1 Introduction Human skeleton initially cartilages and fibrous membranes Hyaline cartilage is the most abundant cartilage By age 25 the skeleton is completely hardened 206 bones make up the adult skeleton (20% of body mass) 80 bones of the axial skeleton 126 bones of the appendicular skeleton

2 Bone Classification Bone Classification: Long Bones Short Bones Sesamoid Bones Flat Bones Irregular Bones Wormian Bones (sutural) (a)(e) (b) (c) (d) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Classification of Bones Slide 5.4a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Long bones  Typically longer than wide  Have a shaft with heads at both ends  Contain mostly compact bone Examples: Femur, humerus

Classification of Bones Slide 5.4b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Short bones  Generally cube-shape  Contain mostly spongy bone  Examples: Carpals, tarsals

Classification of Bones on the Basis of Shape Slide 5.4c Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 5.1

Classification of Bones Slide 5.5a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Flat bones  Thin and flattened  Usually curved  Thin layers of compact bone around a layer of spongy bone  Examples: Skull, ribs, sternum

Classification of Bones Slide 5.5b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Irregular bones  Irregular shape  Do not fit into other bone classification categories  Example: Vertebrae and hip

Classification of Bones on the Basis of Shape Slide 5.5c Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 5.1

9 Parts of a Long Bone Epiphysis Distal Proximal Diaphysis Metaphysis Compact bone Spongy bone Articular cartilage Periosteum Endosteum Medullary cavity Trabeculae Bone marrow Red marrow and yellow marrow Femur Periosteum Yellow marrow Medullary cavity Space containing red marrow Spongy bone Compact bone Articular cartilage Epiphyseal plates Proximal epiphysis Distal epiphysis Diaphysis Endosteum Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

10 Microscopic Structure Bone cells are called osteocytes in a lacuna Osteocytes transport nutrients and wastes by cellular processes in canaliculi The extracellular matrix of bone is largely collagen and inorganic salts Collagen gives bone resilience & strength Inorganic salts make bone hard

11 Compact Bone Osteon aka Haversian System Central canal Perforating canal aka Volkmann’s canal Osteocytes Lamellae Lacunae Bone matrix Canaliculi Nerve Osteon Nerve Canaliculus Osteocyte Periosteum Endosteum Trabeculae Pores Bone matrix Blood vessels Spongy bone Compact bone Compact bone Lacuna (space) Blood vessels Perforating canal Central canal containing blood vessels and nerves Central canal Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Microscopic Anatomy of Bone Slide 5.10b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 5.3

Microscopic Anatomy of Bone Slide 5.11a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Lacunae  Cavities containing bone cells (osteocytes)  Arranged in concentric rings  Lamellae  Rings around the central canal  Sites of lacunae Figure 5.3

Microscopic Anatomy of Bone Slide 5.11b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Canaliculi  Tiny canals  Radiate from the central canal to lacunae  Form a transport system Figure 5.3

15 Spongy Bone Spongy bone is aka cancellous bone (a) (c) Spongy boneCompact bone (b) Spongy bone Compact bone Remnant of epiphyseal plate Spongy bone Compact bone Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. a: © Ed Reschke; b,c: Courtesy of John W. Hole, Jr.

16 Bone Development and Growth Parts of the skeletal system begin to develop during the first few weeks of prenatal development Bones replace existing connective tissue in one of two ways: As intramembranous bones As endchondral bones

17 Intramembranous Bones These bones originate within sheetlike layers of connective tissues They are the broad, flat bones Skull bones (except mandible) Are known as intramembranous bones

18 Endochondral Bones Bones begin as hyaline cartilage Form models for future bones These are most bones of the skeleton Are known as endochondral bones

19 Endochondral Ossification Hyaline cartilage model Primary ossification center Secondary ossification centers Epiphyseal plate Osteoblasts vs. osteoclasts (b)(c)(d)(e)(f)(a) Cartilaginous model Calcified cartilage Articular cartilage Developing periosteum Compact bone developing Primary ossification center Medullary cavity Medullary cavity Medullary cavity Secondary ossification center Secondary ossification center Blood vessel Epiphyseal plate Remnant of epiphyseal plate Remnants of epiphyseal plates Epiphyseal plates Compact bone Spongy bone Articular cartilage Spongy bone Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

20 Growth at the Epiphyseal Plate First layer of cells Closest to the end of epiphysis Resting cells Anchors epiphyseal plate to epiphysis Zone of resting cartilage Second layer of cells Many rows of young cells Undergoing mitosis zone of proliferating cartilage (a)(b) Bone tissue of epiphysis Zone of resting cartilage Zone of proliferating cartilage Zone of hypertrophic cartilage Zone of calcified cartilage Ossified bone of diaphysis Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. b: © The McGraw-Hill Companies, Inc./Al Telser, photographer

21 Growth at the Epiphyseal Plate Third layer of cells Older cells Left behind when new cells appear Cells enlarging and becoming calcified zone of hypertrophic cartilage Fourth layer of cells Thin Dead cells Calcified extracellular matrix zone of calcified cartilage (a)(b) Bone tissue of epiphysis Zone of resting cartilage Zone of proliferating cartilage Zone of hypertrophic cartilage Zone of calcified cartilage Ossified bone of diaphysis Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. b: © The McGraw-Hill Companies, Inc./Al Telser, photographer

22 Homeostasis of Bone Tissue Bone Resorption – action of osteoclasts and parathyroid hormone aka parathormone aka PTH Bone Deposition – action of osteoblasts and calcitonin Occurs by direction of the thyroid and parathyroid glands Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. © Biophoto Associates/Photo Researchers, Inc. Developing medullary cavity Osteoclast

23 Factors Affecting Bone Development, Growth and Repair Deficiency of Vitamin A – retards bone development Deficiency of Vitamin C – results in fragile bones Deficiency of Vitamin D – rickets, osteomalacia Insufficient Growth Hormone – dwarfism Excessive Growth Hormone – gigantism, acromegaly Insufficient Thyroid Hormone – delays bone growth Sex Hormones – promote bone formation; stimulate ossification of epiphyseal plates Physical Stress – stimulates bone growth

24 Bone Function Bones shape, support, and protect body structures

25 Support, Protection, and Movement Support, Movement & Protection Gives shape to head, etc. Supports body’s weight Protects lungs, etc. Bones and muscles interact When limbs or body parts move

26 Blood Cell Formation Also known as hematopoiesis Occurs in the red bone marrow

27 Inorganic Salt Storage Calcium Phosphate Magnesium Sodium Potassium