3.7 Bone Formation

These flashcards cover key terms and concepts related to the skeletal system, including bone cells, ossification processes, and the healing of fractures.

Osteogenic Cell

A stem cell that gives rise to most other bone cell types and is capable of undergoing mitosis.

Osteoblasts

Bone-forming cells that deposit the bone matrix but are not capable of mitosis.

Osteocytes

Mature bone cells that are trapped within the bone matrix and maintain bone tissue.

Osteoclasts

Bone-dissolving cells derived from white blood cells, responsible for resorption of bone.

Mesenchyme

An embryonic tissue type that loosely organizes connective and skeletal tissues.

Intramembranous Ossification

A type of bone formation that produces the flat bones of the skull and most of the clavicle. These bones are typically thin.

Endochondral Ossification

The process by which most bones of the body develop, including the vertebrae, ribs, scapula, pelvis, and bones of the limbs. It begins around the sixth week of fetal development and continues intoa persons 20s. Unlike 

Hematoma Formation

The initial process in fracture healing where blood clots form at the site of the fracture.

Soft Callus Formation

The stage in fracture healing where collagen and fibrocartilage are deposited to hold fractured elements together.

Hard Callus Formation

The stage in fracture healing where osteoblasts lay down bone matrix making the callus hard.

Bone Remodeling

The lifelong process in which osteoblasts and osteoclasts work together to adapt bone structure based on stress.

Epiphyseal Plate

The area of cartilage where bone can grow in length during childhood.

Calcification

The process by which bone matrix hardens as minerals are deposited.

Resorption

The process by which osteoclasts break down bone and return minerals to the bloodstream.

Trabeculae

The honeycomb structure found in spongy bone that allows for lightweight bone formation.

Hypertrophy

Cell enlargement that stimulates surrounding extracellular matrix to calcify during cartilage growth.

The five steps of Intramembranous Ossification and what happens in each:

Step 1.) Condesation of Mesenchyme (soft tissue clumps): Mesenchymal (embryonic connective tissue) condenses into a soft sheet-like structure where bone will form.

Step 2.) Formation of Ossification Centers: A center for bone formation appears in this soft tissue. Blood vessels grow into the area.

Step 3.) Calcification (harding begins): Osteogenic cells become osteoblasts. Osteoblasts start laying down bone material. As they get trapped they become osteocytes, living in lacunae and forming canaliculi. This material hardens, forming early bone.

Step 4.) Formation of Trabeculae (Spongy bone forms): Hardened pieces of trabecular (bone) create spongy bone (which looks like honeycomb). Blood vessels weave through this network.

Step 5.) Development of the Periosteum (Compact bone and covering): Osteoblast on the surface keep laying down material, creating a layer of compact (dense) bone. The periosteum (a tough outer covering) forms around the bone. It has osteogenic cells that make new osteoblasts for ongoing bone formation.