The Skeletal System

Essentials of Human Anatomy & Physiology

Elaine N. Marieb

Chapter 5 Introduction The Skeletal System The Skeletal System  Composed of  Bones  Cartilage and Ligaments  Blood (vessels and marrow)  Nerves  Framework/Support Functions of  Protection of vital organs Bones  Skull  Ribcage  Levers for movement  We don’t move our bones; we move our muscles and they pull the bones.  Storage  Minerals Ca & P  Fat  Blood cell formation Bones of the Human Body  The ADULT skeleton has 206 bones  4 Main classification of bones based on SHAPE. Long Short Flat Irregular Classification of Bones on the Basis of Shape

Figure 5.1

 Long bones  Typically longer than wide  Have a shaft with heads at both ends  Contain mostly compact bone  Examples: Femur, humerus Classification of Bones

 Short bones  As long as they are wide  Generally cube-shape  Contain mostly spongy bone  Examples: Carpals, tarsals Classification of Bones

 Flat bones  Thin and flattened  Usually curved  Thin layers of compact bone around a layer of spongy bone  Spongy bone sandwich with compact bone bread  Examples: Skull, ribs, sternum Classification of Bones

 Irregular bones  Irregular shape  Do not fit into other bone classification categories  Example: Vertebrae and hip Classification of Bones  “Other” categories  Sesamoid  Bone buried in a tendon  Example : patella (kneecap)  Sutural  Bone found between flat bones in skull  Formed to “fill in” gaps between the bones as they fuse together during infancy and childhood

Bones of the Human Body  Two basic types of bone tissue  Compact bone  Homogeneous/Even Appearance  Spongy bone  Small needle-like pieces of bone  Many open spaces

Figure 5.2b Gross Anatomy of a Long Bone  Diaphysis  Shaft - middle  Composed of compact bone  Epiphysis  Heads - Ends of the bone  Composed mostly of spongy bone Figure 5.2a Structures of a Long Bone  Epiphyseal plates allow for growth of long bone during childhood  New cartilage is continuously formed as older cartilage becomes ossified (hardens)  Medullary cavity  Central cavity of the diaphysis/shaft  Contains yellow marrow (mostly fat) in adults  Contains red marrow (for blood cell formation) in infants/children

Figure 5.2a Structures of a Long Bone

 Articular cartilage  Covers the external surface of the epiphyses  Made of hyaline cartilage  Decreases friction

at joint surfaces Figure 5.2a

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 5.8a Types of Bone Cells  Osteocytes  Mature bone cells  Osteoblasts  Bone-forming cells  Osteoclasts  Bone-destroying cells  Break down bone matrix for remodeling and release of calcium  Bone remodeling is a process by both osteoblasts and osteoclasts

 AKA - Ossification  Bones are remodeled and lengthened until growth stops  Begins with the formation of other connective tissues  Provides the basis for bone shape  Collagen is the integral protein to provide framework for shape of bone. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 5.13b Bone Growth - Ossification  Intramembranous • Endochondral  Forms the skull and some • Forms the long bones, short facial bones bones, and some irregular bones  Forms from mesenchyme, • Forms from cartilage not cartilage • Primary ossification – fetal st  1 – Development of • Secondary ossification – after ossification “seed” birth  Calcification • Uses cartilage plates – Epiphyseal lines to produce  Forms spiny attachments – new bones using osteoblasts trabeculae • Cartilage is replaced by bone  Forms outer layer - periosteum from the “seed” to the periosteum For BOTH types of growth • New bone is deposited by osteoBLASTS

Figure 5.4a

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 5.14a Interstitial Growth • Growth attributed to maturation/growing up • Controlled by Hormones – Growth hormones – Metabolic hormones – thyroid hormones – Sex hormones • End when puberty completes Bone Remodeling • Why do bones remodel? – Nutrition – Disease – Exercise • Controlled by hormones – PTH – activates osteoclasts to remove calcium from the bones and return to circulation as an ion. – Calcitonin – activates osteoblasts to remove calcium from the blood and place it in the bones for storage. HIGH BLOOD CALCIUM

LOW BLOOD CALCIUM Bone Fractures

 A break in a bone  Types of bone fractures  Closed (simple) fracture – break that does not penetrate the skin  Open (compound) fracture – broken bone penetrates through the skin  Bone fractures are treated by reduction and immobilization  Realignment of the bone

Table 5.2

 Hematoma (blood-filled swelling) is formed  Break is splinted by fibrocartilage to form a callus  Fibrocartilage callus is replaced by a bony callus  Bony callus is remodeled to form a permanent patch

Figure 5.5