Endochondral ossification will form the center of primary ossification, and the cartilage extends by proliferation of chondrocytes and deposition of cartilage matrix. After this formation, chondrocytes in the central region of the cartilage start to proceed with maturation into hypertrophic chondrocytes.
After the primary ossification center is formed, the marrow cavity begins to expand toward the epiphysis. Then the subsequent stages of endochondral ossification will take place in several zones of the bone. Osteogenesis and Bone Regeneration. Bone has vascular tissue and cellular activity products, especially during growth which is very dependent on the blood supply as basic source and hormones that greatly regulate this growth process.
Bone-forming cells, osteoblasts, osteoclast play an important role in determining bone growth, thickness of the cortical layer and structural arrangement of the lamellae. Bone continues to change its internal structure to reach the functional needs and these changes occur through the activity of osteoclasts and osteoblasts.
The bone seen from its development can be divided into two processes: first is the intramembranous ossification in which bones form directly in the form of primitive mesenchymal connective tissue, such as the mandible, maxilla and skull bones. Second is the endochondral ossification in which bone tissue replaces a preexisting hyaline cartilage, for example during skull base formation.
The same formative cells form two types of bone formation and the final structure is not much different. Bone growth depends on genetic and environmental factors, including hormonal effects, diet and mechanical factors. The growth rate is not always the same in all parts, for example, faster in the proximal end than the distal humerus because the internal pattern of the spongiosum depends on the direction of bone pressure.
The direction of bone formation in the epiphysis plane is determined by the direction and distribution of the pressure line. Increased thickness or width of the bone is caused by deposition of new bone in the form of circumferential lamellae under the periosteum. If bone growth continues, the lamella will be embedded behind the new bone surface and be replaced by the haversian canal system.
Bone is a tissue in which the extracellular matrix has been hardened to accommodate a supporting function. The fundamental components of bone, like all connective tissues, are cells and matrix. Although bone cells compose a small amount of the bone volume, they are crucial to the function of bones. Four types of cells are found within bone tissue: osteoblasts, osteocytes, osteogenic cells, and osteoclasts.
They each unique functions and are derived from two different cell lines Figure 1 and Table 1 [ 1 , 2 , 3 , 4 , 5 , 6 , 7 ]. Osteoblast synthesizes the bone matrix and are responsible for its mineralization.
They are derived from osteoprogenitor cells, a mesenchymal stem cell line. Osteocytes are inactive osteoblasts that have become trapped within the bone they have formed. Osteoclasts break down bone matrix through phagocytosis. Development of bone precursor cells. Bone precursor cells are divided into developmental stages, which are 1. Bone cells, their function, and locations [ 1 , 2 , 3 , 4 , 5 , 6 , 7 ]. The balance between osteoblast and osteoclast activity governs bone turnover and ensures that bone is neither overproduced nor overdegraded.
These cells build up and break down bone matrix, which is composed of: Osteoid, which is the unmineralized matrix composed of type I collagen and gylcosaminoglycans GAGs. Calcium hydroxyapatite, a calcium salt crystal that give bone its strength and rigidity. Bone is divided into two types that are different structurally and functionally.
Most bones of the body consist of both types of bone tissue Figure 2 [ 1 , 2 , 8 , 9 ]: Compact bone, or cortical bone, mainly serves a mechanical function.
This is the area of bone to which ligaments and tendons attach. It is thick and dense. Trabecular bone, also known as cancellous bone or spongy bone, mainly serves a metabolic function. This type of bone is located between layers of compact bone and is thin porous. Location within the trabeculae is the bone marrow. Structure of a long bone. Long bones are composed of both cortical and cancellous bone tissue.
They consist of several areas Figure 3 [ 3 , 4 ]: The epiphysis is located at the end of the long bone and is the parts of the bone that participate in joint surfaces. The diaphysis is the shaft of the bone and has walls of cortical bone and an underlying network of trabecular bone.
The epiphyseal growth plate lies at the interface between the shaft and the epiphysis and is the region in which cartilage proliferates to cause the elongation of the bone. The metaphysis is the area in which the shaft of the bone joins the epiphyseal growth plate. Bone macrostructure. Different areas of the bone are covered by different tissue [ 4 ]: The epiphysis is lined by a layer of articular cartilage, a specialized form of hyaline cartilage, which serves as protection against friction in the joints.
The outside of the diaphysis is lined by periosteum, a fibrous external layer onto which muscles, ligaments, and tendons attach. The inside of the diaphysis, at the border between the cortical and cancellous bone and lining the trabeculae, is lined by endosteum. Compact bone is organized as parallel columns, known as Haversian systems, which run lengthwise down the axis of long bones. These columns are composed of lamellae, concentric rings of bone, surrounding a central channel, or Haversian canal, that contains the nerves, blood vessels, and lymphatic system of the bone.
The lamellae of the Haversian systems are created by osteoblasts. As these cells secrete matrix, they become trapped in spaces called lacunae and become known as osteocytes.
Osteocytes communicate with the Haversian canal through cytoplasmic extensions that run through canaliculi, small interconnecting canals Figure 4 [ 1 , 2 , 8 , 9 ]:. Bone microstructure. Compact and spongy bone structures. The layers of a long bone, beginning at the external surface, are therefore: Periosteal surface of compact bone. Bone development begins with the replacement of collagenous mesenchymal tissue by bone.
This results in the formation of woven bone, a primitive form of bone with randomly organized collagen fibers that is further remodeled into mature lamellar bone, which possesses regular parallel rings of collagen. Lamellar bone is then constantly remodeled by osteoclasts and osteoblasts. During intramembranous bone formation, the connective tissue membrane of undifferentiated mesenchymal cells changes into bone and matrix bone cells [ 10 ].
