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.