September 27, 2011
Lecture 7 – Bone Part 2
The osteon is the that compact bone is organized, how we can end up with dense
concentration of matrix.
It causes compressional strength from running parallel to long axis
Matrix forms the lamella. Osteocytes exist between lamellae within lacunae. As cells
surround themselves with matrix, they leave a little space for cell processes to exist in,
known as canaliculi. Canaliculi allow for cells processes to meet with one another
communicating through gap junctions. Creates little tunnels that join to the central canal.
Allows for movement of material and nutrients from veins, arteries and nerves to reach
remote cells away from central canal.
Matrix strengthened by alternating orientation of collagen fibers.
Compact bone forms the cortex of all bone
Deep within is spongy bone. Inner surface is covered with spongy bone. Bone matrix
forms trabeculae (chocolate part of an Aero bar) but is lamellated with matrix again.
Again there are lacunae within there again except there are not osteons and central canal.
There are canaliculi that join the cells of deeper layers and more superficial layers.
Canaliculi open at the surface (pinholes). Spaces within spongy bone are filled with red
bone marrow (blood) so canaliculi allows for diffusion of nutrients without the use of
Surface of spongy bone is covered by a layer called endosteum (perichondrium for
compact bone). Just a layer of cells on the internal surface of bone, no fibers. Cells like
osteoclasts, osteoblasts (matrix surface cells). If there is an internal surface of bone organ,
it will be covered by endosteum. It is busy because osteoclasts resorbing bone and
osteoblasts laying down bone.
Red marrow fills spaces
Why do we want them organized two ways? Compact and spongy.
Compact bone is very dense and heavy. We use as much compact bone as we need to
withstand forces and the remainder will be spongy bone
Compact bone is able to withstand in one axis. Spongy bone is able to withstand pressure
along multiple axis, trabeculae is oriented along multiple axis.
Bone that withstands stresses along multiple axes is endowed with more spongy bone,
withstanding only one force is compact bone. There can be mixture like long bone where
epiphysis has spongy bone and diaphysis has more compact bone.
Matrix stains very pink, acidic (eosinophilic).
Periosteum consists of 2 layers like perichondrium. It has a superficial fibrous layer
(capsule made up of dense irregular CT). There is a deep cellular layer. Fibers in the
periosteum are cemented into the matrix of more superficial lamellae and anchors collagen fibers. Periosteum is bound down tightly. Perforating (Sharpey’s) fibers are in
places where tendons and ligaments attach to bone.
Periosteum and joint capsules are both dense irregular CT (sheet-like covering joint or
bone). Tendons and ligaments are dense regular CT because they withstand stresses along
There are a lot of perforating fibers for tendons and ligaments attachment to bones.
Tendon (collagen type I) intermingle with collagen type I fibers of the periosteum. It is
not sticking of one structure to another but coming together and makes a continuation of
one structure to another.
Periosteum is very reactive, and will participate in the repair of the fracture, etc. It will be
more rapid. Fractures are easier to repair than tearing of periosteum. Periosteum can also
lay down bone.
Endosteum lines all internal surfaces. Ma