Info

Developing periosteum

Cartilaginous Calcified model cartilage

-Primary ossification center

Blood vessel

Secondary ossification center

Remnants of epiphyseal Articular plate \ cartilage r

Secondary ossification center r

Secondary ossification center

Compact bone

-Epiphyseal plate

Medullary cavity

Secondary ossification center

Compact bone

Medullary cavity

Medullary cavity

Epiphyseal plate

Medullary cavity

Epiphyseal plate

Remnant of epiphyseal plate

Remnants of epiphyseal Articular plate \ cartilage

Spongy bone

Medullary cavity

Spongy bone

Spongy bone

Medullary cavity

Spongy bone

Articular cartilage

Figure

Major stages (a-f) in the development and growth of an endochondral bone. (Relative bone sizes not to scale.)

Endochondral Bones

Most of the bones of the skeleton are endochondral bones (en'do-kon'dral bonz). They develop from masses of hyaline cartilage shaped like future bony structures. These cartilaginous models grow rapidly for a time and then begin to change extensively. For example, cartilage cells enlarge and their lacunae grow. The surrounding matrix breaks down, and soon the cartilage cells die and degenerate.

About the same time, a periosteum forms from connective tissue that encircles the developing structure. As the cartilage decomposes, blood vessels and undifferenti-ated connective tissue cells invade the disintegrating tis sue. Some of the invading cells differentiate into osteoblasts and begin to form spongy bone in the spaces previously housing the cartilage. Once completely surrounded by the bony matrix, osteoblasts are called osteocytes. As ossification continues, osteoblasts beneath the periosteum deposit compact bone around the spongy bone.

The process of forming an endochondral bone by the replacement of hyaline cartilage is called endochondral ossification. Its major steps are listed in table 7.1 and illustrated in figure 7.8.

In a long bone, bony tissue begins to replace hyaline cartilage in the center of the diaphysis. This region is called the primary ossification center, and bone develops

2. Cells undergoing mitosis

3. Older cells enlarging and becoming calcified

4. Dead cells and calcified intercellular substance

Bone tissue of epiphysis

1. Resting cells

Bone tissue of epiphysis

1. Resting cells

2. Cells undergoing mitosis

3. Older cells enlarging and becoming calcified

4. Dead cells and calcified intercellular substance

Osteoblast depositing osseous tissue

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

Get My Free Ebook


Post a comment