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Introduction to the Skeletal System Chapter 6 Lecture Notes

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Title: Introduction to the Skeletal System Chapter 6 Lecture Notes


1
Introduction to the Skeletal SystemChapter 6
Lecture Notes
  • to accompany
  • Anatomy and Physiology From Science to Life
  • textbook by
  • Gail Jenkins, Christopher Kemnitz, Gerard Tortora

2
Chapter Overview
  • 6.1 Skeletal System Functions
  • 6.2 Bone Classification
  • 6.3 Long Bones
  • 6.4 Osseous Tissue
  • 6.5 Blood Vessels and Nerves
  • 6.6 Bone Formation
  • 6.7 Bone Growth
  • 6.8 Bone Remodeling

3
Essential Terms
  • skeletal system
  • entire framework of bones and their cartilages
  • osseous tissue
  • bone tissue

4
Introduction
  • Skeletal system is made up of
  • bones
  • cartilages
  • each individual bone is considered an organ
  • complex and dynamic living tissues
  • continuously remodeled

5
Concept 6.1Skeletal System Functions
6
Skeletal System Functions
  • Support
  • structural framework for body
  • Protection
  • protects internal organs from injury
  • Movement
  • skeletal muscles pull on bones
  • Mineral Homeostasis
  • calcium and phosphorus stored and released
  • Blood Cell Production
  • red bone marrow produces blood cells
  • Energy Storage
  • triglycerides stored in yellow marrow

7
Concept 6.2 Classification of Bones
8
Bone Classification
  • Shape
  • long
  • short
  • flat
  • irregular
  • sesamoid

9
Figure 6.1
10
Bone Shape
  • long bones
  • greater length than width
  • shaft and two ends
  • short bones
  • somewhat cube-shaped
  • flat bones
  • generally thin
  • irregular bones
  • complex shapes
  • sesamoid bones
  • vary from person to person except patellae
  • develop in tendons and improve mechanical
    advantage of joint

11
Concept 6.3 Long Bones
12
Long Bone Anatomy
  • diaphysis
  • shaft
  • epiphyses
  • distal and proximal ends
  • metaphyses
  • region in mature bone where diaphysis meets
    epiphyses
  • includes epiphysial line
  • replaces epiphysial plate in growing bone
  • articular cartilages
  • hyaline cartilage covering epiphyses

13
Long Bone Anatomy
  • 5. periosteum
  • dense irregular connective tissue
  • surrounds external surface except epiphyses
  • contains bone-forming cells
  • protects bone
  • assists in fracture repair
  • nourishes bone tissue
  • attachment point for ligaments tendons
  • 6. medullary cavity
  • distal and proximal ends
  • 7. endosteum
  • thin connective tissue lines medullary cavity
  • contains bone-forming cells

14
Figure 6.2a
15
Figure 6.2b
16
Concept 6.4 Osseous Tissue
17
Osseous Tissue
  • contains abundant extracellular matrix
  • 25 water
  • 25 collagen fibers
  • 50 crystalized mineral salts
  • mainly hydroxapatite
  • deposited and calcified by osteoblasts
  • hardness depends on minerals
  • flexibility depends on collagen fibers

18
Cells of Osseous Tissue
  • Four Types
  • osteogenic cells
  • unspecialized stem cells
  • develop into osteoblasts
  • only bone cells to undergo division
  • osteoblasts
  • bone-building cells
  • synthesize and secrete collagen fibers
  • initiate calcification
  • become trapped in secretions and become osteocytes

19
Cells of Osseous Tissue
  • 3. osteocytes
  • mature bone cells
  • most numerous
  • maintain daily metabolism
  • nutrient and waste exchange
  • 4. Osteoclasts
  • huge cells derived from fusion monocytes (up to
    50!) concentrated in endosteum
  • release enzymes from lysosomes and acids that
    digest protein and mineral components
    (reabsorption)

20
Figure 6.3
21
Types of Osseous Tissue
  • Two types
  • compact bone
  • spongy bone

22
Types of Osseous Tissue
  • compact bone
  • few spaces
  • external surface of all bones
  • bulk of diaphysis in long bones
  • provides protection and support
  • resists stresses of weight bearing and movement

