Bones
Anatomy and Structure
Bones are rigid organs that constitute part of the endoskeleton of vertebrates. They provide structure to the body, assist in movement, protect various organs, produce red and white blood cells, and store minerals.
Bones are composed of two types of tissue: compact bone and cancellous bone. Compact bone, also known as cortical bone, forms the hard outer shell of all bones. It is dense, strong, and contains few spaces. Cancellous bone, also known as trabecular or spongy bone, is found inside bones and is softer and less dense than compact bone. It has a honeycomb-like structure with numerous small spaces that are filled with red bone marrow, where blood cells are produced.
Bone Cells
There are four types of cells in bone: osteoblasts, osteocytes, osteoclasts, and bone lining cells. Osteoblasts are responsible for the formation of new bone, osteocytes maintain the bone matrix, osteoclasts break down bone, and bone lining cells cover the surface of bones.
Bone Formation and Growth
Bone formation, or ossification, begins in the embryo and continues into young adulthood. There are two types of ossification: intramembranous ossification, which forms flat bones like the skull and clavicle, and endochondral ossification, which forms long bones like the femur and humerus.
Bone growth occurs at the epiphyseal plate, or growth plate, located at each end of long bones. As children grow, new bone is added at the epiphyseal plate, causing the bone to lengthen. Once a person reaches their full adult height, the epiphyseal plate closes and is replaced by solid bone.
Bone Remodeling
Bone remodeling is a lifelong process where mature bone tissue is removed from the skeleton by osteoclasts and new bone tissue is formed by osteoblasts. This process is necessary to maintain the structural integrity of the skeleton, repair micro-damage, and regulate calcium homeostasis.
Bone Diseases and Conditions
There are numerous diseases and conditions that can affect the bones, including osteoporosis, osteogenesis imperfecta, Paget's disease, and bone cancer. These conditions can lead to a decrease in bone density, an increase in bone fragility, abnormal bone growth, and severe pain.