5. Objectives 6 & 7 Structural Unit of compact bone = osteon
Osteons (Haversian systems) are elongated cylinders oriented along bone axis
Several millimeters long
Osteon consists of concentric layers, called lamellae

7. Objectives 6 & 7
Lacuna(e) – cavity in the bone matrix where osteocyte reside. One osteocyte per lacuna
Canalicula – small canal connecting adjacent lamella to form a system of interconnected cavities
Haversian Canal – central canal of osteon containing blood vessels, lymph vessel and nerve
Volkmann’s Canal – canal connecting HCs to each other OR to the periosteum

10. Obj. 8 and 9
Ready… Go!
Finish for homework

11. Obj 8 & 9 Compact vs Spongy (Cancellous) Bone
Functional unit of compact?
Osteon
Functional unit of spongy?
Trabeculae
Location? Outer vs inner and ends

12. Obj 8 & 9 Compact vs Spongy (Cancellous) Bone
Compact stores minerals better (Calcium, etc.)
Spongy bone – marrow -> hematopoiesis
Spongy bone more porous = less calcium storage
More susceptible to osteoporosis

13. Obj 8 & 9 Three Types of Bone Cells
Osteocyte – most common cell in bone tissue
Avg life is 25 years – some MUCH longer
Mostly “inert”, but when destroyed, bones will be resorbed = bone loss
Many are formed from “trapped” osteoblasts

14. Obj 8 & 9 Three Types of Bone Cells Osteoblast – “makes bone”
Work in ‘groups’
Produce hydroxyapatite
Usually, eventually turn into osteocytes

15. Obj 8 & 9 Three Types of Bone Cells Osteoclast – “breaks down bone”
Critical in bone resorption for growth
Secrete and acid and collagenase to break down bone