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Anatomy & Physiology Chapter 7: Skeletal System

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1 Anatomy & Physiology Chapter 7: Skeletal System

2 Introduction to Skeletal System
Human skeleton is initially cartilage and fibrous membranes 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 The organs of the skeletal system include the bones and structures that connect bones to other structures including ligaments, tendons, and cartilages.

3 Bone Classification Bone Classification: Long bones ex. femur
Short bones ex. tarsals Flat bones ex. skull Irregular bones ex. vertebrae Sesamoid bones ex. patella (b) (c) (d) (a) (e)

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

5 Parts of a Long Bone Diaphysis = shaft a. consists of central medullary cavity b. surrounded by a thick collar of compact bone Epiphyses = expanded ends a. consist mainly of spongy bone b. surrounded by a thin layer of compact bone c. proximal epiphysis vs. distal epiphysis Epiphyseal line = remnant of epiphyseal disc/plate a. cartilage at the junction of the diaphysis and epiphyses (growth plate)

6 Parts of a Long Bone Periosteum = outer protective covering of diaphysis a. supplied w/ blood, lymph vessels & nerves (nutrition) b. osteogenic layer contains osteoblasts (bone-forming cells) and osteoclasts (bone-destroying cells) c. serves as insertion for tendons and ligaments Endosteum = inner lining of medullary cavity a. contains layer of osteoblasts/osteoclasts Articular cartilage = pad of hyaline cartilage on the epiphyses where long bones articulate or join a. “shock absorber”

7 Parts of a Flat Bone Flat bones
1. covered by periosteum – covered compact bone 2. surrounding endosteum – covered spongy bone 3. In a flat bone the arrangement looks like a sandwich: a. spongy bone (meat) sandwiched between b. two layers of compact bone (bread) Hematopoetic tissue (red marrow) is located in the spongy bone within the epiphyses of long bones and flat bones

8 Microscopic Structure: Chemical Composition of Bone
Organic components (approx. 35%) Cells: osteoprogenitor cells 1. can undergo mitosis and become osteoblasts osteoblasts 1. form bone matrix by secreting collagen 2. cannot undergo mitosis osteocytes 1. mature bone cells derived from osteoblasts 2. principle bone cell 3. cannot undergo mitosis 4. maintain daily cellular activities (ie. exchange of nutrients & wastes with blood)

9 Microscopic Structure: Chemical Composition of Bone
Organic components…cont. Cells: Osteoid 1. primarily collagen (90% of bone protein) which gives bone its high tensile strength 2. other bone proteins include osteocalcin, osteonectin, and osteopontin 3. also contains glycolipids and glycoproteins Inorganic components Hydroxyapatite (mineral salts) which is primarily a. calcium phosphate [Ca3(PO4)2(OH)2] b. gives bone its hardness or rigidity

10 Microscopic Structure: Compact Bone
Compact bone is solid, dense, and smooth Structural unit = Haversian system or osteon a. elongated cylinders cemented together to form the long axis of a bone b. components of Haversian system osteocytes (spider shaped bone cells in “lacunaea” that have laid down a… matrix of collagen and calcium salts in… concentric lamellae (layers) around a… central Haversian canal containing… blood vessels and nerves. CONTINUED NEXT SLIDE

11 Microscopic Structure: Compact Bone
c. Communicating canals with compact bone -canaliculi connect the lacunae of osteocytes -Perforating (Volkmann’s) canal connect the blood & nerve supply of adjacent Haversian systems together.

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

13 Microscopic Structure: Spongy Bone
Consists of poorly organized trabeculae ( small needle-like pieces of bone) with a lot of open space between them nourished by diffusion from nearby Haversian canals

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

15 Bone Development and Growth
Introduction The “skeleton” of an embryo is composed of fibrous CT membranes ( formed from mesenchyme and hyaline cart) that is loosely shaped like bone. This skeleton provides supporting structures for ossification to begin. At about 6-7 wks gestation ossification begins and continues throughout adulthood.

16 Bone Development and Growth
Ossification follows one of two patterns Intermembranous Ossification When bone forms on or within a fibrous CT membrane ex. Flat bones are formed in this manner Endochondral ossification Occurs when a bone is formed from a hyaline cartilage model. a. most bones of the skeleton are formed this way b. Primary ossification center hardens as fetus or infant c. Secondary ossification centers develop in child and harden during adolescence and early adulthood During infancy and childhood long bones lengthen entirely by growth at the epiphyseal plates (longitudinal growth) Bones grow thicker by “appositional growth”

17 Endochondral Ossification
Hyaline cartilage model Primary ossification center Secondary ossification centers Epiphyseal plate Osteoblasts vs. osteoclasts Articular cartilage Remnants of epiphyseal plates Secondary ossification center Cartilaginous model Developing periosteum Compact bone developing Spongy bone Epiphyseal plates Blood vessel Medullary cavity Medullary cavity Medullary cavity Compact bone Remnant of epiphyseal plate Epiphyseal plate Calcified cartilage Primary ossification center Secondary ossification center Spongy bone Articular cartilage (a) (b) (c) (d) (e) (f)

18 Growth at the Epiphyseal Plate
The epiphyseal plate allows for bone lengthening until adulthood. As a child grows… a. cartilage cells are produced by mitosis on the epiphyseal side of the plate b. they are then destroyed and replaced by bone on the diaphyseal side of the plate *therefore the thickness of the plate remains almost constant while the bone on the diaphyseal side increases in length. c. the cartilage of the epiphyseal plate is replaced by bone forming the epiphyseal line. d. ossification of most bones is completed by age 25.

19 Bone Thickening: Appositional Growth
Along with increasing in length bones increase in thickness or dia. 1. occurs in osteogenic layer of periosteum 2. Osteoblasts lay down matrix (compact bone) on outer surface 3. This is accompanied by osteoclasts destroying the bone matrix at the endosteal surface.

20 Homeostasis of Bone Tissue
Once bones are formed, the actions of osteoclasts and osteoblasts continually remodel them Bone remodeling occurs throughout life a. osteoclasts resorb bone b. osteoblasts replace the bone c. these opposing processes are highly regulated so that total mass of bone tissue in adult skeleton normally remains constant even though 3-5% of bone calcium is exchanged each year.

21 Homeostasis of Bone Tissue
Bone Resorption – action of osteoclasts via stimulation from parathyroid hormone (PTH) Bone Deposition – action of osteoblasts and via stimulation from calcitonin Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Developing medullary cavity Osteoclast © Biophoto Associates/Photo Researchers, Inc.

22 Bone Function Support Bones in legs and pelvis support trunk
The atlas (1st vertebra) supports the skull etc Protection of underlying organs The skull protects the brain The rib cage protects the heart and lungs etc. Body Movement a. Skeletal muscles attached to bones by tendons b. Serve as levers to move bones. Hematopoiesis Blood cell formation a. All blood cells formed in the red marrow of certain bones

23 Divisions of the Skeleton
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Axial Skeleton Skull Spine Rib cage Cranium Skull Face Hyoid Clavicle Scapula Sternum Humerus Ribs Vertebral column Vertebral column Appendicular Skeleton Upper limbs Lower limbs Shoulder girdle Pelvic girdle Hip bone Carpals Sacrum Radius Coccyx Ulna Metacarpals Femur Phalanges Patella T ibia Fibula T arsals Metatarsals Phalanges (a) (b)

24 7.6: Skull Is composed of the cranium (brain case) and the facial bones

25 7.7: Vertebral Column The vertebral column, or spinal column, consists of many vertebrae separated by cartilaginous intervertebral discs.


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