Skeletal System
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Transcript of Skeletal System
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Skeletal System
• Study of system began in 2nd century
– Galen
•By 18th century system was completely described
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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 3rd month there are 600 distinct bones
• At birth there are 450 distinct bones• By age 25 all skeletal growth is completed
A: 206
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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
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Functions of the Skeletal System
• Support• Protection• Movement• Storage: minerals
fat• Hemopoiesis [hematopoiesis]
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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
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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
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Bone is Connective Tissue
Cells in a MatrixMatrix = collagen & proteoglycans &
calcium salts –primarily calcium phosphate
Compact/dense Cancellous/spongyCells = osteocytes, osteoblasts &
osteoclasts*highly vascularized
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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.
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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
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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
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General features of bonesLong 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
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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]