In the craniofacial cartilage bones, intramembranous ossification originates from nerve crest cells. The earliest evidence of intramembranous bone formation of the skull occurs in the mandible during the sixth prenatal week.
In the eighth week, reinforcement center appears in the calvarial and facial areas in areas where there is a mild stress strength [ 11 ]. Intramembranous bone formation is found in the growth of the skull and is also found in the sphenoid and mandible even though it consists of endochondral elements, where the endochondral and intramembranous growth process occurs in the same bone. The basis for either bone formation or bone resorption is the same, regardless of the type of membrane involved.
Periosteal bone always originates from intramembranous, but endosteal bone can originate from intramembranous as well as endochondral ossification, depending on the location and the way it is formed [ 3 , 12 ]. The statement below is the stage of intramembrane bone formation Figure 5 [ 3 , 4 , 11 , 12 ]: An ossification center appears in the fibrous connective tissue membrane.
Mesenchymal cells in the embryonic skeleton gather together and begin to differentiate into specialized cells. Some of these cells differentiate into capillaries, while others will become osteogenic cells and osteoblasts, then forming an ossification center. Bone matrix osteoid is secreted within the fibrous membrane. Osteoblasts produce osteoid tissue, by means of differentiating osteoblasts from the ectomesenchyme condensation center and producing bone fibrous matrix osteoid.
Then osteoid is mineralized within a few days and trapped osteoblast become osteocytes. Woven bone and periosteum form. The encapsulation of cells and blood vessels occur. When osteoid deposition by osteoblasts continues, the encased cells develop into osteocytes.
Accumulating osteoid is laid down between embryonic blood vessels, which form a random network instead of lamellae of trabecular. Vascularized mesenchyme condenses on external face of the woven bone and becomes the periosteum. Later, usually after birth, secondary ossification centers form in the epiphyses.
Ossification in the epiphyses is similar to that in the diaphysis except that the spongy bone is retained instead of being broken down to form a medullary cavity. When secondary ossification is complete, the hyaline cartilage is totally replaced by bone except in two areas. A region of hyaline cartilage remains over the surface of the epiphysis as the articular cartilage and another area of cartilage remains between the epiphysis and diaphysis.
This is the epiphyseal plate or growth region. Bones grow in length at the epiphyseal plate by a process that is similar to endochondral ossification. The cartilage in the region of the epiphyseal plate next to the epiphysis continues to grow by mitosis.
The chondrocytes, in the region next to the diaphysis, age and degenerate. Osteoblasts move in and ossify the matrix to form bone. This process continues throughout childhood and the adolescent years until the cartilage growth slows and finally stops. Wonder Words tiny fuse nose ear bone cell mature flexible collagen marrow enzyme fracture significant accumulate cortical cartilage calcium specialized Take the Wonder Word Challenge.
Join the Discussion. S Jan 22, I love watching these type of videos. But my one concern is, why whenever there is a title about that specific this but it never shows the actual video? Jan 22, Hi, Shania! Dante May 24, This was really cool in my opinion i did not know that bones grow months. May 24, We're so glad that you liked learning about this Wonder, Dante! Mar 14, Cool, Skyler!
Are you learning about bones at school, too? Jan 24, K Dec 2, I learned that bones grow int he video i hope wonderopolis stays real forever because if I had a kid im sure they would like wonderopolis.
Dec 2, Nov 4, Thanks, Kaylin! We hope that this Wonder helped you learn more about how bones grow! Jan 25, Ashley Apr 11, This is how you grow to be so tall! Apr 24, Jan 21, Jan 14, I just hurt my toe I think it's broke will it grow back?
Jan 19, Lauren Jan 13, I love growing because it helps me go on the rides I'm "56" inches. It's always fun when you can start to ride more rides, Lauren! Good point! Richtofen Jan 13, Jan 13, JK Jan 14, Hi, JK! Thanks for joining the conversation! We're not sure, but it does sound cool! Thanks for sharing what you learned, lydia! Kieran Jan 11, Wow, I didn't know that we grow because our bones fuse together. Jan 11, That's right, Kieran! You are actually born with more bones than you have as an adult!
Stewart Jan 8, I learned that the process in which the bones grow is called ossification. Bones stop growing the mid 20's. I also learned that your bones fuse together to make instead of from when you were born.
Jan 10, Mariah butler Jan 8, Babies actually do get alot of bones when they are born with Wow Jan 8, That's right, Mariah! We couldn't believe it either! In fact, a baby grows about 10" in the first year of life and grows several inches each year after that, especially during puberty. All of this growth is due to growing bones. Babies are born with about bones, and full-grown adults have only Babies have tiny bones compared with adults, of course.
As they grow, many of these bones fuse together to create larger bones. Their bones continue to grow until they reach their mids , when bones are as large as they will ever be.
Bones go through a number of changes as they grow. When babies are born, their bones are mostly cartilage, which is a soft and flexible substance. As babies grow, the cartilage in their bones grows. Over time and with a little help from calcium, bone replaces cartilage in a process known as ossification. Simply put, ossification is a process in which bone replaces cartilage. During ossification, layers of calcium and phosphate salts accumulate on and encase the cartilage cells. In time, the encased cartilage cells die.
As they die, the cartilage cells leave behind tiny pockets in the bone. Blood vessels grow into these pockets and deposit specialized cells, known as osteoblasts, into the empty spaces.
Osteoblasts perform a number of functions that help bones grow. These cells help to collect calcium into the pockets, which helps encase even more cartilage cells.
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