Original Editors - Candace Goh Show
Top Contributors - Lucinda hampton, Candace Goh, Admin, Shaimaa Eldib, Kim Jackson, Wataru Okuyama, Claire Knott, Manisha Shrestha, Khloud Shreif, George Prudden, Sai Kripa, Tony Lowe, Stephanie Geeurickx, WikiSysop and Joao Costa Bone is a metabolically active connective tissue that provides structural support, facilitates movement, and protects vital organs. Bone is composed of an extracellular matrix and bone cells (osteocytes)[1]. Under the right conditions, bone tissue undergoes a process of mineralization, formed by collagen matrix and hardened by deposited calcium. Bone is hard and many of its functions depend on that characteristic hardness.[2] The adult human skeleton is composed of 206 bones. At birth, there are approximately 270 bones, with the final adult count decreasing as a portion of these bones fuse during phases of skeletal growth and maturation. During life bone is constantly remodelling with most of the adult skeleton being replaced about every 10 years.[3] The skeleton is composed of both cortical bone (80%) and trabecular bone (20%).[4] Watch this 10 minute video on the skeletal system and why astronauts Scott Kelly and Mikhail Kornienko are out in space studying it. It also includes anatomy of the skeletal system, including the flat, short, and irregular bones, and their individual arrangements of compact and spongy [5] Bone Structure[edit | edit source]Bone consists of two types of tissue:
Bones also contain: Bone Types[edit | edit source]In the human body 5 bone types exist:
Gross Anatomy[edit | edit source]A long bone has 2 parts, the diaphysis and the epiphysis. Those bones that undergo endochondral ossification also have a physis (growth plate).
Bone Composition[edit | edit source]Bone is composed of cells and the extracellular matrix(ECM), which has both organic and inorganic substances. Osteoblasts synthesise bone ECM. The ECM consists of:
Bone Cells [edit | edit source]Bone cells make up about 10% of total bone volume. Bones are not a static tissue but need to be constantly maintained and remodeled. There are three main cell types involved in this process.
[edit | edit source]Bones are, in reality, living cells embedded in a mineral-based organic matrix. This extracellular matrix consists of:
Collagen gives bone its tensile strength, namely the resistance to being pulled apart. Hydroxyapatite gives the bones compressive strength or resistance to being compressed[7]. Bone marrow and Hematopoiesis[edit | edit source]Bone marrow is found in almost all bones where cancellous bone is present. Bone marrow is responsible for hematopoiesis, or the production of red blood cells, white blood cells, and platelets.[6] It of makes around 2 million red blood cells every second, as well as producing platelets, and white blood cells. Also, defective and old red blood cells are destroyed in bone marrow.[7][6] This 4 minute video explains Hematopoiesis: Formation of Blood Cells [11] Functional Unit of Compact Bone[edit | edit source]Osteon: structural unit of bone consisting of a haversian canal and corresponding lamellae of compact bone. Osteons represents a single functional unit of bone tissue. It is arranged with concentric lamellae of collagen fiber orientations around a central canal consisting of osteocyte’s arterial, venous, and nerve supply, is known as the Haversian canal. This system also consists of the canaliculi and Volkmann canal which allow for communication between neighboring osteocytes and communication between neighboring osteons, respectively. Osteons are several millimetres long and about 0.2 millimetre (0.008 inch) in diameter; they tend to run parallel to the long axis of a bone.[6] Mechanical Functions[edit | edit source]Skull gives protection to the brain Mechanical Functions
[edit | edit source]The metabolic functions of the bone are many:
Remodelling[edit | edit source]This is a physiological process in which old or damaged bone is removed by osteoclasts and then replaced by new bone formed by osteoblasts. There is a tight coupling of bone formation to bone resorption to ensure no net change in bone mass or quality after each remodeling. It requires coordinated action of the four types of bone cells. The process involves four major distinct but overlapping phases:
Watch this 8 minute video on bone remodeling . [13] Clinical Significance[edit | edit source]Bone tissue is susceptible to a myriad of pathologies that may range from etiologies of embryological, metabolic, autoimmune, neoplastic, or idiopathic origins. These include, but are not limited to, the conditions discussed below.
References[edit | edit source]
|