muscles Flashcards
What is the double meaning of bone
Bone is an organ, and organs are made up of different types of tissues
Bone can also mean the tissue, and one of the tissues found in the bones of the skeleton
What are the 6 functions of the skeletal system
1) Support,
2) Protection
3) Movement
4) Calcium and phosphorus reserve
5) Haemopoiesis
6) Fat storage
Axial skeleton
80 bones
(some are paired)
It has an emphasis on support/protection and haemopoiesis
Appendicular skeleton
126 paired bones
Movement
Fat storage
Endosteum
thin, inner fibro-cellular layer lining medullary cavity
Periosteum
Outer fibro-cellular sheath surrounding the bone
What is the extracellular matrix made of
Fibres (the organic component) Ground substance (the inorganic component)
What are the fibres in bone and give their precise function
Fibres resists tension/stretching and pulling
The ones in bone are Type I and V
Ground substance in bone and function
Resists compression
squeezing/crushing
Osteogenic cells
surface of bone in the periosteum and endosteum
Also found in the central canals of compact bone.
It normall is dormant but can divide and supply developing bone with bone forming cells
Osteoblast
Usually in a layer, under the peri or endosteum wherever new bone is being formed
it is needed for the synthesis, deposition and calcification of the osteoid
Osteoid
The organic extracellular matrix of bone, synthesised by osteoblasts prior to mineral deposition
What is osteoid primarily made of
it’s 70% collagen with the remainder consisting of proteoglycans, other proteins and water
This precursor matrix is eventually infiltrated with bone salts (hydroxyapatite) and this process is called calcification
What is the significance of the osteoid calcification
It prevents nutritive fluids from diffusing freely through it
Osteocyte
Trapped within the lacunae inside of bone.
Osteocytes can communicate with neighboring cells through their long cellular processes inside canaliculi
they are required for
Bone tissue maintenance
they contibute to lattice inside the bone
responsible for localised minor repair
Rapid Calcium exchange
An Osteoclast is a syncytium
A fusion of monocyte progenitor cells
They are found at sites where bone resorption is occuring
and secrete acid and enzymes, dissolves the mineral and organic components of bone
How does the bone grow
Appositional growth+resorption
Collectively called bone remodelling.
Why can’t the bone grow via interstitial growth
Because Bone is too rigid.
Interstitial growth involves cells dividing inside the tissue, secreting more Ecm AND GROWING THE TISSUE FROM WITHIN
Bones also can’t do that because bone i is designed to resist deformation, so it can only grow by adding new bone onto an existing surface
Endochondral ossification
Ossification: Plate of hyaline cartilage (epiphyseal plate) which undergoes interstitial growth. As plate grows thicker, cartilage near the
metaphysis dies. This provides the framework for new bone to grow into, through the process of osteoblasts putting down new bone. As you reach the
age of 16-19, the rate of cartilage death exceeds rate of hyaline cartilage growth, and the metaphysis catches up. It becomes in contact with the epiphysis
and fuses forming the epiphyseal line. This determines your height.
How are secondary osteon formed
1) Osteoclasts form and gather in an area that needs to be remodelled. This group of osteoclasts starts boring its way through the existing bone. This area is called the “cutting cone, and creates a tunnel inside the existing bone. This is how secondary osteons differ to primary osteons. In primary osteons the tunnel is created on the surface of a bone as it grows.”
After the tunnel has been created, osteoblasts mve in and line the tunnel wall. They form the new active endosteum and start depositing osteoid onto the walls of the tunnel. The osteoid layer is then calcified, forming new lamella. A blood vessel will grow into the newly formed tunnel to supply the cells
Osteoblasts deposit layer upon layer of new concentric lamellae onto the walls of the tunnel, slowly filling it in. This active area behind the cutting cone is called the closing cone. Some of the osteoblasts are trapped in the newly deposited lamellar bone and become osteocytes
Eventually the tunnel is reduced to the size of a typical haversian canal. The remaining osteoblasts lining the Haversian canal either die or become bone lining cells and contribute to the resting endosteum. A new osteon is now formed. Sometimes a line can be seen at the junction between the outermost lamella of the new osteon and the pre-existing older bone-called the cement line
