Human Skeleton: The human skeleton consists of over 200 bones of different sizes and shapes that play a variety of roles in maintaining our health and well-being. Bones provide the basic structural framework for our muscles and allow us to stand upright and move about. Bones also encase and protect sensitive organs of the body such as the brain, heart, spinal cord and eyes from injury from external forces.

Skeletal Problems Disease / genetics Osteoporosis (Type I) Multiple myeloma Metastatic bone cancer Rheumatoid arthritis Paget’s Disease Hormone ablative therapy Spinal cord or nerve injury Surgery and rehabilitation Aging (Type II Osteoporosis) Bedrest Microgravity

Structural Support Protection Movement Mineral Storage Calcium Functions of Bone Structural Support Protection Movement Mineral Storage Calcium Phosphate

Bone structure and composition

Types of bone Two major types of bones 1. Compact (cortical, i. e Types of bone Two major types of bones 1. Compact (cortical, i.e., long bones) Mechanical and protective functions 2. Cancellous (spongy, i.e., vertebrae) Metabolic regulation of calcium

Bone composition 70% mineral (Ca2+ and PO4- as hydroxyapatitie) 22% protein (95% Type I collagen + 5% proteoglycans and other materials) 8% water Bone is a connective tissue that consists principally of a mineralized extracellular matrix plus the specialized cells, Osteoblasts Osteocytes Osteoclasts Bone lining cells

Osteoblasts and osteocytes Osteoblasts, the bone forming cells work in groups to secrete and then mineralize patches of new bone matrix. Characteristics of Osteoblasts Matrix formation Secretes Type I collagen Regulates mineralization Positioned above osteoid matrix Matrix usually polarized but can surround cells