osteocytes detect stress/strain and signal for repair.
• Resorption: Osteoclasts break down old bone tissue.
• Formation: Osteoblasts rebuild bone tissue.
• Balance: Continuous cycle of breakdown and formation maintains bone health.

Challenges in Space

• Exercise: Essential but insufficient to fully prevent bone density loss.
• Microgravity Effects: Increased osteoclast activity and decreased osteoblast activity lead to significant bone loss.
• Solutions Needed: Addressing bone health along with other vital needs (oxygen, food, mental stability).

Conclusion

• Summary: Anatomy and functions of bones, bone microanatomy, and the bone remodeling process.
• Acknowledgments: Thanks to patrons and contributors to Crash Course.

Additional Information

• Crash Course Credits: Acknowledgments to writers, editors, consultants, and production team members.