Bone Tissue Objectives
1. List and describe all cell types, fibers, and components of the ECM of bone.
a. Cells
i. Osteocytes-mature bone cell. Are in lacunae surrounded by
calcified ECM. Have cytoplasmic processes that extend
through canaliculi and contact other osteocytes for
communication and material transport
ii. Osteoblasts-immature non dividing cells that actively lay new
extracellular matrix. Simple cuboidal; basophilic
iii. Osteoclasts-multinucleate cells (2-70) that release carbonic
anhydrase to dissolve the mineral component of the ECM. Also
release collagenase and hydrolase to dissolve the fibers of the
ECM. Osteoclastic activity takes place on a specialized surface
called the ruffled border and is contained by the sealing zone,
which flanks the ruffled borders and is rich in integrins to seal
the subosteoclastic compartments environment in.
iv. Osteoprogenitor cells-unidentifiable cells that give rise to
osteoblasts
v. Bone Lining cells-cells that line all bone tissue. They are
involved in stress sensing and they seal the bony tissue from
the outside world (protect microenvironment)
b. Fibers
i. Type 1 Collagen
c. Components
i. Organic matrix
1. Low in proteoglycans therefore low in water content
2. Three predominant glycoproteins
a. Osteonectin-bind osteocyte to extracellular
matrix
b. Osteocalcin-binds calcium to the ECM
c. Bone Sialoprotein (Osteopontin)ii. Inorganic matrix
1. Hydroxyapetite Crystals
2. List and describe components of the organic and inorganic matrix
a. Inorganic
i. Hydroxyapetite protein
b. Organic
i. Type I Collagen
ii. Osteonectin
iii. Osteocalcin
iv. Bone Sialoprotein
3. List and describe the individual components of bone
4. Identify and describe the structural and functional unit of the two types of
bone
a. Compact Bone
i. Osteon
b. Trabecular Bone
i. Trabecular Packets
5. Describe the morphological organization of spongy and compact bone tissue
a. Osteons are in compact bone tissue. They are concentric rings of
osteocytes and surrounding ECM. There is a central canal that houses
the blood vessel that delivers the nutrients to the osteocytes
b. Trabecular packets are in Trabecular bone. They are composed of
sheets of lamellar bone that arrange in a triangular pattern. They
receive their nutrients through the marrow.
6. Vascular supply is achieved through Volkmann and Haversian Canals. The
haversian canals are run through the osteons and are surrounded by
concentric rings of osteocytes and extracellular matrix. The nutrients are
diffused through the osteocytes by way of the cytoplasmic processes in the
canaliculi. This limits the size of the osteons to .2mm in diameter. The
vessels in the Volkmann canals supply the vessels in the haversian canals.
They traverse osteons and bring in nutrient rich blood and export waste
products.
7. Bone is quite vascularized through out the tissue. Cartilaginous tissue is
avascular and relies wholly on diffusion. Through the extracellular matrix.
Nutrients must difuse through the osteocytes, however this is much easier
because of the cytoplasmic processes that are present bony tissue.
8. List and describe how different terminology is used to describe structure and
function of bone tissue.
9. Bone has two major functions: Providing structure, and acting as a mineral
reservoir.
10. Relate the morphology of bone with its function
11. List and describe the theories of mineralization
a. Cellular Nucleation Theory
i. Bits of cytoplasm pinch off in vesicles and secrete alkaline
phosphatase. Alkaline Phosphatase cleaves pyrophosphate
(PPi inhibits calcification, therefore inhibition of PPi would
allow for calcification to initiate)
b. Macromolecular nucleation Theory
i. Multiple Macromolecules are involved
1. Collagen
2. Chondrocalcin
a. Bind Calcium to ECM
3. Osteocalcin
a. Bind Calcium to ECM
4. Sulfated Proteoglycans
a. Releases Calcium needed for calcification
12. Define, describe and differentiate between the process of ossification,
calcification and growth.
a. Ossification I the overall process of bone formation.
b. Calcification is the impregnation
c. Bone Growth=Ossification
13. Describe the process of internal remodeling of bone and its structural basis.
14. Know when remodeling first starts and when its stops in the body.
Understand how parathyroid hormone and calcitonin help control the
internal remodeling process
a. Parathyroid Hormone responds to Low Calcium and therefore will
upregulate bone resorption. Binding sites are on the osteoblasts,
which will then secrete Osteoclast Stimulating Factor.
b. Calcitonin responds to High Calcium in the blood and will upregulate
bone formation. Receptors are on the osteoclasts.
15. Describe the function of structural and metabolic bone. Be able to relate it to
structures we see in bone
16. Know the relative Rates of bone tissue turnover.
17. Describe the morphology of trabeculae and their remodeling