Bone Tissue Growth and Skeletal Functions

Bone Tissue Growth and Development

• Bone is a dynamic, metabolically active tissue, crucial for stature (approximately 98% of it) and comprising ~15% of infant weight, ~17% in adults, and ~14% in older adults.
• Bone is a composite material, a mixture of strong but brittle components (like glass) and flexible but less strong polymers (like plastic). This composite structure gives bone both strength and flexibility.
• Its tensile strength equals cast iron, yet bone is significantly lighter and more flexible.

Functions of the Skeletal System

• Protection: Bones shield vital organs.
• Support: The skeleton provides a framework that supports soft tissues and organs.
• Locomotion: Bones act as attachment points for muscles, enabling limb movement.
• Blood Cell Production: Bone marrow within long and flat bones produces red blood cells, white blood cells, and platelets.
• Mineral Reservoir: Bones store 99% of the body's calcium and 85% of the phosphorus.
• Mineral Trap: Bones trap harmful minerals like lead.

Bone Classification

• Long Bones: Femur, tibia, radius
• Short Bones: Bones in the hands and feet (specifically 27 bones located within the hand and wrist)
• Irregular Bones: Vertebrae
• Flat Bones: Skull, clavicle, mandible, scapula

Bone Tissue Types

• Cortical (Compact) Bone: Dense, solid bone forming the outer shell (periosteum).
• Trabecular (Cancellous) Bone: Spongy, lattice-like inner scaffolding (endosteum).

Bone Modeling and Remodeling

• Modeling: The primary process during growth, adding bone without resorption, altering bone shape and mass in response to loads.
• Remodeling: The primary process during adulthood, replacing fatigued or damaged bone with new bone tissue;a continuous process of bone resorption and formation. This process involves osteoclasts breaking down old bone, and osteoblasts building new bone, usually taking 3-6 months
• Modelling and remodeling allow the skeleton to adapt to changes in mechanical stressors. Microfractures from everyday activity are routinely repaired.

Bone Loss Over Time

• Bone is constantly undergoing formation and resorption.
• After growth ceases, the body's net bone loss begins to exceed the gain.

Bone Health and Prevention

• Peak Bone Mass: Building peak bone mass during youth is crucial. Approximately 22% of adult bone mass is accrued during approximately one year, or at least within one year, from the perimenstrual phase of their development.
• Physical Activity: Regular weight-bearing exercise, especially during growth, is highly beneficial in maximizing bone density and structure. A lack of loading/inactivity is detrimental to the skeleton. Exercise's effects are better when commenced before or around puberty.

Osteoporosis

• Definition: A metabolic bone disorder with low bone mass and micro-architectural deterioration, leaving bones fragile.
• Symptoms: Asymptomatic; fractures often trigger diagnosis (hips, wrists, vertebrae).
• Prevention: Maximizing peak bone mass during growth, delaying bone loss, and reducing the rate of loss. This can be achieved with a good diet and regular weight-bearing exercise.

Dual-energy X-ray Absorptiometry (DXA)

• Are bone mineral density (BMD): used as a predictor of fracture risk, especially hip fractures. A 10% decline in aBMD more than doubles your fracture risk.

Impact of Bed Rest on Bone

• Prolonged bed rest can significantly decrease bone mineral density, often at a rate of approximately 1% per week in weight-bearing areas.

Athletes vs. Non-Athletes

• Athletes demonstrate higher bone mineral density (BMD) at the hip and spine compared to non-athletes. This effect is particularly impactful when exercise begins during childhood.