c.v.2.c. Mesenchymal stem cells c.v.2.d. Osteoclasts c.v.2.d.i. Tear down bone c.vi. Endosteum c.vi.1. Lining of cells (lines the medullary cavity – same thing as the inner layer of periosteum) c.vi.2. Made up of the 4 cells in the periosteum (osteoblast, osteoclast, mesemchymal, osteoprogenators) c.vi.3. Lines the inside of the medullary cavity, lines the surface of the spongy bone, and lines haversion canals. c.vii. Flat Bone Structure c.vii.1. Diploe c.vii.1.a. Spongy bone found in cranium bone (sandwiched)
c.vii.2. Hematopoiesis c.vii.2.a. Occurs mostly in the pelvic bones and the cranial bones c.vii.2.b. The making of blood cells c.vii.2.c. Sternum, skull and pelvis are major sites of this 2. Microscopic Bone Structure a. Matrix of bone a.i. Hydroxyapatite salt crystals and type 1 collagen a.ii. Hydroxyapatite is inorganic (2/3)and type 1 collagen is organic (1/3) a.iii. If you make a substance very hard, you make it brittle (it can break very easily) a.iv. Type 1 collagen can bend easily but can’t stretch very well (high tensile strength). Its hard substance but it’s not very brittle. a.v. Hydroxyapatite is very brittle a.vi. Brittle bone disease a.vi.1. Too much hydroxyapatite production so bones are very brittle so if they crash into a wall their bones will shatter. b. Cells of the Bone b.i. Osteoprogenitor cells becomes osteoblast then becomes osteocytes in a lacunae after it makes its matrix b.ii. Osteoclasts is a macrophage that eats bones b.iii. The battle of the bone b.iii.1. Osteoblasts vs. osteoclasts b.iii.1.a. Build your bone up and degrading bone b.iii.1.b. At one point of your life (early) osteoblasts win and later in life osteoclasts wins b.iii.2. Osteoprogenitor cells b.iii.2.a. They become into osteoblasts make bone matrix
b.iii.2.b. They are found in the inner cellular layer of the periosteum and the endosteum b.iii.2.c. Endosteum can be found lining the medullary cavity, lining the inside of the Haversion canals, and lines the surface of the spongy bone (trabeculae) b.iii.2.c.i. Can be called incomplete cell layer b.iii.2.d. Bone can grow appositionally because of the presence of endosteum b.iii.2.e. Why can’t bones grow interstitially? b.iii.2.e.i. The matrix is too hard, can’t move around in the matrix b.iii.2.f. Osteoblasts b.iii.2.f.i. Found on the surface of bone, find them in the endosteum and the inner cell layers of the peristeum b.iii.2.f.ii. Secretes type 1 collagen and then the cell will drip the hydroxyapatite b.iii.2.f.iii. Spongy bone doesn’t develop from cartilage but develops from mesenchymal stem cells. intramembranous ossification. b.iii.2.f.iv. Have receptors for a hormone called PTH (parathyroid hormone) b.iii.2.f.iv.1. When blood calcium levels are too low, parathyroid glands will secrete PTH into your blood into the bone marrow which will tell the osteoblasts to release OSF (osteoclast stimulating factor) which binds to osteoclast thus, increasing the activity of osteoclasts which will be ripping the bone apart and then calcium spits into your blood.