Functions of the Skeletal System

Functions of the Skeletal System

• Provides a framework supporting the body and cradling soft organs.
• Encases vital organs, protecting them (e.g., skull protects the brain, rib cage protects the heart and lungs).
• Acts as levers for muscles, enabling movement via muscle contraction and relaxation.
• Stores minerals (e.g., calcium, phosphorus) and lipids in yellow bone marrow.
• Produces blood cells in red bone marrow.

Definition of a Sesamoid Bone

• Small, round bone embedded within a tendon or muscle, often where the tendon crosses a joint.
• The patella (kneecap) is a common example.

Structures of a Typical Long Bone

• Articular Cartilage: Hyaline cartilage covering bone ends at joints, reducing friction and absorbing shock.
• Diaphysis: Long, cylindrical shaft of the bone, primarily compact bone.
• Endosteum: Thin membrane lining the medullary canal and internal bone surfaces.
• Epiphyseal Line: The remnant of the epiphyseal plate in adults, signifying former growth areas.
• Epiphyseal Plate: Hyaline cartilage layer for bone growth in children and adolescents.
• Epiphysis: The ends of a long bone, consisting of spongy bone coated with compact bone.
• Foramen: Opening in a bone for nerves and blood vessels.
• Medullary Canal: Central cavity of the diaphysis, housing yellow bone marrow.
• Periosteum: Dense, vascular connective tissue coating bones for tendon and ligament attachment.
• Red Bone Marrow: Site of hematopoiesis (blood cell formation), found in certain bones.
• Yellow Bone Marrow: Mostly adipose tissue, serving as an energy reserve.

Types of Connective Tissue in the Skeletal System

• Bone Tissue: Hard, dense connective tissue forming the skeleton, providing structure and support.
• Cartilage: Flexible connective tissue providing support, cushioning joints, and facilitating growth.

Compact Bone vs. Spongy (Cancellous) Bone

• Compact Bone: Dense outer layer for strength and support, organized into osteons.
• Spongy Bone: Lighter, porous bone at ends of long bones and interior of some bones, containing trabeculae and red bone marrow.

Microscopic Structure of Bone

• Osteon (Haversian System): Fundamental functional unit of compact bone, concentric lamellae surrounding a central canal.
• Lamella: Thin layers of bone matrix forming the osteon.
• Central Canal (Haversian Canal): Contains blood vessels and nerves, running through the center of each osteon.
• Lacunae: Small cavities in the bone matrix containing osteocytes.
• Canaliculi: Tiny channels connecting lacunae, facilitating nutrient and waste exchange between osteocytes.
• Osteocytes: Mature bone cells maintaining bone tissue and communicating via canaliculi.

Nature, Structure, and Function of Cartilage

• Nature: Flexible connective tissue for support and structure.
• Structure: Chondrocytes embedded in an extracellular matrix rich in collagen and elastic fibers.
• Function: Cushions joints, supports structures (like nose and ears), and allows for long bone growth.

Process of Bone Formation and Growth (Osteogenesis)

• Endochondral Ossification: Bone development by replacing hyaline cartilage, common in long bones.
• Role of Osteoblasts: Synthesize new bone matrix and promote mineralization.
• Role of Osteoclasts: Break down bone tissue, allowing for remodeling and growth.
• Epiphyseal Plate: Growing tissue near long bone ends where new bone forms.
• Epiphyseal Line: Remnant of the epiphyseal plate after growth ceases, signifying growth cessation.

Axial Skeleton vs. Appendicular Skeleton

• Axial Skeleton: Skull, vertebral column, rib cage, supporting the body's central axis.
• Appendicular Skeleton: Bones of limbs and girdles (pectoral and pelvic) attaching limbs to the axial skeleton.

Number of Bones in the Mature Human Skeleton

• 206 bones.