what are the skeletal system functions
how does flat bones form
formed in direct ossification
how does long bones form
formed by indirect ossification but in a multi stage process
how does short and irregular bones form
formed by indirect ossification where a carilage moel is created greadually dissolved and then replaced by bone
ossification steps
1- caritalage model grows
2- cartilage replaced by bone
3- ossificationcomplete (articular cartilage remains)
what is the bone composition
what is the bone structure function
1- tubular constrcution of compact bone in the shaft
2- light, cancellous bone at the ends
3- efficent arrangement of strusts and ties in cancellous bone to minimize weight
where are osteoblasts formed
formed in the periosteum tight band of organic material
compact bone
dense and located in the shaft of the long bone
spongy bone
forms the holes in the bone
- holes filled of liquid to help form red blood cells
flat bone
have spongy and compact bone
bone repair
1- Haematoma formation
2- Granular material formation
3- Hard callus formation
4- Remodelling
Haematoma formation
After fracture, blood vessels in the bone and periosteum are torn and begin to hemorrhage. As a result, a haematoma (mass of clotted blood) forms at the site. Bone cells (deprived of nutrients) begin to die and the tissue becomes inflamed, swollen and painful
Granular material formation
Within a few days soft granulation tissue (soft callus) forms. This is caused by: • invasion of capillaries • phagocytic cells clean up the debris • fibroblasts migrate into the site and fill the area with collagen • osteoblasts migrate into the site from the periosteum and begin bone formation
Hard callus formation
The activity of osteoblasts causes new trabecular (spongey) bone to form within the soft callus. Hard callus formation begins 3 - 4 weeks after injury and continues for 2 - 3 months.
Remodelling
Remodelling begins during the hard callus stage and continues for several months. The excess material around the fracture site is removed, as well as from within the medullary cavity. Compact bone is laid down to reform the shaft walls.
what happens with a persons bone composition as they age
The 1 : 2 ratio of organic material : inorganic salts provides our skeleton with certain mechanical characteristcs. At birth the ratio is 1:1 and when an elder the composition is 1:7
long bones have evolved in 2 ways
- perform speedy movements
what is the bone composition
- 30-40% collagen: stiff and strong: resist tension forces (forces that pull the bone apart and ground substances)
explaint the stess strain curve
name the 4 type of forces
1- compression: longitudinal forces
2- tension: pulling the bone apart
3- shearing/bending: transverse forces
4- torsion: rotation
The two conflicting roles of weight support, yet
lightness in construction of bones are met by:
compression strenght vaires dependant on what
tension forces