1. Skeletal System Study of system began in 2 nd century – Galen By 18 th century system was completely described

2. Q: How many bones are there in an adult human? Skeletal system develops from the middle germ layer: Mesoderm [all but facial bones, which are derived from ectoderm] Development begins in the first few weeks after fertilization by 3 rd month there are 600 distinct bones At birth there are 450 distinct bones By age 25 all skeletal growth is completed A: 206

3. As bones grow & form their proportions change At birth: the head is as big around as the chest and ¼ of the body’s length Adult: the head is ½ as big around as the chest and 1/7 of the body’s length

4. Functions of the Skeletal System Support Protection Movement Storage: minerals fat Hemopoiesis [hematopoiesis]

5. 2 Major Divisions of Skeleton 80 bones - form vertical axis of body Skull -28 Vertebral column- 26 Ribs/sternum- 25 Hyoid bone -1 126 bones – free appendages and their attachments to axial skeleton Upper Extremities- 60 Lower Extremities – 60 Pectoral Girdles – 4 Pelvic Girdle - 2 Axial Skeleton Appendicular Skeleton

7. Bones come in different shapes Long = longer than wide Short = just as wide as long Flat = thin, flattened shape – usually curved Irregular = don’t fit into any of the above categories Sesamoid = small, round – grow in certain tendons where there is considerable pressure Wormian/sutural = small bones at joints of random cranial bones

8. Bone is Connective Tissue Cells in a Matrix Matrix = collagen & proteoglycans & calcium salts –primarily calcium phosphate Compact/dense Cancellous/spongy Cells = osteocytes, osteoblasts & osteoclasts *highly vascularized

9. Bone Cells are responsible for the integrity of bone tissue = very dynamic tissue Osteocytes = maintain bone tissue – live in spaces called lacunae. Connected by canaliculi Osteoblasts = form new bone tissue [ossification/osteogenesis] Osteoclasts = break down bone tissue REMODELING of bone = constant activity.

10. Blood Vessels Within compact bone there is an osteon which contains the Haversian or central canal – runs on long axis of bone Running perpendicular are Volkmann’s or perforating canals

11. Spongy Bone does not have osteons. It has trabeculae [ plates of bone tissue in an irregular pattern] Short and Flat bones are primarily made of spongy bone, with coverings of compact bone Spongy bone has openings in trabeculae filled with red bone marrow

12. General features of bones Long bone = composite bone Diaphysis = shaft Epiphysis = expanded portion at end of diaphysis. Covering the end is Articular Cartilage. Where the two meet is called the Epiphyseal Plate [growth plate]. Becomes the Epiphyseal Line. Within diaphysis is a hollow space called: Medullary cavity

13. Outer surface of all bones have Periosteum: rich with nerve fibers, lymphatic vessels, blood vessels and osteoblasts Inner surface of all bones have Endosteum: osteclasts Blood vessels enter bone tissue via Nutrient Foramen [foramen =hole or opening] In addition to foramen, bones have many surface markings and characteristics that make each bone unique. [i.e. holes, depressions, smooth facets, projections]