so bone is not completely solid but has many small spaces between its cells and the components of the extracellular Matrix some spaces serve as channels for blood vessels that supply bone cells with nutrients other spaces act as a storage site for red bone marrow now depending on the size and the distribution of the spaces between the cells and the components of the extracellular Matrix these regions of Bones can be classified as either compact bone or spongy bone so compact bone which can also be referred to as cortical bone contains few spaces between bone cells and the components of the extracellular matrix it's found beneath the periosteum of all bones and it makes up the bulk of the diaphysis or that shaft of a long bone compact bone is strong and provides protection and support it also resists the stresses produced by the weight of gravity and of movement now compact bone is composed of repeating structural units called an osteon so this is an osteon here this is another one here here and here each osteon consists of concentric Lal arranged around a central Canal so the concentric Lal a circular plates of mineralized or calcified extracellular matrix of increasing diameter so it's this ring here and then here and then here and then here each layer is a ring of entric Lal these concentric Lal circle around what we call a central Canal which is like a little tunnel which runs through the center of an osteon and contains our blood vessels and our nerves the central Canal of an osteon tends to run parallel to the long axis of a bone now between our concentric Lal a small spaces called Lun a Luna with no e on the end is the singular and these are small spaces surrounded by The extracellular Matrix which now contain an Osteo site so remembering we have our Osteo blasts which secrete that osteoid or the extracellular Matrix they secrete it all around itself when that osteoblast becomes trapped in that extracellular Matrix in the space called the Lacuna we now turn that cell the Osteo site now radiating in all different directions out from that osteocyte are the osteocytes processors and they run through little channels called the canicula the canicula connect the LUN with one another so the Osteo sites can communicate as well as with a central Canal forming an interconnected network of canals throughout the bone this system provides many roots for the nutrients and the oxygen to read the osteocytes as well as for the removal of waste lastly blood vessels and nerves from the periosteum so remember the tissue that surrounds our bone penetrate into the compact bone through transverse Perforating canals you may also see these termed vulcan's canals the vessels and the nerves of the Perforating canals will connect with those of the Maller cavity of the periosteum and of the central Canal so again recapping some of those structures for you which I do want you to be able to to identify on an image and provide a function so an osteon is that compact cylinder of concentric Lal and it's the structure that makes up compact bone so very important that we know that osteons make up compact bone our concentric lame are the circular rings of calcified extracellular matrix and those rings are what forms the osteons the central Canal is that small tunnel which runs through the center of the osteon it houses both our blood vessels and our nerves the laun are the small Hollow spaces between the concentric lalet which hous the Osteo site the Osteo site we've already talked about it's our mature bone cells that sit within the Lacuna they monitor and maintain metabolism of bone tissue the canicula are those thin channels containing the processes of the osteocytes they connect the different Lacuna so that the osteocytes can communicate with one another and then the perating or the vulcan's canal connect the vessels and nerves of the periosteum the meler cavity and the central canals spongy bone which is also referred to as Canalis bone is always located in the interior of the bone protected by a layer of compact bone instead of osteons it's made up of Lal arranged in an irregular pattern of thin columns which we call Tula between the tabula are spaces that are visible to the naked eye so you can see the gaps in between those tabuli and those spaces are filled with red bone marrow in bones that produce uh blood cells and then yellow bone marrow in the other bones so somewhat like oion each tabula consists of our concentric Lal it has osteocytes in the Lacuna and canicula connecting the osteocytes now at a glance the order or the structure of the tracula of spongy bone tissue appears quite unorganized especially compared to the tight compact structure of the osteons of compact bone however they are actually deliberately orientated along lines of stress a characteristic which helps bone resist stress and transfer Force without actually breaking or snapping in half now spongy bone tissue tends to be located where bones are not heavily stressed but where stressors are applied from many directions so whereas compact bone is thickest under high levels of force or weight bearing and where the line of stress is from only one angle so for example the gravity the weight of gravity is kind of only moving downwards the spongy bone will be placed in a part of the bone where it could be pulled in all different directions now although it's not as strong as compact bone spongy bone tissue helps lighten the overall weight of a bone which is important we don't want our skeleton so heavy that we actually struggle to move and spongy bone tissue also plays an important role in supporting and protecting the red bone marrow which is where our blood cell production occurs