Place the events of a fracture repair in order. A. A hematoma will form and will form a temporary connection between the ends of the bones.
B. Fibroblasts and chondroblasts migrate from the periosteum and begin to produce fibrocartilage to connect the ends of the bones.
C. Osteoclasts resorb dead portions of the new bony area, and compact bone replaces spongy bone.
D. Osteoprogenitor cells differentiate into osteoblasts and produce spongy bone.
E. Phagocytes and osteoclasts begin to remove dead and damaged tissue.
A) A, B,E, C,D. B) A, E,B, D,C. C) E, A,B, D,C. D) A, E,D, B,C.

The correct answer is: C) E,A,B,D,C.

Explanation:

Bone fractures occur when a trauma generated a breach in the continuity of the bone. When a bone fractures, a process called secondary healing starts.

The first step in fracture repair is the removal of dead tissues - this is done by specialized cells called phagocytes and osteoclasts, that proceed by "eating" the damaged tissues.

Next, a hematoma forms because the blood vessels surrounding the fractured bone were ruptured. This hematoma clots and forms the temporary frame for the process of healing that is happening.

Mesenchymal stem cells migrate to the area and begin to differentiate into fibroblasts and chondroblasts, which is important for the production of fibrocartilage, a tissue that will connect the ends of the broken bone.

Then, osteoprogenitor cells differentiate into osteoblasts, which are the cells that synthesize bone tissue. These osteoblasts will produce spongy bone. The newly-formed fibrocartilage tissue becomes calcified.

Finally, osteoclasts begin with a process called resorption, which consists of resorbing the dead portions of the new bony area. This resorption is coupled with osteoblasts' bone synthesis. These two processes that occur together are fundamental for bone remodeling, which will end up with the spongy bone being transformed into compact bone.

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