Bone formation begins when secrete the initial semisolid organic form of bone matrix called .

a. osteoblasts

b. osteoid

Explanation:

Osteoblasts are the fundamental cell of bone tissue. They are the cells that synthesize the bone matrix called osteoid from which it is made from the skeleton of bone fish, to the skeleton of humans. Since the bone skeleton is an evolutionary paraphiletic characteristic (it is present in several taxonomic groups that have evolved from the same ancestor).

Osteoblasts are responsible for the development and growth of bones during the juvenile stage of individuals and are also responsible for maintaining adult bone and regenerating bone when it breaks.

Osteogenesis is the process of differentiation of osteoblasts. The cells from which osteoblasts differ are called osteoprogenitors. The differentiation of osteoprogenitor cells, which come from the mesoderm, periosteum or bone marrow, is induced by growth factors called bone morphogenetic proteins (BMPs), capable of inducing the growth of bone, cartilage or connective tissue. When an osteoprogenitor cell receives a BMP signal, it quickly begins to express the genes to generate collagen, osteonectin and alkaline phosphatase, among other compounds necessary for bone growth. When the bone grows, it ends up wrapping some of the osteoblasts and they lose their ability to replicate, at that time they are dedicated to bone maintenance and not to their synthesis and are called osteocytes.