(1) Growth Plate Chondrocytes: Skeletal Development, Growth and Beyond

Endochondral Ossification

The development process in which the initial cartilage template is systematically replaced by bones

Mesenchymal Cells

A type of adult stem cells in bone marrow, adipose tissue, and the umbilical cord

Chondrocytes

A cell that forms the scaffold and instructs the osteoclasts to form the bone matrix

Derived from undifferentiated mesenchymal cells

What is another use for chondrocytes past initial bone creation?

Bone remodeling and regeneration during fracture healing

Hypertrophic

Abnormally enlarged

Denotes the final, specialized stage of the cell

(Primary/Secondary) Ossification Center

The original point of bone creation

Vascularized

Creation and interaction of blood vessels

Stimulated primarily by vascular endothelial growth factor (VEGF)

Indian Hedgehog Protein (Ihh)

A cell-signaling molecule important to bone development and stem cell maintenance

Apoptosis

Programmed, controlled cell death to maintain tissue balance and health

OR, transdifferentiate into osteoblasts

Epiphysis

The enlarged wide end of a long bone that articulates with other bones at joints.

Secondary ossification center here

Articular Cartilage

The smooth, tough tissue that lines the ends of bones in a joint, cushioning the bones from frictional movement

SRY-Box 9 (Sox9)

A master transcription factor expressed by mesenchymal cells that clumps cells together and then kills some off (apoptosis) to refine shape of tissue

Necessary for differentiation into chondrocytes

Resting Zone

The first zone characterized by chondrocytes with minimal cell division

Spatially determines the other zones like proliferating and hypertrophic zones

Reservoir for quiescent skeletal stem cells

Quiescent Skeletal Stem Cells

A cell cycle arrest with no cell division but maintenance with metabolically active niche to preserve stem cell potential

PTHrP

Parathyroid related protein

Stimulates proliferation

Proliferation

Cell division

POC

Primary ossification center

SOC

Secondary ossification center

Ihh

indian hedgehog protein

Osteoblasts

bone builder cells

Osteoclasts

bone demolisher cells

Primary Spongiosa

The initial stage of the newly formed, mineralized spongy bone.

Col10a1-cre

Postnatal Hypertrophic Chondrocytes (Type X Collagen as a marker)

Trabecular Bone (Cancellous Bone)

A porous, spongy type of bone tissue found in the epiphyses

Cortical Bone

Dense, compact bone tissue that forms the outer layer of long bones

Stromal Cells

A diverse class of supportive, connective tissue cells that form the structural framework of organs and provide functions like nourishment, waste removal, and immune regulation.

Progenitor Cells

Partially differentiated, unspecialized cells that could divide and differentiate more, but are more restricted than true stem cells.

Periarticular Chondrocytes

Round, slowly dividing cartilage cells near the ends of the developing bone, close to where the joints will form

(AKA, pre-step of columnar chondrocytes)

Columnar Chondrocytes

Flattened, rapidly proliferating cells organized into vertical columns.

(AKA, evolved form of periarticular chondrocytes)