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The Skeletal System Chapter 6, 7,& 8 Martini, 1st Ed. Anatomy and Physiology Liberty Senior High School Question of the Day! Do bones remain the same? How do bones “know” when to stop growing? What happens when they don’t? The Skeletal System! Our First System Cells (Osteocytes) Tissues (Osseous Tissue) Organs (Bones) Systems (Skeletal) All C.T. have Three Parts 1. Specialized Cells 2. Extracellular Protein Fibers 3. The Fibers above and a ground substance (usually a liquid)- make up the Matrix that surrounds cells. (most of the volume of C.T.) The Fibers • Collagen Fibers- long, straight, unbranched, fibers of twisted protein; rope-like, very flexible, yet strong. (Tendons and Ligaments) The Matrix • G.S. = almost no liquid; collagen fibers + calcium salts (CaPO4 and some CaCO3) • Strong and flexible properties. • Lacunae in matrix contain osteocytes. Bone (Osseous Tissue) • Lacunae organized around a central canal (Haversian canal) which contains blood vessels. • Diffusion cannot occur through calcium salts. • Cytoplasm of osteocytes extend to central canal by canaliculi. A Basic Pattern in Bone Tissue • Lacunae with osteocytes arranged around and connected to a central canal by radiating canaliculi- Osteon • Many osteons in one bone. Bone-Low Mag. Bone-High Mag. Osteons Haversian or Central Canal Two Types of Osseous Tissue 1. Compact bone- dense bone, solid, more on surface of bone, shaft of bone. Function: osteons are all alligned;strengthen bone, the tissue of bone is parallel to stresses. Two Types of Osseous Tissue 2. Spongy Bone- open network of trabeculae which are struts and plates in the interior of bone (matrix) , light in weight; Function: has no osteons; withstand stress from a variety of directions, reduce the weight of the overall bone. Bone (Osseous Tissue) • Bone surfaces covered by periosteum- fibrous layer of C.T.; attachment for tendons and ligaments. • Site of appositional growth of bone. • Bone is constantly remodeled- grow thicker with stresses. http://www.bio.psu.edu/f aculty/strauss/anatomy/s kel/skeletal.htm Bone Development & Growth Bony skeleton begins to form 6 weeks after fertilization (12 mm) Osteogenesis Ossification- formation of bone is a dynamic process. Osteoblasts- produce new bone matrix. Osteoclasts- produce acids and enzymes to release the stored minerals in the matrix. Osteocytes- mature bone cells that do not divide. Osteoblasts Osteoclasts Bone Cell Interaction 2 types of Ossification Intramembranous - bone develops from mesenchyme or fibrous C.T. Endochondral – bone replaces existing cartilage Intramembranous ossification Occurs in the deeper layers of the dermis- Dermal bones Ex: top of skull, mandible, clavicle, abnormal stressed areas like tendons, joints, skeletal muscles (heterotopic bones- different place) Intramembranous ossification 1.Formation of bone matrix w/in the fibrous membrane • Mesenchymal cells make the the matrix of calcium salts • Mesenchymal cells turn into osteoblasts • Ossification occurs: Osteoblasts Osteocytes Intramembranous ossification 2. Formation of bone •Bone grows outward in small struts called: Spicules (form trabeculae) •Blood vessels become trapped among spicules Intramembranous ossification 3. Formation of Compact Bone & periosteum •Small amount of spongy bone is replaced with mature compact bone • Mesenchyme makes periosteum Heterotopic Bone Formation FOP Endochondral Ossification 1. Hyaline chondrocytes die & disintegrate leaving cavities within cartilage. 2. Blood vessels grow at edges & perichondrial cells become osteoblasts (turns to bone on the edges). Endochondral Ossification 3. -Blood vessels penetrate the central region ( fibroblasts osteoblasts) -Bone development begins at Primary Center of Ossification (go towards ends) Endochondral Ossification 4. Osteoclasts- create a marrow cavity by dissolving struts Endochondral Ossification Increasing the Length • Osteoblasts of the diaphysis and chrondrocytes of epiphysis continue to grow; elongate bone. • Epiphyseal Plate is this interface between the two. Endochondral Ossification 5.-Center of epiphyses begin to calcify -Capillaries & osteoblasts migrate into this area. -Secondary Ossification Center Endochondral Ossification 6. Epiphysis is filled with spongy bone -Articular cartilage remains at exposed joint cavity -At the metaphysis, epiphyseal plate separates the epiphysis from the diaphysis Endochondral Ossification •At puberty, the osteoblasts overcome chondrocytes; the plate becomes more narrow- epiphyseal line. Bone Formation In An Embryo Growth Plate Endochondral Ossification Fetal Long Bone Developing Long Bone Increasing the Diameter •Enlarges through Appositional Growth at outer surface •Periosteal cells Osteoblasts Osteocytes •Osteoclasts remove bone matrix at inner surface Achondroplasia When bones don’t stop growing!
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