Bone Formation and Ossification

Questions and Answers

What is the term given to the process of formation and development of bone connective tissue?

Ossification or osteogenesis

What is the type of ossification that produces the flat bones of the skull, some of the facial bones, the mandible, and the central part of the clavicle?

Intramembranous ossification

At what week of embryonic development does the skeleton begin forming?

Eighth through twelfth weeks

What type of cells are formed when some cells in the thickened, condensed mesenchyme divide and differentiate during intramembranous ossification?

Osteoprogenitor cells Signup and view all the answers

What is the term given to the thin layer of mesenchyme in areas where intramembranous ossification occurs?

Membrane Signup and view all the answers

What is the type of connective tissue that has mesenchymal cells and abundant ground substance, and is the source of bones formed through intramembranous ossification?

Mesenchyme Signup and view all the answers

What is the first step in intramembranous ossification?

Ossification centers form within thickened regions of mesenchyme Signup and view all the answers

What is the function of osteoblasts in intramembranous ossification?

To secrete osteoid Signup and view all the answers

What is the term for the growth of capillaries and osteoblasts that extends from the periosteum into the core of the cartilage shaft?

Periosteal bud Signup and view all the answers

What is the primary function of the primary ossification center?

To initiate bone formation in the diaphysis Signup and view all the answers

What is the process by which osteoclasts resorb some bone matrix within the diaphysis?

Creating a hollow medullary cavity Signup and view all the answers

What is the term for the cartilage that remains on the articular surface of each epiphysis?

Articular cartilage Signup and view all the answers

At what age do most epiphyseal plates typically ossify and lengthwise bone growth is complete?

Between 10 and 25 years Signup and view all the answers

What is the purpose of the epiphyseal plate during bone growth?

To allow for lengthwise bone growth Signup and view all the answers

What is the term for the process by which bone replaces hyaline cartilage in the epiphyses?

Secondary ossification Signup and view all the answers

What is the function of osteoblasts in endochondral ossification?

To produce osteoid Signup and view all the answers

What is the term for the remains of the calcified cartilage that serve as a template for osteoid production?

Template Signup and view all the answers

What is the end result of endochondral ossification in terms of bone growth?

Formation of a fully formed bone Signup and view all the answers

What is the outcome when calcification entraps osteoblasts within lacunae in the matrix?

The entrapped cells become osteocytes. Signup and view all the answers

What type of bone is initially formed during intramembranous ossification?

Woven bone (or primary bone) Signup and view all the answers

What is the term for the process where lamellar bone replaces woven bone?

Remodeling Signup and view all the answers

What is the typical structure of a flat cranial bone?

Two external layers of compact bone with a layer of spongy bone in between Signup and view all the answers

When does intramembranous ossification begin?

In the mesenchyme, which is gradually transformed into bone Signup and view all the answers

What type of ossification produces most bones of the skeleton, including those of the upper and lower limbs, the pelvis, the vertebrae, and the ends of the clavicle?

Endochondral ossification Signup and view all the answers

During endochondral ossification, what happens to the chondrocytes in the cartilage model?

They hypertrophy, resorb cartilage matrix, die, and disintegrate Signup and view all the answers

What is formed when the perichondrium surrounds the cartilage model?

A periosteal bone collar Signup and view all the answers

What is the primary ossification center formed in?

The diaphysis Signup and view all the answers

What happens to the cartilage matrix as chondrocytes enlarge?

It calcifies Signup and view all the answers

Study Notes

Bone Formation

Ossification, or osteogenesis, refers to the formation and development of bone connective tissue.
It begins in the embryo and continues as the skeleton grows during childhood and adolescence.

Intramembranous Ossification

Also known as dermal ossification, it produces flat bones of the skull, some facial bones, mandible, and the central part of the clavicle.
It begins when mesenchyme thickens and condenses with a dense supply of blood capillaries.
The process involves four main steps:
- Ossification centers form within thickened regions of mesenchyme.
- Osteoprogenitor cells differentiate into osteoblasts, which secrete osteoid.
- Osteoid undergoes calcification, entrapping osteoblasts within lacunae.
- Woven bone and its surrounding periosteum form, which is eventually replaced by lamellar bone.
The resulting bone tissue is initially immature and not well organized (woven bone), but eventually becomes compact bone and spongy bone.

Endochondral Ossification

Begins with a hyaline cartilage model and produces most bones of the skeleton, including those of the upper and lower limbs, pelvis, vertebrae, and ends of the clavicle.
The process involves six steps:
- Fetal hyaline cartilage model develops.
- Cartilage calcifies, and a periosteal bone collar forms.
- Chondrocytes hypertrophy and resorb surrounding cartilage matrix, producing larger holes.
- Chondrocytes die and disintegrate, and blood vessels grow toward the cartilage.
- Osteoblasts develop and secrete osteoid around the calcified cartilage shaft.
- Primary ossification center forms in the diaphysis, and bone development extends toward the epiphyses.
Secondary ossification centers form in the epiphyses, and bone replaces almost all cartilage, except articular cartilage and epiphyseal cartilage.
Lengthwise bone growth continues until the epiphyseal plates ossify and form epiphyseal lines, indicating that the bone has reached its adult length.

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Description

Learn about the process of bone formation and development, including intramembranous ossification and osteogenesis. Understand how the skeleton grows during childhood and adolescence.