Explain the differences between cortical and trabecular bone in terms of both th

Question

Explain the differences between cortical and trabecular bone in terms of both the microstructure and biomechanical properties of each type of bone. Why is there no trabecular bone present in the mid-shaft regions of long bones (e.g. the femur or tibia)? Why is trabecular bone present at the distal ends of long bones? Which type of bone is more adaptable to changes in mechanical stress? Explain your answer and give examples of how the more adaptable bone changes its structure in response to changes in mechanical stress fields.

Explanation / Answer

answer 1

Cortical bone is arranged for facilitating following functions

The trabeculae of spongy bone follow the lines of stress and can realign if the direction of stress changes.

Cancellous bone has a greater surface area and is ideal for metabolic activity e.g. exchange of calcium ions.

In osteoporosis, cancellous bone is more severely affected than cortical bone

answer 2 Primary center of ossification

The first site of ossification occurs in the primary center of ossification, which is in the middle of diaphysis (shaft). Then:

The perichondrium becomes the periosteum. The periosteum contains a layer of undifferentiated cells (osteoprogenitor cells) which later become osteoblasts.

The osteoblasts secrete osteoid against the shaft of the cartilage model (Appositional Growth). This serves as support for the new bone.

Chondrocytes in the primary center of ossification begin to grow (hypertrophy). They stop secreting collagen and other proteoglycans and begin secreting alkaline phosphatase, an enzyme essential for mineral deposition. Then calcification of the matrix occurs and osteoprogenitor cells that entered the cavity via the periosteal bud, use the calcified matrix as a scaffold and begin to secrete osteoid, which forms the bone trabecula. Osteoclasts, formed from macrophages, break down spongy bone to form the medullary (bone marrow) cavity.

Secondary center of ossification

About the time of birth in mammals, a secondary ossification center appears in each end (epiphysis) of long bones. Periosteal buds carry mesenchyme and blood vessels in and the process is similar to that occurring in a primary ossification center. The cartilage between the primary and secondary ossification centers is called the epiphyseal plate, and it continues to form new cartilage, which is replaced by bone, a process that results in an increase in length of the bone. Growth continues until the individual is about 20 years old or until the cartilage in the plate is replaced by bone. The point of union of the primary and secondary ossification centers is called the epiphyseal line.

answer 3. Epiphyseal ossification: the events here are almost identical to vascular invasion except instead of forming compact bone spongy bone is formed. Also, hyaline cartilage is left on the ends of the bones (called articular cartilage) and the epiphyseal plates (growth plates) are also formed. The articular cartilage and epiphyseal plates are the only remains of the original hyaline cartilage model.

The adult long bones develops from three individual bones in the fetus: the diaphysis, or central shaft, and two epiphyses that form the end caps of the bone. Between these three bones is a thin layer of hyaline cartilage known as the epiphyseal plate or growth plate. Cartilage in the growth plate grows throughout childhood and adolescence to elongate the humerus and provide for the growth of the arm. The cartilage is replaced by bony tissue so that the long bone increases its length significantly while the growth plate remains relatively thin. Finally, at the end of puberty, the cartilage stops growing and is completely replaced by bone to form a singular, unified long bone. The region of bone between the epiphysis and diaphysis in the mature long bone is known as the metaphysis.

answer 4 Trabecular bone is a highly porous, heterogeneous, and anisotropic material which can be found at the epiphyses of long bones and in the vertebral bodies. Studying the mechanical properties of trabecular bone is important, since trabecular bone is the main load bearing bone in vertebral bodies and also transfers the load from joints to the compact bone of the cortex of long bones. At the macrostructural scale, the hard trabecular bone lattice, composed of trabecular struts and plates, forms a stiff and ductile structure that provides the framework for the soft, highly cellular bone marrow filling the intertrabecular spaces. At a microstructural scale, trabecular architecture is organized to optimize load transfer. Mineral and collagen content and architecture determine the mechanical properties of trabecular bone tissue.

In the appendicular skeleton, trabecular bone transfers mechanical loads from the articular surface to cortical bone, whereas in the vertebral bodies it represents the main load bearing structure. Bone tissue mechanical properties and architecture of trabecular bone are two main factors which determine the mechanical properties of trabecular bone. Fragility fractures that arise in the context of metabolic bone diseases such as osteoporosis usually occur in regions of trabecular bone

cortical bone trabecular bone Cortical bone, also known as compact bone or lamellar bone trabecular bone, also known as cancellous or spongy bone Cortical bone is much denser with a porosity ranging between 5% and 10% Trabecular bone is much more porous with porosity ranging anywhere from 50% to 90% Cortical bone is found primary is found in the shaft of long bones and forms the outer shell around cancellous bone at the end of joints and the vertebrae It is found in the end of long bones , in vertebrae and in flat bones like the pelvis The basic first level structure of cortical bone are osteons Its basic first level structure is the trabeculae

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