Lecture Notes: The Skeletal System and Space Exploration
Overview
American astronaut Scott Kelly and Russian cosmonaut Mikhail Kornienko embarked on a year-long mission aboard the International Space Station (ISS) in March 2015.
The mission aimed to study the physical effects of prolonged exposure to microgravity.
Concerns of Space Travel
Key Concerns:
Physical effects: Difficulty walking post-mission due to microgravity’s impact on the body.
Microgravity-related issues: Trouble sleeping, puffy faces, muscle mass loss, and bone density reduction.
Bone Dynamics
Bone Characteristics:
Bones are dynamic, living tissues.
Functions include storage of calcium and phosphate, blood cell production (hematopoiesis), energy storage as fat, and maintaining homeostasis.
Bone Regeneration:
Skeleton is renewed approximately every 7-10 years.
Impact of Microgravity on Bones
Bone Loss in Space:
Astronauts can lose 1-2% of bone mass each month in space, compared to 1-2% per year in elderly on Earth.
Prolonged exposure can result in significant bone loss, requiring years of rehabilitation.
Bone Structure and Classification
Human body has 206 bones.
Axial vs. Appendicular Bones:
Axial: Skull, vertebral column, rib cage (foundation and protection).
Appendicular: Limbs and girdles for movement.
Bone Types by Shape:
Long bones (e.g., femur, tibia).
Short bones (e.g., carpals).
Flat bones (e.g., scapula).
Irregular bones (e.g., vertebrae).
Microanatomy of Bones
Bone Composition:
External layer: Compact/cortical bone.
Internal layer: Spongy bone with trabeculae and bone marrow.
Bone Marrow:
Red marrow: Blood cell production.
Yellow marrow: Fat storage.
Structural Units:
Osteons: Cylindrical structures forming the bone matrix.
Lamellae: Concentric tubes with alternating collagen fibers.
Bone Remodeling Process
Cell Types Involved:
Osteocytes: Monitor bone matrix and signal remodeling.
Osteoblasts: Bone-building cells, secrete collagen and enzymes.
Osteoclasts: Bone-resorbing cells, break down old bone.
Remodeling Steps:
Osteocytes detect damage and signal osteoclasts.
Osteoclasts resorb old bone, making way for osteoblasts to rebuild.
Balance between osteoclast activity (resorption) and osteoblast activity (formation) critical.
Space Mission Implications
Space crews exercise 15 hours a week to combat bone density loss.
In microgravity, osteoclast activity increases while osteoblast activity decreases, leading to imbalance.
Maintaining astronaut health involves addressing bone mass preservation in space environment.
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