University of Texas Medical Branch

Cell Biology Graduate Program

Look at slide 20 and find region showing two adjacent long bones that are developing. Look for the primary ossification center in the diaphysis and move towards the epiphysis.  There you should see the epiphyseal plate which is an area of growth in long bones as well as endochondral bone development (from a cartilage matrix).  The above photo is not from slide 20, but you can see the cartilage to the left and the different regions in the epiphysial plate near the center of the slide.   Test yourself:  can you identify the zones in this photograph before you go further? 

This photo is from your slide 20 and shows the resting zone (RZ) of hyaline cartilage. Then there is the zone of proliferation and the zone of hypertrophy.  Identify these regions on your slide 20.  How is the zone of proliferation significant to the growth in length.     What does the zone of hypertrophy signify?

Higher magnifications of the resting zone and the zone of proliferation are shown in this photo.

This photo shows higher magnifications of which zones?

Why do the chondrocytes die?

What happens to the calcified cartilage?

In your slide 20 look at the diaphysis showing new bone and identify the spicules of bone forming over the model formed by  cartilage matrix.  The cartilage matrix is purple-blue and the newly laid bone is bright red. This can best be seen in the higher magnification shown below.   What cells are responsible for laying down bone?   What cells are responsible for removing bone so it can be remodeled?