Osteocytes's Role In Bone Homeostasis

One of the key elements of regulating skeletal growth is the Osteoclasts. The Osteoclasts are responsible for initiating the bone remodeling cycle. Blood vessels and nerves are able to penetrate the bone once the chondrocytes die

Longitudinal bone growth occurs at the epiphyseal plate, which is a thin layer of cartilage between the epiphyseal and metaphyseal bone at the distal ends of the long bones. Bone growth is the result of maturation, growth of chondrocytes, their production of bone matrix, and finally calcification (47). The growth plate is a complex structure consisting of different layers of cells, as shown in figure 3. The most immature cells, the stem cells, are found towards the epiphyseal end of the growth plate in the stem cell zone, or resting zone; the proliferating zone contains more mature chondrocytes and the hypertrophic zone contains the larger chondrocytes. The resting stem cells in the resting zone are recruited, whereupon proliferation and differentiation

Bone is a living tissue and made up of cartilage. Fibrodysplasia ossificans progressiva bone appears as normal bone tissue, but it develops in the wrong places. Osteogenesis and ossification are medical terms which refer to the formation of bone. Most bones in the human body grow and heal up after a break through endochondral bone formation, which is how FOP bones grow. Cartilage forms first and then the bone will eventually take the place of cartilage.

Bone is surrounded by a thin membranous layer of soft tissue called periosteum (Singh, 2017). When the bone breaks it bleeds from torn ends because of the disruption of the supplying blood vessels. And quite naturally the periosteum is also torn. A fracture hematoma forms and white blood cells march in to clean up the area that is injured. The periosteum is the primary source of osteoblasts, which plays a huge role in fracture healing (Singh, 2017). After the hematoma formation, the next step is callous formation with the formation of cartilage and bone and then the remodeling phase consisting of the osteoclasts and the osteoblasts reshaping the bone to its original state (Patton, 2012).

What are the roles of osteoclasts in bone formation? Osteoclasts are large cells that function to reabsorb, or to digest bone tissue. They digest bone tissue from the inner sides of bones thus enlarging the inner bone cavity so that the bone does not become overly thick and heavy.

Osteoporosis is an age-related disease of the skeletal system characterized by both low bone mass and bone structural degeneration (Nunes, 2011). Understanding osteoporosis is important because it is continues to be overlooked and undertreated, causing high numbers of bone fractures each year –in the elderly, these bone fractures can be debilitating or even life threatening (Eastell, 2009). Osteoporosis manifests when an imbalance between bone resorption and bone rebuilding occurs – this is due to changes in osteoclast and osteoblast activity. I chose this topic because osteoporosis affects millions of people, and research will allow me to better understand this common yet complex, and very perilous bone disease.

Bone is a living organism that is continuously regenerating its self through two stages (formation and resorption). In the resorption stage old bone is broken down then removed by cells. Then in the formation stage, new bone is built to replace the old by cells called osteoclasts. When the human body is younger more bone is produced than removed and as the body grows in age it’s the opposite also known as primary osteoporosis since it isn’t caused by other condition or long time medication.

The structural unit in compact bone is called the Haversian system and is organized as parallel columns, which run lengthwise down the axis of long bones. The Haversian system consists of the Haversian canal (central canal), a layer of lamellae (bone matrix), tiny spaces (lacunae) between the lamellae, osteocytes (bone cells) within the lacunae and canaliculi (small channels). Trabeculae are plates in spongy bone that branch and connect with one and another. The process of forming a new HAVERSIAN system and new Trabeculae begin with a process called remodeling, this is a process in which an existing bone is reabsorbed a new bone is laid down to replace it there several phases that occur to reach this. Phase one is Activation:

The Osteoblast is one of the four bone cells found inside the human body. They create bones. An Osteoblast creates the new layer of bone. The another type is called an Osteocyte. An Osteocyte can be formed from an Osteoblast while new bone is in process of creation. They get surrounded after formation. They don’t get completely barricaded because of they send out very long windy branches which connect to other Osteocytes. They can sense cracks and pressures to help direct or send Osteoclasts to dissolve the bone. Osteoclasts are large cells that dissolve the bone. They are formed when two bone cells fuse together. They come from the bone marrow. They usually have more than one nucleus when they form together. They are found on the surface

As the remodeling process that conducts by both of the cells is unstable, the bone tissues are affected too. Bones consists of two types of bones tissue which is compact bone and spongy bone. Compact bone also known as cortical bone is the hard outer layer of the bone and it is found beneath the periosteum. It provides support and protection and withstands the stress produce by weight and movement. Meanwhile, spongy bone also called as trabecular or cancellous bone is usually found at the end of the long bones. The spongy bone tissues have a honey-comb like structure. In osteoporosis, the bones tissue start to break down faster than it can regenerate. Hence, the bones tissue slowly lose their density and becomes thinner. Plus,the holes structure

4.Osteoclasts are the other cell that are present during bone remodeling. Osteoclasts are responsible for eating away at excess bone matrix formed by the

The bones develop and grow in different ways. One way the bones develop is endochondral ossification. Endochondral ossification involves the replacement of cartilage with bone tissue. Another way bones develop is Intramembranous ossification. Intramembranous ossification consists of the replacement of sheet like tissue membranes with bony tissue. The bones grow in length at the epiphyseal plate by a process similar to endochondral ossification. The cartilage next to the epiphysis grows by mitosis. The chondrocyte age and degenerate. Osteoblasts move in form bone. Bones stop growing in early

Research into Osteoimmunology, a term first coined nearly 60 years ago, has markedly picked up steam in the past decade, as we have unravelled more of the involvement(4) of the immune cells in the regulation of bone repair.

As a results of osteoclast death, the remodeling site becomes free of osteoclasts (Del Fattore , Teti ,and Rucci 2008). Phase 3: osteoblast precursors proliferate and differentiate at the remodeling site and start synthesizing new collagen matrix (Wilson 2011). They also initiate matrix mineralization by releasing small matrix vehicles which include Ca and phosphate and ALP (Anderson 2003). Additionally, the osteoblasts produce different factors that are stored within the newly synthesized bone for future use and released during subsequent remodelling cycles (Kang 2012). Phase 4: As bone formation persists, osteoblasts be come entrenched more deeply into the bone and eventually become surrounded by bone and are

4. Pre-osteoblasts are recruited by cytokines: transforming growth factor beta, insulin growth-like factors, fibroblast growth factors and bone morphogenetic proteins (BMPs) (Hock et al, 2004). The actions of BMPs cause pre-osteoblasts to differentiate into osteoblasts (Monolagas, 2000). Osteoblasts then secrete bone matrix proteins: type-I collagen, osteocalcin, proteoglycans, growth factors and glycoproteins into the resorption pits (Nair et al, 1996). Approximately 50% of osteoblasts then undergo apoptosis and the remaining become embedded osteocytes or bone lining cells.