Bone disorders result from abnormal bone deposition and resorption (clinical)

Osteomalacia

Poor bone mineralization; calcium salts aren't adequately deposited, leaving bones soft and weak.

Main Symptom of Osteomalacia

Bone pain when weight is placed on affected bones.

Rickets

Childhood form of osteomalacia; causes severe bone weakness and deformities during growth.

Signs of Rickets

Bowed legs, skeletal deformities, enlarged long-bone ends, and widened growth plates.

Causes of Osteomalacia and Rickets

Insufficient dietary calcium or vitamin D deficiency.

Treatment and Prevention

Increase vitamin D intake and get sunlight exposure to help the body produce vitamin D.

Osteoporosis

Disorder where bone resorption exceeds bone deposition, causing bone mass to decrease.

What Happens to Bones in Osteoporosis?

Bone matrix remains normal, but bones become porous, lighter, and fragile.

Who Is Most Commonly Affected by Osteoporosis?

Postmenopausal females; about 1 in 3 females over 50 worldwide experience an osteoporosis-related fracture.

Common Osteoporosis Fractures

Compression fractures of the vertebrae and fractures of the femoral neck (hip fractures).

Hormonal Risk Factors

Low estrogen or androgen levels reduce bone deposition and allow more bone resorption. Menopause greatly increases risk.

Lifestyle and Dietary Risk Factors

Low body weight, insufficient weight-bearing exercise, poor calcium/vitamin D/protein intake, and smoking.

Other Risk Factors

Family history, diabetes, hyperthyroidism, alcohol consumption, and certain medications (steroids and some cancer drugs).

Preventing Osteoporosis

Reduce controllable risk factors, such as smoking, poor nutrition, and lack of weight-bearing exercise.

Treating Osteoporosis

Weight bearing exercise, adequate calcium and vitamin D, and medications that reduce osteoclast activity.

Paget's Disease

Disorder involving excessive, disorganized bone deposition and resorption.

Pagetic Bone

Newly formed bone that is poorly organized, has more spongy than compact bone, and is weak due to reduced mineralization.

What Happens as Paget's Disease Progresses?

Osteoclast activity decreases while osteoblasts continue working, causing irregular bone thickening and possible filling of the medullary cavity.

Common Locations and Symptoms of Paget's Disease

Usually localized to the spine, pelvis, femur, or skull; causes bone deformity and pain.

Cause and Treatment of Paget's Disease

Cause is unknown, but a virus may trigger it. Bisphosphonates and high-dose calcitonin help prevent bone breakdown.

Embryonic Bone Development

he mesoderm germ layer produces mesenchymal cells, which form the membranes and cartilage of the embryonic skeleton.

Ossification

The process of bone formation; embryonic membranes and cartilage gradually become bone.

When Does Ossification Begin?

Most long bones begin ossifying by 8 weeks after conception and have well-developed primary ossification centers by 12 weeks.

Bone Development at Birth

Most long bones are ossified except for their epiphyses.

How Do Long Bones Grow After Birth?

Secondary ossification centers develop, while epiphyseal plates allow bones to lengthen throughout childhood and adolescence.

When Does Skeletal Growth Stop?

By about age 25, nearly all bones are completely ossified and skeletal growth ceases.

Bone Remodeling at Different Ages

Children and adolescents: deposition exceeds resorption. Young adults: balanced. Older adults: resorption exceeds deposition.

Genetics and Bone Density

Genetics strongly influences lifetime bone density and osteoporosis risk, including genes related to vitamin D receptors.

When Does Bone Mass Begin to Decline?

Bone mass begins decreasing around the fourth decade (ages 30–39), except in the bones of the skull.

Why Is Age-Related Bone Loss a Greater Problem for Females?

Males generally have greater skeletal mass than females during young adulthood, giving females less bone mass to lose.

Qualitative Changes in Aging Bones

Less complete osteons and mineralization, reduced blood supply, and slower fracture healing.