Chapter 7: Bone Tissue- 7.1 Tissue and Organs of the Skeletal Systemo Skeletal System: composed of bones, cartilage, and ligaments joined tightly to form a strong, flexible framework for the bodyo Functions of the Skeleton Support:- Limbs and vertebral column support body- Mandible and Maxilla support teeth Protection: - Brain, spinal cord, heart, lungs, pelvic viscera, and bone marrow Movement: - Limbs and breathing Electrolyte Balance: - Stores calcium and phosphate ions- Releases them as needed in the body  Acid-Base balance: - Buffers blood by absorbing or releasing alkaline phosphate and carbonate salts Blood Formation: - Red bone marrow produces blood cells and immune cellso Bones and Osseous Tissue:  Osseous Tissue: connective tissue in which the matrix is hardened by deposition of calcium phosphate and other minerals - Mineralization or Calcification: the hardening processo General Features of the Bone Flat Bones: thin curved plates like the parietal bones, sternum, scapula, ribs, and hip bones- Diploe: spongy layer in between two compact bone layers Long Bones: serve as rigid levers that are acted upon by skeletal muscles to produce major movements- Most important bones in the body for movement- Compact dense bone, medullary cavity, spongy bones- Diaphysis: the shafto Provides leverage- Epiphysis: an expanded head at each end of the shafto Strengthens the joint and provides added surface area for the attachment of tendons and ligaments- Articular cartilage: covers the joint surface where one bone meets another o Enables joint to move far more easily than it would ifone bone rubbed directly against the other- Nutrient Foramina: where blood vessels penetrate- Humerus, radius, ulna, femur, tibia, fibula, and metatarsals Short Bones: approximately equal in length and width and produce relatively limited gliding movements- Total of 30  Irregular Bones: bones that do not fit the above categories- Vertebrae and ear bones Compact Dense Bone: and outer shell of dense white osseous tissue that encloses a medullary cavity- Contains bone marrow Spongy Bone: usually at the end of bones that is a more loosely organized form of osseous tissue- Always enclosed by compact bone Periosteum: a sheath that covers the entire bone - Outer fibrous layer of collagen o Can be continuous with tendons or penetrate bone matrix (perforating fibers)- Inner osteogenic layero Important growth of bone and healing fractures  Endosteum: thin layer of reticular connective tissue that lines the internal marrow cavity, covers all the spongy bone, and lines canal systems Epiphyseal Plate: hyaline cartilage that separates the marrow spaces of the epiphysis and diaphysis- Also known as growth plate- Epiphyseal ‘line’: is found in adults- 7.2: Histology of Osseous Tissueo Bone Cells:  Osteogenic Cells: stem cells that develop from embryonic mesenchymal cells- Found in Endosteum and inner Periosteum - Become osteoblasts Osteoblasts: bone forming cells- Nonmitotic- Synthesize soft matter of the bone matrix- Secrete hormone Osteocalcino Stimulates insulin secretion by pancreas, increases insulin sensitivity in adipocytes, and limits the growth of adipose tissue Osteocytes: former osteoblasts that have become trapped in the matrix they have deposited - Reside in lacunaeo Interconnected by canaliculi- Connected by other osteocytes through gap junctionso Pass nutrients and chemical signals and pass metabolic wastes - Functions o Resorb bone matrix or deposit it  Homeostatic maintenance of bone density and blood concentrations of calcium and phosphate ionso Strain sensors  Adjustments in bone shape and density to adapt stress- Osteoclasts: bone-disssolving cells on the bone’s surfaceo Formed by fusion of several stem cells Unusually large Multinucleated  Reside in resorption bays (pits) o The Matrix: dry by weight, 1/3 organic, and 2/3 inorganic matter Organic matter: synthesized by osteoblasts  Inorganic Matter: 85% hydroxyapatite- Crystalized calcium phosphate salt  A composite: combination of two basic structural materials—ceramic (hydroxyapatite) and polymer (collagen)- Cermaic: enables bone to support the weight of body without sagging- Polymer: protein component gives bone a degree of flexibilityo Collagen molecules have sacrificial bones that break under stress o Compact Bone:  Concentric Lamellae: layers of matrix concentrically arranged around a central canal and connected with each other by canaliculi- Osteon: basic structural unit of compact bone  Perforating canals: transverse canals - Lined by Endosteum Collagen fibers corkscrewed creates strength of bone  Circumferential lamellae and interstitial lamellaeo Spongy Bone:  Spicules and Trabeculae: a lattice of delicate slivers of bone  Arranged in lamellae, but very few osteons Central canals are not needed  Designed to impart strength to bone while adding a minimum of weighto Bone Marrow: general term for soft tissue that occupies the marrow cavity of the long bone Red Bone Marrow (hemopoietic): produces blood cells- In adults this usually turns to yellow marrow Yellow Marrow: fat at center of a ham bone - No longer produces blood- 7.3 Bone Development: ossification/osteogenesiso Intramembranous Ossification: produces the flat bones of the skull and most of the clavicle  Mesenchyme first condenses into a soft sheet with blood vessels - Cells line up along blood vessels and become osteoblasts that secrete osteoid tissue (prebone) in the direction away from the blood vessel Minerals crystallize the collagen fibers of osteoid tissue and hardened matrix- This squeezes the blood vessels and future bone marrow into narrower spaces - Osteoblasts get stuck in their own matrix and become osteocytes More mesenchyme cells condense to form Periosteum on each surface - Spongy bone becomes a honeycomb  Osteoblasts beneath Periosteum deposit layers of bone, fill spaces between trabeculae, and create zone of compact bone on each side Plays role in life long thickening, strengthening, and remodeling of the long boneso Endochondral Ossification: a process in which a bone develops from a preexisting model composed of hyaline cartilage  Begins week 6 of fetal development and continues until 20s Mesenchyme develops into a body of hyaline cartilage covered with perichondrium - Cartilage model grows and thickens Primary ossification