When bone forms by intramembranous ossification, the ossification centers are within
Multiple Choice
A hyeline cartilage.
B compact bone.
C mesenchyme.
D elastic cartilage.
E spongy bone.
The correct answer and explanation is:
Correct Answer: C. Mesenchyme
Explanation:
Intramembranous ossification is one of the two primary processes through which bone is formed, the other being endochondral ossification. Intramembranous ossification is responsible for the formation of flat bones, especially in the skull, face, mandible, and clavicle.
In intramembranous ossification, bone develops directly from mesenchymal tissue, which is an embryonic connective tissue that contains multipotent stem cells capable of differentiating into osteoblasts (bone-forming cells).
Here is a step-by-step summary of the process:
- Ossification centers form within mesenchyme:
Clusters of mesenchymal cells aggregate in specific regions and differentiate into osteoblasts, forming an ossification center. These cells begin secreting osteoid, the unmineralized organic component of bone. - Osteoid secretion and calcification:
The osteoblasts secrete osteoid, which then becomes mineralized with calcium salts. As calcification progresses, osteoblasts become trapped in the matrix and turn into osteocytes. - Formation of trabeculae (spongy bone):
The mineralized bone matrix forms trabeculae, or tiny struts, which create a structure known as woven bone. Blood vessels grow into the area, and mesenchyme condenses around the bone to form the periosteum. - Formation of compact bone:
Over time, the superficial layers of woven bone are remodeled into compact bone, while the deeper regions may remain as spongy bone.
Why the Other Options Are Incorrect:
- A. Hyaline cartilage – This is involved in endochondral ossification, not intramembranous ossification.
- B. Compact bone – Compact bone forms later in the process; it is not the initial site.
- D. Elastic cartilage – This type of cartilage is found in structures like the ear; it’s not involved in ossification.
- E. Spongy bone – Spongy bone results from intramembranous ossification but is not where the process begins.
Conclusion: Intramembranous ossification begins in the mesenchyme, making C the correct answer.