Overview of the Skeletal System

Skeletal System Overview

• The skeletal system is composed of bones, cartilage, ligaments, and tendons, working together to provide support, protection, movement, mineral storage, and blood cell production.
• Each bone is an organ, made of bone tissue, cartilage, dense connective tissue, epithelium, adipose tissue, and nervous tissue. Bone remodeling is a continuous process involving the building of new bone and the breakdown of old bone.
• Osteology is the study of bone structure and bone disorders.

Functions of the Skeletal System

• Support: Provides a framework for soft tissues and attachment points for muscles.
• Protection: Shields internal organs like the brain (cranium) and heart/lungs (rib cage).
• Movement: Skeletal muscles attach to bones, generating movement when they contract.
• Mineral Homeostasis: Stores and releases minerals like calcium and phosphorus, crucial for maintaining homeostasis and distributing these minerals throughout the body. Bone tissue stores ~99% of the body's calcium.
• Blood Cell Production: Red bone marrow within certain bones creates red blood cells, white blood cells, and platelets (hemopoiesis).
• Triglyceride Storage: Yellow bone marrow stores triglycerides as a potential energy source.

Macroscopic Bone Structure

• Diaphysis: The long, cylindrical shaft of a long bone.
• Epiphyses: The proximal and distal ends of a long bone.
• Metaphyses: The regions between the diaphysis and epiphyses (often containing growth plates).
• Articular Cartilage: A thin layer of hyaline cartilage covering the epiphyses reducing friction and absorbing shocks.
• Periosteum: A tough connective tissue sheath covering the bone surface, assisting in fracture repair, nourishing bone tissue, and providing attachment points for ligaments and tendons.
• Medullary Cavity: A hollow cylindrical space within the diaphysis containing fatty yellow bone marrow and blood vessels minimizing bone weight.
• Endosteum: A thin membrane lining the medullary cavity.

Bone Tissue Histology

• Bone tissue is ~15% water, ~30% collagen fibers, and ~55% crystallized mineral salts.
• The main mineral salt is calcium phosphate (Ca3(PO4)2), which combines with calcium hydroxide (Ca(OH)2) to form hydroxyapatite crystals (Ca10(PO4)6(OH)2).
• Calcification occurs as mineral salts are deposited in the collagen framework, hardening the tissue, and initiated by osteoblasts.

Bone Cells

• Osteoprogenitor Cells: Unspecialized bone stem cells derived from mesenchyme, the only bone cell that divides.
• Osteoblasts: Bone-building cells that synthesize and secrete collagen and other organic components to form bone tissue.
• Osteocytes: Mature bone cells, the main cells in bone tissue, maintaining daily metabolism.
• Osteoclasts: Large cells derived from monocytes that break down bone tissue (bone resorption).

Bone Tissue Types

• Compact Bone: Strongest bone type, with few spaces. Forms the outermost layer of all bones, and much of the diaphysis of long bones.
• Spongy Bone (Trabecular/Cancellous): Contains many open spaces and is found in the interior of bones, filled with bone marrow.

Bone Formation

• Intramembranous Ossification: Formation of bones directly from mesenchymal tissue.
• Endochondral Ossification: Formation of most bones by replacing hyaline cartilage models.

Factors Affecting Bone Growth & Remodeling

• Various hormones (Insulin-like growth factors, thyroid hormones, sex hormones) and minerals (Mg, P, Mn) influence bone growth and remodeling.

Clinical Connections

• Flatfoot: Reduced height of the medial longitudinal arch due to weakened supporting tissues.
• Bone fractures and structural abnormalities.

Appendicular Skeleton

• The appendicular skeleton includes the pectoral (shoulder) and pelvic girdles, as well as upper and lower limbs.

Axial Skeleton

• The axial skeleton includes the skull (cranial and facial bones), vertebral column, and hyoid bone.

This quiz explores the skeletal system's components, functions, and the study of osteology. It covers how bones provide support, protection, and facilitate movement. Additionally, it discusses the role of bones in mineral storage and blood cell production.