Bone Tissue

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Function of bones

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Support-structural framework
Protection-skull, vertebrae, rib-cage
Movement-attachment for muscles
Mineral homeostasis-calcium balance
Blood cell production-RBC & WBC red bone marrow
Fat storage-yellow bone marrow

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Types of bones

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Long bone (humerous), Flat bone (sternum, skull), irregular bone (vertebrae), sesamoid bone (patella, forms in a tendone when there is a lot of stress), short bone (carpal)

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Diaphysis

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the bone's shaft or body-the long, cylindrical main portion of the bone

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Epiphysis

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are the distal and proximal ends of the bone

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metaphyses

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are the regions in a mature bone where the diaphysis joins the epiphyses. in a growing bone each metaphysis includes a epiphyseal plate

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Epiphyseal plate

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a layer of hyaline cartilage that allows the diaphysis of the bone to grow in length.

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Epiphyseal line

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the boney structure that results when a bone stops groing in length and the carilage in the epiphyseal plate is replaced by bone

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articular cartilage

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a thin layer of hyaline cartilage covering the part of the epiphysis where the bone forms an articulation (joint) with another bone. reduces friction and absorbs shock

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periosteum

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a round tough sheath of dense irregular connective tissue that surounds the bone surface wherever it is not covered by articular cartilage. allows growth in width, protects bone, assists fracture repair, nourish bone tissue, an attachment point for ligaments and tendons. outer layer-connective tissue, inner layer-osteogenic cells and osteoblasts

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perforating fibers

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thick bundles of collagen fibers that extend from the periosteum into the extracellular bone matrix

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Medullary cavity

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the space w/in the diaphysis that contains fatty yellow bone marrow in adults

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endosteum

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a thin membrane that lines the medullary cavity. has single layer of bone-forming cells and a bit of connective tissue

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bone matrix

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25%water, 25%collagen, 50% salts. Collagen contributes to flexibility. Salts-calcium phosphate & calcium hydroxide combine to form crystals of hydroxyaphite. calcium carbonate, magnesium, flouride, potassium, sulfate.

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calcification

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the process where mineral salts are deposited on the framework of fibers making bones hard...initiated by osteoblasts

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Osteogenic cells

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stem cells drived from mesenchyme...only bone cells undergoing mitosis, resulting cells develop into osteoblasts. found inner portion of periosteum, in the endosteum and the canals w/in bone that contain vessels

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osteoblasts

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bone building cells. no cell division, synthesize and secrete collagen fibers and other organic components necessary for extracellular matrix of bone tissue, initiate calcification. they get trapped in own secretions and become osteocytes.

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Osteocytes

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Maintain bone tissue...no cell division.

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Osteoclasts

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huge cells derived from many monocytes (type of WBC) and are concentrated in endosteum. brake down bone either to remodel or free up calcium

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Compact bone tissue

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contains few spaces, strongest form of bone tissue, beneath the periosteum of all bones, makes up the bul of the diaphyses of long bones. support and protection

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perforating canals

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blood vessels, lymphatic vessels, and nerves from the periosteum penetrate compact bone through these transverse canals

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central (haversian) canals

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run longitudinally through the bone, connect with the vessels and nerves of the perforating canals

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concentric lamellae

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rings of calcified extracellular matrix surrounding the central canals.

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lacunae

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small spaces between the lamellae which contain osteocytes.

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canaliculi

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tiny channels filled w/extracellular fluid that radiate in all directions from the lacunae. system of canaliculi provides many routes for nutrients and oxygen to reach osteocytes and for waste removal

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osteon

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or haversian systems, components of compact bone tissue are arranged into these repeating units. each osteon has a central canal with its rings of lamellae, lacunae, osteocytes and canaliculi. aligned in the same direction along lines of stress

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intersticial lamellae

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fragments of older osteons that have been partially destroyed during bone rebuilding or growth, between osteons look like triangles

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circumferential lamellae

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lamellae that encircle the bone just beneath the periosteum or encircle the medullary cavity. the outside circle

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spongy bone

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consists of lamellae arranged in an irregular lattice of thin columns called trabeculae; spaces between trabeculae of some bones are filled w/red bone marrow;found inside short, flat and irregular bones and in the epiphyses of long bones.

