Detailed Study Notes on Bone Development and Skeletal Tissues

Ossification (Osteogenesis)

The process of bone tissue formation.

Bone Remodeling and Repair

An ongoing process throughout life for bone maintenance.

Endochondral Ossification

Bone formation by the replacement of hyaline cartilage, forming most of the skeleton except flat skull bones and clavicles.

Intramembranous Ossification

Bone development from fibrous membranes, primarily in flat bones (e.g., frontal, parietal, occipital, temporal bones, and clavicles).

Primary Ossification Center

Located in the center of the shaft during endochondral ossification, where blood vessel infiltration converts perichondrium to periosteum, leading to osteoblast formation.

Periosteal Bud Invasion

Invades existing cavities during endochondral ossification, leading to the formation of spongy bone alongside blood vessels and nerves.

Interstitial (Longitudinal) Growth

Bone growth responsible for increasing the length of long bones.

Appositional Growth

Bone growth responsible for increasing bone thickness (width).

Epiphyseal Plate (Cartilage)

Essential for interstitial growth, maintaining constant thickness by growing on one side while being replaced by bone on the other.

Resting Zone (Epiphyseal Plate)

Relatively inactive cartilage on the epiphyseal side of the epiphyseal plate.

Proliferation Zone (Epiphyseal Plate)

Rapidly dividing cartilage cells that push the epiphysis away from the diaphysis.

Hypertrophic Zone (Epiphyseal Plate)

Older chondrocytes enlarge and erode their lacunae.

Calcification Zone (Epiphyseal Plate)

Cartilage matrix undergoes calcification; chondrocytes die, and a vascular invasion occurs.

Ossification Zone (Epiphyseal Plate)

Spicules of calcified cartilage are eroded by osteoclasts and replaced with bone by osteoblasts.

Osteoblasts

Cells that secrete osteoid (unmineralized bone matrix) and are involved in bone deposition.

Osteoclasts

Cells that resorb/break down bone matrix by secreting lysosomal enzymes and protons (\text{H}^+).

Osteoid

An unmineralized band of bone matrix secreted by osteoblasts, marking new bone deposition.

Bone Remodeling

The continuous process of bone deposition and resorption occurring at the periosteum and endosteum surfaces.

Parathyroid Hormone (PTH)

A regulatory hormone that elevates blood calcium levels by stimulating osteoclast activity.

Calcitonin

A regulatory hormone that can temporarily lower blood calcium levels, especially in high doses.

Wolff's Law

The concept that bones adapt in response to mechanical stressors, increasing in thickness where necessary to withstand greater forces.

Diaphysis

The central shaft of a long bone.

Epiphysis

The ends of long bones.

Periosteum

A dense fibrous membrane covering the external surface of bone.

Endosteum

A delicate connective tissue membrane lining internal bone surfaces.

Calcium Homeostasis

The process of maintaining blood calcium levels within a narrow range (9-11 \text{ mg/dl}), critical for nerve impulse transmission, muscle contraction, blood coagulation, and cell division.