Anatomy of Skeletal System Flashcards
Endochondral Ossification
- Bone originates as a cartilage model
- Cartilage is a flexible connective tissue found in many areas of the body
- Chondrocytes are the only cells found in healthy cartilage
- They produce and maintain the cartilaginous matrix, which consists mainly of collagen
Stages of endochondral ossification
STAGE 1
- The chondrocytes begin to increase in size while the matrix calcifies around them
- These chondrocytes become starved and therefore die
STAGE 2
- Blood vessels grow into the perichondrium
- Cells in the perichondrium differentiate into osteoblasts (bone forming cells) and begin forming bone around the edge of the cartilage shaft
- This is now termed the periosteum
STAGE 3
- Blood vessels and fibroblasts migrate into the cartilage. The fibroblasts differentiate into osteoblasts
- The calcified cartilage matrix breaks down and is replaced by trabecular bone
- The site where this first occurs is known as the primary ossification centre
STAGE 4
- The wave of ossification spreads towards the ends of the long bone
- Osteoclasts (bone resorbing cells) absorb bone from the centre leaving a marrow cavity
- Bone grows inwards from the periosteum forming the compact bone surrounding the marrow cavity
STAGE 5
- Capillaries and osteoblasts migrate into the epiphyses and ossification begins
- These areas are now known as secondary ossification centres
- The timing of the appearance of secondary ossification centres varies greatly
Immature Long Bone
- Formation of trabecular bone in epiphysis leaves two areas of cartilage
- An articular cartilage
- Articulates with cartilage from another bone, prevents bone on bone articulations
- An epiphyseal growth plate
- Allows interstitial growth in the bone
Growth of cartilage
Growth of Long Bones
Factors that Affect Bone Development
- Genetic- The overall shape and dimensions of a bone are determined genetically
- Activity- Bone adapts to meet functional demands
- Nutritional- Availability of calcium, phosphate salts, vitamins A, C, D, K and B12 are essential for normal bone development
- Hormonal- Several hormones, including calcitocin, parathyroid hormone, growth hormone and sex hormones can affect calcium levels and bone growth
- Pathological- Disease processes, such as infection, bone tumours and tuberculosis can affect bone growth
- Aging- Loss of calcium and the ability to utilise it causes ‘brittle bones’ which easily fracture
Axial skeleton
Appendicular skeleton
Classification of Bone by Shape
Bones may be classified on the basis of their mode of ossification.
Another classification is based on the shape of the bones:
- LONG BONES: have elongated tubular shafts, a central medullary cavity and expanded ends for articulation. e.g. Femur, Humerus, Tibia
- SHORT BONES: are typically constructed of a thin outer shell of compact bone with an interior completely occupied by cancellous bone. e.g. Carpus (Hand) and Tarsus (Foot)
- FLAT BONES: are typified by bones of the vault of the skull, where the structure consists of two shells of compact bone (termed inner and outer tables) separated by a layer of cancellous bone (diploe). e.g. Frontal and Parietal bone, Sternum and Ribs.
Located within the joints of between some of the flat bones of the skull, small clusters or isolated bones sometimes occur. These are termed WORMIAN or SUTURAL bones, and are inconsistent in number.
- IRREGULAR BONES: anything that will not fit into the other categories! e.g. Sphenoid bone of the skull
- SESAMOID BONES: formed in a tendon (e.g. Patella)
Anatomical Terms Applied to Bones
Vertebral column
Curvatures of Vertebral Column
Scoliosis
Abnormal lateral curvature
Most common deformity
Occurs mostly in thoracic region
May be developmental, in which the body and arch of the vertebrae fail to develop on one side
Can be corrected with a back brace if detected early enough
How many bones in the skull?