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Trabeculae

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with in each are lacunae that contain osteocytes and canaliculi radiate outward from the lacunae. osteocytes of spongy bone are located on the superficial surfaces of trabeculae they get nourishment directly from the blood circulating through the medullary cavities.

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Periosteal arteries

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along with nerves they enter the diaphysis through many perforating canalsand supply the periosteum and outer part of the compact bone

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nutrient artery

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passes through a hole in compact bone called the nutrient foramen.

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metaphyseal arteries

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enter the metaphyses of a long bone and together with the nutrient artery supply the red bone marrow and bone tissue of the metaphyses

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epiphyseal arteries

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enter the epiphyses of a long bone and supply the red bone marrow and bone tissue of the epiphyses

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nutrient veins

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carry away blood and accompany the nutrient artery in the diaphysis

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epiphyseal veins and metaphyseal veins

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exit their respective arteries in the epiphyses

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periosteal veins

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exit with their respective arteries in the periosteum

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ossification or osteogenesis

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process by which bone forms...happens in 2 ways

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intramembranous ossification

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flat bones form between 2 membranes...skull and lower jawbone formed this way

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endochondral ossification

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a cartilage model of the bone forms and bone tissue replaces the cartilage

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What happens during intramembranous ossification

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Mesenchyme cells cluster and become osteogenic cells. osteogenic cells develoop into osteoblasts, osteoblasts produce bone matrix. the osteoblasts become osteocytes that lie in lacuna. matrix hardens. Trabecula grow to form spongy bone. the periosteum develops on the surface and osteoblasts put down compact bone tissue.

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What happens in endochondral ossification?

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Mesenchyme cells become chondroblasts creating hyalin cartilage surrounded by the perichondrium. The cartilage model grows. Primary ossification center Chondrocytes begin calcification and grows into and up the diaphysis. The perichondrium begins to put down bone as well and becomes known as the periosteum. Blood vessels grow into model. Spongy bone continues to form. The medullary cavity forms by osteoclasts. Secondary centers of ossification in epiphysis develop and bone spreads through the epiphysis and the diaphysis Cartilage remains in the bone at the epiphyseal plate and articulating surfaces

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4 Zones of Epiphyseal plate

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Zone of resting cartilage-normal cartilage
Zone of proliferating cartilage-mitosis
Zone of hypertrophic cartilage-mature chondrocytes
Zone of calcified cartilage-bone formation. Because of the cell division in the epiphyseal plate, the diaphysis of a bone increases in length.

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Bone growth thickness

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Ridges in periosteum create a groove for periosteal blood vessel. Periosteal ridges fuse, forming an endosteum-lined tunnel. Osteoblasts in endosteum build new concentric lamellae inward toward center of tunnel, forming a new osteon. Bone grows outward as osteoblasts in periosteum build new circumferential lamellae. Osteon formation repeats as new periosteal ridges fold over blood vessels.

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Healing bone

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Fracture hematoma (blood clot) forms, bone cells die, swelling and inflammation occurs bringing in phagocytes and osteoclasts that come to clean up. Fibroblasts move in and produce collagen, chondroblasts develop forming a fibrocartilage callus which replaces the hematoma. Blood vessels begin to grow in, and fibrocartilage is converted into spongy bone. Osteoclasts and osteoblasts then remodel the bone into its original shape.

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Calcium homeostasis

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Parathyroid hormone (pth) secreted by the parathyroid gland increases blood calcium level, whereas calcitonin (CT) from the thyroid gland has the potential to decrease blood calcium level. EX. if blood calcium level is too low Parathyroid gland secretes PTH causing kidneys to retain calcium and stimulates osteoclasts which pull calcium from the bones and makes it available to blood.

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Osteoporosis

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condition of porous bones. Estrogen and testosterone stimulate osteoblasts