The Skeletal System Bone as a Living Tissue

Functions of Bones 1. Support 1. Support 2. Protection 2. Protection 3. Movement 3. Movement 4. Storage 4. Storage (Minerals, medullary cavity stores marrow) (Minerals, medullary cavity stores marrow) 5. Blood cell formation 5. Blood cell formation Hematopoiesis Hematopoiesis

Bone Composition Cortical bone – dense outer layer; looks smooth & solid Cortical bone – dense outer layer; looks smooth & solid Trabecular (Spongy) bone – inner framework of small needle-like/flat pieces of bone (trabeculae) that have spaces in between Trabecular (Spongy) bone – inner framework of small needle-like/flat pieces of bone (trabeculae) that have spaces in between Spaces between filled with red or Spaces between filled with red or yellow bone marrow

Spongy Bone

Shape Categories of Bones 1. Long bones 1. Long bones All limb bones (except kneecap, wrist, & ankle bones) are long bones All limb bones (except kneecap, wrist, & ankle bones) are long bones

Long Bone Structure 1. Diaphysis – shaft of bone; cortical bone and medullary cavity with yellow bone marrow (fat) 1. Diaphysis – shaft of bone; cortical bone and medullary cavity with yellow bone marrow (fat) 2. Epiphyses – bone ends; covered in layer of articular cartilage, red bone marrow 2. Epiphyses – bone ends; covered in layer of articular cartilage, red bone marrow 3. Membranes – 3. Membranes – a. periosteum – double-layered membrane that covers external surface of bone a. periosteum – double-layered membrane that covers external surface of bone b. endosteum – lines medullary cavity b. endosteum – lines medullary cavity

Shape Categories of Bones 2. Short bones – cube shaped 2. Short bones – cube shaped Wrist and ankle bones Wrist and ankle bones 3. Flat bones – thin, somewhat curved 3. Flat bones – thin, somewhat curved Ribs, scapula Ribs, scapula

Shape Categories of Bones 4. Irregular bones – have complicated shape that does not fit in other 3 categories 4. Irregular bones – have complicated shape that does not fit in other 3 categories Vertebrae, hip bones are irregular Vertebrae, hip bones are irregular

Short Bone

Composition of Bone Osteocyte= mature bone cell Osteocyte= mature bone cell Osteon (aka Haversian system) – column parallel to long axis of bone Osteon (aka Haversian system) – column parallel to long axis of bone Haversian canal – run length of bone; osteocytes here Haversian canal – run length of bone; osteocytes here Lamella – hollow tubes of bone matrix; make up osteons; like rings on tree trunk Lamella – hollow tubes of bone matrix; make up osteons; like rings on tree trunk

Microscopic Anatomy of Compact Bone Lacunae – small cavities in bones Lacunae – small cavities in bones Volkmann’s canal – perforating canal; runs sideways, connects blood/nerve to central canals Volkmann’s canal – perforating canal; runs sideways, connects blood/nerve to central canals Canaliculi – small sideways canals connecting lacunae and central canal; tie all osteocytes in an osteon Canaliculi – small sideways canals connecting lacunae and central canal; tie all osteocytes in an osteon

Osteon

Bone Growth & Development Bone deposition, build bone – osteoblasts Remove/remodel – osteoclast Epiphyseal plate = growth plate

Ossification – Bone Development Aka osteogenesis Aka osteogenesis 1. Formation of bony skeleton 1. Formation of bony skeleton 2. Bone growth 2. Bone growth length length width (with stress) width (with stress) Hypertrophy vs. atrophy Hypertrophy vs. atrophy 3. Remodeling 3. Remodeling

Ossification

Factors Affecting Bone Development, Growth & Repair Deficiency of Vitamins: Vitamin A - slows bone development, Vita C – fragile bones, Vita D – rickets Insufficient or Excessive GH: dwarfism or Gigantism Sex Hormones – promote bone formation; stimulate ossification of epiphyseal plates Physical Stress – stimulates bone growth

Axial Skeleton