Bone Growth, Ossification, Remodeling, and Bone Disorders.

Bone remodeling

WHAT: The ongoing process of breaking down old bone and building new bone. FUNCTION: Repairs damage, adapts bone to stress, and helps regulate blood calcium. EXAMPLES: Bone adapting to exercise; replacing old bone tissue.

Wolff's Law

WHAT: Bone changes in response to mechanical stress. FUNCTION: Helps bones adapt to the forces placed on them. EXAMPLES: Weight-bearing exercise can strengthen bones; prolonged bed rest can weaken bones.

Ossification

WHAT: The process of forming bone tissue. FUNCTION: Builds the skeleton during development and replaces or repairs bone. TWO TYPES: Intramembranous and endochondral ossification.

Intramembranous ossification

WHAT: Bone forms directly from connective tissue. FUNCTION: Creates certain bones without first forming a cartilage model. EXAMPLES: Many skull bones; part of the clavicle.

Endochondral ossification

WHAT: Bone forms by replacing a cartilage model. FUNCTION: Forms most bones in the body. EXAMPLES: Femur; humerus.

Osteoid

WHAT: The unmineralized organic matrix produced by osteoblasts. FUNCTION: Provides the framework that later hardens as minerals are deposited. EXAMPLES: Contains collagen fibers; becomes mineralized during bone formation.

Bone resorption

WHAT: The breakdown of bone tissue by osteoclasts. FUNCTION: Removes old bone and releases minerals. EXAMPLES: Normal bone remodeling; helping regulate blood calcium.

What happens when a bone fractures?

Blood vessels break and bleeding occurs. A hematoma forms, inflammation begins, and the body starts repairing the damaged area.

Stage 1 of fracture repair: Hematoma formation

Blood vessels are damaged, causing blood to collect and form a clot at the fracture site. Inflammation begins, and some nearby bone cells may die.

Stage 2 of fracture repair: Fibrocartilaginous callus

A soft callus made of connective tissue and cartilage forms around the break. It helps stabilize the broken bone ends.

Stage 3 of fracture repair: Bony callus

Osteoblasts form new bone, replacing the soft callus with a hard bony callus that connects the broken ends.

Stage 4 of fracture repair: Remodeling

Osteoclasts remove excess bone, while osteoblasts build and reshape bone. The bone gradually regains its shape and strength.

What are the four stages of fracture repair in order?

1. Hematoma formation. 2. Fibrocartilaginous callus formation. 3. Bony callus formation. 4. Bone remodeling.

Difference between a soft callus and a bony callus

A soft callus consists mainly of connective tissue and cartilage. A bony callus consists of new bone tissue.

What do osteoblasts do during fracture repair?

They build new bone matrix and help replace the soft callus with a hard bony callus.

What do osteoclasts do during fracture repair?

They break down and remove bone tissue, helping reshape the bone during remodeling.

Osteoporosis

WHAT: A condition in which bones lose density and become fragile. FUNCTION/IMPACT: Makes bones more likely to fracture. EXAMPLES: Vertebral compression fractures; hip fractures.

Osteomalacia

WHAT: Softening of adult bones, commonly related to inadequate vitamin D or problems with mineralization. IMPACT: Bones may become weak and painful. EXAMPLES: Bone pain; fractures.

Rickets

WHAT: A disorder of growing bones in children, commonly caused by vitamin D deficiency. IMPACT: Bones may not mineralize properly. EXAMPLES: Bowed legs; impaired growth.

Paget disease of bone

WHAT: A disorder involving abnormal bone remodeling. IMPACT: Bone may become enlarged, misshapen, and weaker than normal. EXAMPLES: Pelvis involvement; skull involvement.

Fracture

WHAT: A break or crack in a bone. IMPACT: Disrupts normal bone structure and may damage surrounding tissue. EXAMPLES: Transverse fracture; comminuted fracture.

Transverse fracture

WHAT: A break running across the bone, roughly perpendicular to its long axis. EXAMPLES: A transverse fracture of the femur; a transverse fracture of the tibia.

Comminuted fracture

WHAT: A fracture in which the bone breaks into three or more pieces. EXAMPLES: Comminuted femur fracture; comminuted humerus fracture.

Greenstick fracture

WHAT: An incomplete fracture where the bone bends and cracks, common in children. EXAMPLES: Radius fracture; ulna fracture.

What are the 4 stages of bone fracture repair in order?

1. Hematoma formation → 2. Fibrocartilaginous (soft) callus formation → 3. Bony (hard) callus formation → 4. Bone remodeling.

Stage 1: Hematoma formation

Blood vessels break, blood collects at the fracture site, and a clot forms. Inflammation begins.

Stage 2: Fibrocartilaginous callus

A soft callus made of connective tissue and cartilage forms to help stabilize the broken bone.

Stage 3: Bony callus

Osteoblasts build new bone, replacing the soft callus with a hard bony callus.

Stage 4: Bone remodeling

Osteoclasts remove excess bone while osteoblasts build and reshape bone, restoring its strength and shape over time.

What is the difference between a soft callus and a bony callus?

A soft callus is made mainly of connective tissue and cartilage. A bony callus is made of new bone tissue.

What do osteoblasts and osteoclasts do during fracture repair?

Osteoblasts build bone; osteoclasts break down and remove bone so it can be reshaped.

what happens to the bone when it breaks then repairs?(quiz question)

When a bone breaks, blood vessels are damaged and a hematoma, or blood clot, forms at the fracture site. First, the hematoma forms and inflammation begins. Second, a soft fibrocartilaginous callus forms to connect and stabilize the broken ends. Third, osteoblasts form new bone, creating a hard bony callus. Finally, bone remodeling occurs as osteoclasts remove excess bone and osteoblasts build new bone, helping the bone regain its shape and strength.