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Bone and Bones: A specialized Connective tissue that is the main constituent of the Skeleton. The principle cellular component of bone is comprised of Osteoblasts; Osteocytes; and Osteoclasts, while Fibrillar collagens and hydroxyapatite crystals form the Bone matrix.

Bone Remodeling

JoVE 10866

Bone remodeling is a continuous and balanced process of bone resorption by osteoclasts and bone formation by osteoblasts. In adults, it helps maintain bone mass and calcium homeostasis. While mechanical stress can stimulate turnover as part of the normal maintenance and reparative process, several hormones also regulate bone remodeling.

Parathyroid hormone (PTH) maintains homeostatic control of blood calcium levels by regulating bone resorption. PTH is released from the parathyroid glands in response to low levels of calcium in the blood. It stimulates osteoblasts to produce immune molecules that promote the differentiation of precursor cells into osteoclasts. Activation of osteoclasts promotes bone resorption, causing the mineralized bone matrix to break down and release calcium into the blood. When blood calcium levels are restored, a negative-feedback loop prevents further release of PTH. Osteoporosis is a disease in which bone resorption exceeds bone formation, resulting in reduced bone density. Osteoporosis is more prevalent in women, especially after menopause. This is due to the critical role played by the female sex hormone—estrogen—in bone remodeling. Estrogen limits the formation of osteoclasts and promotes their destruction via apoptosis. This ensures that bone formation is higher than bone resorption. However, estrogen levels decli

 Core: Biology

Bone Structure

JoVE 10864

Within the skeletal system, the structure of a bone, or osseous tissue, can be exemplified in a long bone, like the femur, where there are two types of osseous tissue: cortical and cancellous.

Covering the cortical, or compact bone, is a membrane called the periosteum, which contains connective tissue, capillaries, and nerves. The outer, solid layer—found along the diaphysis, the shaft—forms a dense protective shell around the medullary canal—the cavity that stores yellow bone marrow, composed primarily of fat cells. This space is also covered in a thin lining—the endosteum in which bone growth, remodeling, and repair occur. Within the dense layer of cortical bone are osteons—structural units, arranged in concentric rings called lamellae, that contain osteoblasts—cells critical for bone formation and growth. These cells eventually mature into osteocytes in the hollow space, the lacuna. Through the center of each osteon runs the Haversian canal, which contains more blood and lymphatic vessels, as well as nerve fibers. Towards the rounded ends of the long bone, the epiphyses is the second type of osseous tissue, known as the cancellous, or spongy, bone. This inner layer is composed of a honeycomb-like network of trabeculae—grouped arrangements that form along the lines of stress points to maximize strengt

 Core: Biology

What is the Skeletal System?

JoVE 10863

The adult human skeleton comprises 206 bones that are connected through cartilage, tendons, and ligaments. The skeleton provides a rigid framework for the human body, protects internal organs, and enables movement and locomotion. The human skeletal system consists of the axial and appendicular skeletons. Bone tissue is continuously built up and chewed away by specialized bone cells which are essential to overall health. Dysregulated bone cells and incorrect levels of chemical compounds in the blood lead to bone diseases. The axial skeleton consists of 80 bones and is divided into three regions: the skull, the vertebral column, and the rib cage. The upper portion of the skull—the cranium—consists of eight bones that enclose the brain, while the lower part consists of 14 bones. The vertebral column consists of 33 vertebrae: seven cervical, 12 thoracic, five lumbar, five fused sacral vertebrae, and four fused coccygeal vertebrae. The rib cage adds stability to the vertebral column and also protects the lungs and heart. It consists of 12 pairs of ribs, which attach to the thoracic vertebra via the costovertebral joint. The anterior portion of the rib cage attaches to the sternum—the flat bone at the center of the front of the chest—via the costal cartilages. The first seven ribs on each side are known as true ribs, as their cartilages

 Core: Biology

Computed Tomography and Optical Imaging of Osteogenesis-angiogenesis Coupling to Assess Integration of Cranial Bone Autografts and Allografts

1Skeletal Biotech Laboratory, The Hebrew University–Hadassah Faculty of Dental Medicine, 2Department of Surgery, Cedars-Sinai Medical Center, 3Board of Governors Regenerative Medicine Institute, Cedars-Sinai Medical Center, 4Biomedical Imaging Research Institute, Cedars-Sinai Medical Center

JoVE 53459

 Bioengineering

Visualizing Angiogenesis by Multiphoton Microscopy In Vivo in Genetically Modified 3D-PLGA/nHAp Scaffold for Calvarial Critical Bone Defect Repair

1Center for Translational Medicine Research and Development, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, 2Department of Orthopedic Surgery, Maastricht UMC+, 3Department of Orthopaedic Surgery, University Hospital RWTH, 4Research Laboratory for Biomedical Optics and Molecular Imaging, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences

JoVE 55381

 Bioengineering

Automated Quantification of Hematopoietic Cell – Stromal Cell Interactions in Histological Images of Undecalcified Bone

1Immunodynamics, German Rheumatism Research Center, a Leibniz Institute, 2Biophysical Analytics, German Rheumatism Research Center, a Leibniz Institute, 3Max-Delbrück Center for Molecular Medicine, 4Wimasis GmbH, 5Immunodynamics and Intravital Imaging, Charité - University of Medicine

JoVE 52544

 Developmental Biology
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