Histology and Physiology of Bones

Osteon

Structural unit of compact bone containing central canals.

Skeletal System Components

Includes bones, cartilage, tendons, and ligaments.

Functions of Bones

Support, protection, movement, storage, and blood cell production.

Chondroblasts

Cells that produce cartilage and become chondrocytes.

Lacunae

Small cavities in cartilage housing chondrocytes.

Bone Matrix Composition

35% organic, 65% inorganic materials.

Hydroxyapatite

Calcium phosphate crystal providing bone strength.

Osteoblasts

Cells that produce bone matrix and become osteocytes.

Osteocytes

Mature bone cells located in lacunae.

Osteoclasts

Cells responsible for bone resorption.

Ossification

Process of bone formation from cartilage.

Woven Bone

Immature bone with collagen fibers in various directions.

Lamellar Bone

Mature bone with parallel collagen fibers in layers.

Cancellous Bone

Bone with many spaces, filled with marrow.

Compact Bone

Dense bone with few spaces, organized structure.

Trabeculae

Lattice-like structures in cancellous bone providing strength.

Circumferential Lamellae

Outer layers of compact bone surrounding the surface.

Concentric Lamellae

Layers surrounding central canals in osteons.

Diaphysis

Tubular shaft of long bones containing medullary cavity.

Epiphysis

Expanded ends of long bones, containing spongy bone.

Epiphyseal Plate

Site of bone length growth in long bones.

Periosteum

Double-layered membrane covering outer bone surface.

Endosteum

Membrane covering internal surfaces of bone.

Articular Cartilage

Hyaline cartilage covering joint surfaces of bones.

Flat Bones

Contain cancellous bone between two compact layers.

Short Bones

Similar composition to ends of long bones.

Irregular Bones

Have a structure like short bones.

Intramembranous Ossification

Bone develops from a fibrous membrane.

Endochondral Ossification

Bone forms by replacing hyaline cartilage.

Fontanels

Unossified membrane areas in newborn skull.

Primary Ossification Center

Initial site where bone matrix is laid down.

Secondary Ossification Centers

Form in the epiphyses during bone development.

Appositional Growth

Increase in bone diameter by surface addition.

Zones of Epiphyseal Plate

Four zones: resting, proliferation, hypertrophy, calcification.

Articular Cartilage Growth

Interstitial growth followed by appositional bone growth.

Bone Remodeling

Process of renewing and reshaping bone.

Basic Multicellular Units (BMUs)

Temporary assemblies of osteoclasts and osteoblasts.

Bone Fractures

Classified by position, completeness, orientation, and skin penetration.

Hematoma Formation

Clotted blood mass forms at fracture site.

Callus Formation

Granulation tissue forms around fracture site.

Callus Ossification

Internal and external calluses ossify to form bone.

Calcium Homeostasis

Regulation of calcium levels in the blood.

Parathyroid Hormone (PTH)

Major regulator of blood calcium levels.

Calcitonin

Hormone that decreases blood calcium levels.

Effects of Aging

Bone matrix loss leads to brittleness and fractures.

Osteoporosis

Condition characterized by reduced bone density.