Overview
This lecture explains the structure, composition, and types of bones in the human skeleton, including their classification, function, and cellular makeup.
Skeletal Cartilage Overview
- Cartilage is a connective tissue with a high water content, providing flexibility and resilience.
- Chondrocytes are cartilage cells located in cavities called lacunae within an extracellular matrix.
- Three types of cartilage: hyaline (most common, supports ribs, nose, larynx, bone ends), elastic (ears, epiglottis), and fibrocartilage (spine, high pressure areas).
Bone Classification and Functions
- Bones are grouped into axial (head, torso) and appendicular (limbs, shoulders, pelvis) skeletons.
- Four bone shapes: long (limbs), short (wrists, ankles), flat (sternum, shoulder blades), and irregular (vertebrae, hips).
- Main bone functions: support, protection, movement (levers), mineral and fat storage, hormone production, and blood cell formation.
Bone Structure and Anatomy
- Bone is both a tissue and an organ, containing bone tissue, nervous tissue, blood vessels, and cartilage.
- Compact bone forms the dense outer layer; spongy bone is the porous internal structure filled with marrow.
- Short, flat, and irregular bones: spongy bone plates covered by compact bone, no distinct marrow cavity.
- Long bones: diaphysis (shaft, compact bone around marrow cavity), epiphyses (ends, spongy bone), covered by cartilage at joints.
- Yellow marrow stores fat; red marrow produces blood cells.
- Periosteum (outer membrane) has fibrous and osteogenic layers; connected to nerves and blood vessels.
- Endosteum covers inner surfaces of bone.
- Bone markings include projections, depressions, and openings for attachment and passage.
Microscopic Bone Anatomy & Cells
- Five key bone cell types: osteogenic cells (stem cells), osteoblasts (matrix-secreting, bone growth), osteocytes (mature, maintain matrix), bone lining cells (surface maintenance), and osteoclasts (breakdown bone, mineral release).
- Compact bone contains osteons (cylindrical structures of lamellae), giving strength and resisting twisting.
- Central canals within osteons house nerves and blood vessels; canaliculi connect lacunae and osteocytes.
- Lamellae: concentric (within osteons), interstitial (between osteons), circumferential (around diaphysis).
Chemical Composition of Bone
- Organic components: bone cells and osteoid (collagen, ground substance) for strength and flexibility.
- Inorganic components: hydroxyapatite (calcium phosphate crystals) for hardness and durability.
- The combination of organic and inorganic elements allows bones to resist tension and compression.
Key Terms & Definitions
- Chondrocyte — cartilage cell within a lacuna.
- Osteon — cylindrical unit in compact bone containing concentric lamellae.
- Diaphysis — shaft of a long bone.
- Epiphysis — end of a long bone.
- Periosteum — outer bone membrane with fibrous and osteogenic layers.
- Osteoblast — cell that builds bone by secreting matrix.
- Osteoclast — cell that breaks down bone for mineral release.
- Osteoid — organic part of bone matrix (mainly collagen).
- Hydroxyapatite — inorganic mineral component of bone (calcium phosphate).
- Lacuna — small cavity containing a bone cell or chondrocyte.
- Canaliculi — tiny channels connecting lacunae in bone.
Action Items / Next Steps
- Review the types and locations of cartilage in the skeleton.
- Memorize the four bone shapes and their examples.
- Study the five types of bone cells and their functions.