Bone Growth and Bone Remodeling

Flashcards covering long bone interstitial and appositional growth, including the five zones of the epiphyseal plate and periosteal remodeling.

What is interstitial growth in long bones?

Interstitial growth is growth in bone length that depends on the growth of cartilage within the epiphyseal plate.

What is appositional growth in long bones?

Appositional growth is growth in bone diameter or thickness that occurs within the periosteum.

What characterizes Zone 1 (Zone of resting cartilage) in the epiphyseal plate?

It is nearest the epiphysis, composed of small chondrocytes in cartilage matrix resembling hyaline cartilage, and secures the epiphysis to the epiphyseal plate.

What occurs to chondrocytes in Zone 2 (Zone of proliferating cartilage)?

Chondrocytes undergo rapid mitotic cell division, enlarge slightly, and align into longitudinal columns within their lacunae that look like stacks of coins.

What changes take place in Zone 3 (Zone of hypertrophic cartilage)?

Chondrocytes cease dividing and greatly enlarge in size (hypertrophy), and lacunae walls thin as chondrocytes resorb matrix.

What causes chondrocyte destruction and matrix opacity in Zone 4 (Zone of calcified cartilage)?

Minerals are deposited in the matrix between lacuna columns, limiting nutrient diffusion and causing chondrocyte destruction.

What occurs during bone matrix deposition in Zone 5 (Zone of ossification)?

Lacuna walls break down to form longitudinal channels invaded by capillaries and osteoprogenitor cells, which develop into osteoblasts that deposit new bone matrix.

Which specific zones of the epiphyseal plate are directly responsible for growth in bone length?

Zone 2 (where chondrocytes undergo mitotic cell division) and Zone 3 (where chondrocytes hypertrophy).

How does a child's epiphyseal plate appear on an x-ray?

It appears as a dark line between the epiphysis and the diaphysis of a long bone.

What structure replaces the epiphyseal plate once bone interstitial growth ceases at maturity?

An internal thin line of compact bone called an epiphyseal line.

How do osteoblasts contribute to appositional growth within the periosteum?

Osteoblasts in the inner cellular layer of the periosteum produce and deposit bone matrix in layers parallel to the surface called external circumferential lamellae.

What is the role of osteoclasts during appositional growth?

Osteoclasts resorb bone matrix along the inner medullary cavity, expanding the medullary cavity as new bone is added to the periphery.