Bone Biology

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Human Skeleton 9/12 Notes
Bone Biology
Bone Biology
* Bone is both a tissue and an organ. It is a specific type of biological tissue with its own unique chemical and molecular structure. Bone is a unique combination of organic and inorganic components. * Two levels of study

* Macroscopic: gross morphological features
* Microscopic: aka histology, study of tissues
* Two levels of histology
* Cellular
* Molecular
Bone Biology – Macroscopic
* All bone in adult skeleton is found in two basic configurations: * Compact (cortical) bone
* Very dense
* Seemingly solid bone
* Found on outer surface of all bones
* In tubular (long and short) bones it is concentrated on walls of shafts * Subchondral bone is a variant of compact bone found at joints and covered by cartilage during life, it is smoother and shinier and lacks osteons and haversian systems * Cancellous (spongy, trabecular) bone

* More porous
* Honeycomb structure
* Formed by bony columns (trabeculae) separated by large spaces * Found: under joint surface, at ends of tubular bones, inside flat bones (skull), inside vertebral bodies, at insertion sites for large tendons * Molecular and cellular structure identical in cancellous and compact bone * Only difference is porosity and distribution

* Components of tubular bones, described according to centers of ossification * Diaphysis (shaft): main portion of tubular bone, primary ossification center of the bone * Epiphysis (ends): form joint surfaces, secondary ossification center of the bone * Metaphysis: expanded, flared ends of shafts, site of growth plates and fusion of diaphysis and epiphysis * Forces acting on surface of tubular bone

* Diaphysis (hollow tube with thick walls): good as a solid cylinder for resistance and weight bearing, the thicker the cortical walls the stronger the cylinder * Epiphysis (joint surfaces): forces applied over a broad surface in variable directions, larger joint surfaces mean transmission of greater forces throughout joints * Forces acting on internal aspect of tubular bones

* Trabeculae (thin, bony spicules that form the trabecular/cancellous bone): more economical in transmitting and resisting stress, concentrated along direction axes of greatest force * Wolff’s Law: based on premise that bone is a costly organ to develop and maintain * Julius Wolff – 19th century German surgeon is the creator or Wolff’s law, aka Law of Bone Transformation * Bone is a dynamic, highly vascularized tissue capable of changing shape during lifetime (remodeling) * Changes are a response to mechanical demands/stresses/loads placed on it * Improves capacity to resist external loadings

* Bone is deposited where it is needed and resorbed where it is not Bone Biology – Hematopoiesis (Def: formation of blood cells in the living body) * Diaphysis is comprised of cortical walls and medullary cavity (hollow inside shaft of bones) and the epiphysis is comprised of trabecular cone with thin cortical shell but both contain marrow and are sites of red blood cell formation * At birth, all bone marrow is red (hematopoietic) marrow * During the growth process some of this is replaced with yellow (fatty) marrow * In adults, hemopoetic marrow remains in flat bones and epiphysis of tubular bones Bone Biology – Joints

* Musculoskeletal systems is a series of bony levers operated by muscles * Connections between bony elements are joints
* Bones articulate with one another at joints
* They are connected to each other by ligaments and cartilage * Movement at joints limited by shape of the articular surfaces and strength of attachment ligaments * Three main categories of joins

* Synovial joints: freely moving joints, joined by hyaline cartilage * Cartilaginous joints (synchondroses): very little movement possible, joined by cartilage (hyaline or fibrocartilage)...
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