What Are Osteoprogenitor Cells?

Bone progenitor cells are preosteoblasts. Because the periosteum, cortical bone, inside and outside the periosteum, and bone surface are covered with a layer of osteoprogenitor cells, its thickness varies with age and the surface of the bone. The morphology of bone progenitor cells is similar to that of intracellular or fibroblasts. The cells are slender, with light nuclei and cytoplasm. Bone progenitor cells are also a type of bone tissue cells. They belong to primitive mesenchymal cells and have multipotential potential. Due to different nature and degree of physiological signal stimulation, osteoprogenitor cells can differentiate into osteocytes, and osteogenitor cells are located in the outer and endosteal bone formation of connective tissue close to the bone tissue. The cells are smaller, spindle-shaped, elliptical, and have less cytoplasm. Osteoblasts are stem cells of bone tissue, which become osteoblasts with bone growth, reconstruction, and differentiation. Bone cells and fibroblasts.

Chinese name: Bone progenitor cells
Foreign name: osteoprogenitor cell

Nature: cell
Shape: Slender

Physiological significance of bone progenitor cells

It has the potential for division and differentiation, is spindle-shaped, and has small finger-like protrusions. Nuclei oval, lightly colored. The cytoplasm is weakly basophilic or eosinophilic, contains glycogen, has few mitochondria, and the Golgi complex and endoplasmic reticulum are underdeveloped. When differentiated into osteoblasts, the rough endoplasmic reticulum increases and glycogen decreases. Osteoblasts are found in the deepest layers of the endosteal and periosteum. In the process of osteogenesis, growth, reconstruction or repair, osteogenic cells divide and multiply, and become osteoblasts.

Classification and function of bone progenitor cells

The cytoplasm of bone cells contains only a small amount of mitochondria, Golgi complex, and rough endoplasmic reticulum, which indicates that this cell belongs to mature cells and no longer shows its functional activities. However, according to research in recent years, although bone cells have no obvious functional activities such as secretion and synthesis, under certain conditions, they can promote the dissolution of calcium in bone and release calcium into the blood, which can maintain blood calcium concentration or Regulation of blood calcium balance. At the same time, when the surrounding environment changes, it can still turn into another cell. For example, when the bone around the bone pit is absorbed, the osteocytes are free and can become osteoblasts, or several osteocytes combine to become multinucleated osteoclasts.

The cellular components of bone tissue include osteoblasts, osteoblasts, bone cells and osteoclasts. Only bone cells exist in the bone tissue, and the other three cells are located at the edges of the bone tissue.

Bone progenitor cells

Bone cells are flat oval-shaped multi-protrusion cells, and the nucleus is also oblate and stained deeply. The cytoplasm is weakly basophilic. Under the electron microscope, there were a small amount of lysosomes, mitochondria, and rough endoplasmic reticulum in the cytoplasm, and the Golgi complex was not well developed. Bone cells are sandwiched between two adjacent bone plates or are scattered in the bone plates. There are gap connections between the protrusions of adjacent bone cells. In the bone matrix, the oval-shaped cavity occupied by the bone cell body is called bone lacun, and the space where the protrusions are located is called bone canaliculi. Adjacent bone pits are connected to each other by bone tubules. Bone pits and tubules contain interstitial fluid from which bone cells obtain nutrients.

Osteogenic cells

Osteoblasts are stem cells in bone tissue. The cells are spindle-shaped, the cell body is small, the nucleus is oval, and the cytoplasm is weakly basophilic. Osteoblasts exist in the inner layer of the periosteum and endosclera and in the central tube, near the surface of the bone matrix. It can divide and proliferate and differentiate into osteoblasts during bone growth and development, or during bone remodeling or bone tissue repair in adulthood.

Osteoprogenitor cells

Osteoblasts are differentiated from osteoblasts, which are larger than osteoblasts, and are short columnar or cubic with small protrusions. The nucleus is large and round with clear nucleoli. The cytoplasm is basophilic and is rich in alkaline phosphatase. Under the electron microscope, there were a large number of rough endoplasmic reticulum, free ribosomes, and developed Golgi complexes, and there were more mitochondria in the cytoplasm. When bone grows and regenerates, osteoblasts are arranged in a regular layer on the surface of bone tissue, secrete matrix and fibers to the surroundings, and embed itself in them to form osteoid. It becomes bone tissue, and osteoblasts mature into bone cells.

Osteoblasts secrete membrane-coated vesicles into the osteoid in the manner of apical secretion, called matrix vesicles, with a diameter of about 0.1 m. There are a large number of alkaline phosphatase and ATPase on the vesicle membrane, and the vesicle contains phospholipids and small calcium salt crystals. Matrix vesicles are generally considered to be important structures for osteoid calcification. Scientific research suggests that osteoblasts can secrete osteocalcin into the matrix.

Osteoclast

Osteoclasts are large, multi-nucleated cells with a diameter of up to 100 m and 2 to 50 nuclei. They have strong eosinophilic cytoplasm. It is much smaller than osteoblasts. Mostly located in the pit formed by the bone tissue absorption site. Under the electron microscope, osteoclasts have many high and dense microvilli near the bone tissue, forming ruffled borders. The cytoplasm at the base contains a large number of lysosomes and swallowing vesicles. Calcium salt crystals and dissolved organic ingredients. There is a circular cytoplasmic area around the wrinkle margin, which contains only microfilaments and few other organelles, called the clear zone. The cell membrane in the bright area is flat and clings to the surface of the bone tissue, just like a fence around the fold edge, forming a microenvironment at the closed fold edge. Osteoclasts can release a variety of proteases, carbonic anhydrase, and lactic acid into it to dissolve bone tissue. Academia believes that osteoclasts are a fusion of multiple monocytes.