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Bone Tissue

Cartilage

  • Axial Skeleton: Includes bones of the skull, vertebral column, and rib cage.

  • Appendicular Skeleton: Includes bones of the limbs and their girdles.

  • Cartilages: Connective tissues providing support and flexibility.

    • Hyaline Cartilage CT: Found in locations such as the trachea, nose, and articulating surfaces of bones.

    • Elastic Cartilage CT: Found in the epiglottis and ear.

    • Fibrocartilage CT: Found in the intervertebral discs, pubic symphysis, and menisci.

Bone Classification

  • Long Bones: Examples include the humerus.

  • Short Bones: Examples include the talus.

  • Irregular Bones: Examples include the vertebrae.

  • Flat Bones: Examples include the sternum.

Functions of Bones

  1. Protection: Protects the brain, spinal cord, and vital organs.

  2. Support: Provides support for body shape.

  3. Movement: Bones act as levers for muscles to pull on, creating movement.

  4. Storage: Stores minerals such as calcium and phosphorus.

  5. Hematopoiesis: A place for blood cell formation in marrow cavities.

  6. Triglyceride (Fat) Storage: Occurs in bone cavities.

Long Bones

  • Compact Osseous CT: Located on the outside of the bone.

  • Spongy Osseous CT: Located on the inside at the ends of long bones.

Flat Bones

  • Compact Osseous CT: Located on the outer and inner surfaces.

  • Spongy Osseous CT (Diploe): Located on the inside between the compact bone layers.

Bone Structure

  • Proximal Epiphysis: The end of the bone closest to the trunk.

  • Epiphyseal Line: Remnant of the epiphyseal plate (growth plate).

  • Articular Cartilage: Covers the surfaces of bones where they come together to form joints.

  • Periosteum: Outer covering of the bone.

  • Spongy Bone: Contains trabeculae.

  • Compact Bone: Dense outer layer of bone.

  • Medullary Cavity: Lined by the endosteum, contains bone marrow.

  • Diaphysis: The shaft of the long bone.

  • Distal Epiphysis: The end of the bone farthest from the trunk.

  • Yellow Bone Marrow: Found in the medullary cavity.

  • Endosteum: Lines the inner surfaces of bone.

  • Nutrient Arteries: Supply blood to the bone.

  • Collagen Fibers: Connect periosteum to the bone tissue.

Hematopoietic Tissue

  • Newborns: Erythrocytes are made in red marrow in all marrow cavities of long and flat bones.

  • Adults: Erythrocytes are made in red marrow of the heads of the femur and humerus, and marrow cavities of flat bones.

  • All other adult marrow is yellow.

Periosteum

  • Peri-osteum: Bone covering.

  • Outer Fibrous Layer:

    • Dense irregular CT with collagen fibers.

    • Collagen in muscle tendons merges with these fibers.

  • Inner Osteogenic Layer: Contains bone cells.

    • Osteogenic cells: Stem cells that divide to become osteoblasts.

    • Osteoblasts: Bone-forming cells that make collagen.

    • Osteoclasts: Bone-destroying cells that remodel bone.

Endosteum

  • End-osteum: Bone linings.

  • Made of delicate reticular CT.

  • Lines the hollow part of the bone shaft.

  • Contains:

    • Osteogenic cells: Stem cells that divide to become osteoblasts.

    • Osteoblasts: Bone-forming cells that make collagen.

    • Osteoclasts: Bone-destroying cells that remodel bone.

Bone Cells

  • Osteogenic Cells: Divide and their daughter cells become Osteoblasts.

  • Osteoblasts: Produce collagen, to which calcium will attach.

  • Osteocytes: Mature bone cells that maintain the calcium balance in a bone by bringing it in from the blood.

  • Osteoclasts: Giant cells that digest bone with mild acids and enzymes during bone remodeling. Related to white blood cells.

Compact Osseous Tissue Structure

  • Endosteum: Lines bony canals and covers trabeculae.

  • Perforating Fibers

  • Lamellae

  • Nerve, Vein, Artery

  • Compact Osseous CT

  • Spongy Osseous CT

  • Blood vessels and nerves are found in the central canal.

  • Lamellae are layers in osteons

  • Collagen fibers within lamellae run in different directions to withstand twisting forces.

  • Osteocytes are connected by canaliculi, which allow nutrients to reach cells far from the blood supply in the central canal, and waste to be removed.

Spongy Osseous Tissue

  • Most cells are close enough to blood vessels in bone marrow to receive nutrition without osteons and canaliculi.

Bone Composition

  • Strong and Flexible = Concrete: Powered minerals (calcium phosphate) + water + flexible rebar (collagen).

  • Bones need to be strong and flexible.
    *Initially, bone forms as soft “osteoid.”

  • Osteoblasts secrete collagen into the space around the cell.

  • Osteoblasts secrete proteoglycan gel.

  • Then, inorganic salts arrive; calcium ions arrive in the blood.

  • Bone matrix starts to harden as phosphate ions arrive in the blood.

  • Hydroxyapatite forms, and the matrix hardens into bone.