23
Anatomy of Compact Bone
  • osteons
  • matrix arranged in functional units called
    osteons or haversian systems
  • vessels and nerves penetrate through perforating
    or Volkmans canals
  • connect with those of
  • periosteum
  • central canal
  • medullary cavity
  • parallel along lines of stress
  • thickest at points of highest stress

24
Anatomy of Compact Bone
  • central canals
  • central canals run longitudinally through bone
  • surrounded by concentric lamellae
  • rings of calcified extracellular matrix
  • between lamellae are lacunae
  • contain osteocytes
  • lacunae connected by canaliculi
  • filled with extra cellular fluid
  • processes of osteocytes connected by cell
    junctions
  • provide routes for nutrient and waste exchange

25
Anatomy of Compact Bone
  • interstitial lamellae
  • between osteons
  • also have lacunae with osteocytes and canaliculi
  • fragments of older osteons destroyed during
    remodeling
  • circumferential lamellae
  • encircle bone
  • just beneath periosteum
  • around medullary cavity

26
Figure 6.4a
27
Types of Osseous Tissue
  • spongy bone
  • filled with red marrow
  • hip, ribs, sternum, vertebrae, ends of long bones
  • located where bones are not heavily stressed or
    stressed from many directions
  • makes up most of the bone tissue of short, flat,
    irregular, bones and of epiphyses of long bones
  • light

28
Anatomy of Spongy Bone
  • filled with red marrow
  • hip, ribs, sternum, vertebrae, ends of long bones
  • located where bones are not heavily stressed or
    stressed from many directions
  • makes up most of the bone tissue of short, flat,
    irregular, bones and of epiphyses of long bones
  • light

29
Anatomy of Spongy Bone
  • no osteons
  • trabeculae
  • lamellae arranged in irregular lattice
  • spaces between filled with red marrow
  • osteocytes lie in lacunae
  • canaliculi present between lacunae connecting
    osteocytes
  • support and protect red bone marrow

30
Figure 6.4 b-c
31
Concept 6.5 Blood Vessels and Nerves
32
Blood Vessels
  • periosteal arteries accompany nerves
  • enter diaphysis through perforating canals
  • large nutrient artery in center of diaphysis
  • enters diaphysis through nutrient foramen
  • divides into proximal and distal branches
  • metaphyseal arteries
  • enter ends of long bone and epiphyses

33
Blood Vessels and Nerves
  • periosteal veins accompany nerves
  • exit diaphysis with periosteal arteries
  • large nutrient vein in center of diaphysis with
    nutrient artery
  • exits diaphysis with nutrient artery
  • metaphyseal veins
  • drain ends of long bone and epiphyses
  • nerves accompany blood vessels
  • periosteum has many sensory nerves
  • sensitive to tearing and tension

34
Figure 6.2a
35
Concept 6.6 Bone Formation
36
Bone Formation
  • Ossification or osteogenesis
  • two major types
  • intramembranous ossification
  • endochondral ossification

37
Intramembranous Ossification
  • simpler of two methods
  • flat bones of skull and mandible formed this way
  • soft spots of fetal skull also formed this way
  • Figure 6.6

38
Figure 6.6
39
Endochondral Ossification
  • replacement of cartilage by osseous tissue
  • most bones formed this way
  • Figure 6.7

40
Figure 6.7
41
Concept 6.7 Bone Growth
42
Bone Growth
  • Length
  • occurs at epiphyseal plate
  • chondrocytes proliferate on epiphyseal side of
    plate while chondrocytes in older region are
    destroyed by calcification
  • cartilage is replaced by osseous tissue on
    diaphyseal side of plate
  • when osseous tissue produced faster than
    chondrocytes produce plate, bone growth slows
    (18-25 years of age)
  • epiphyseal plate replaced by epiphyseal line

43
Figure 6.8
44
Bone Growth
  • Thickness
  • deposition of osseous tissue on bone surface

45
Figure 6.9
46
Factors Affecting Bone Growth
  • adequate dietary intake of minerals
  • calcium
  • phosphorus
  • magnesium
  • vitamins A, C, D
  • sufficient levels of several hormone
  • weight bearing exercise
  • exercise that places stress on bones

47
Bone Growth Before Puberty
  • Insulin-like growth factors (IGFs)
  • produced by osseous tissue and liver
  • promote cell division at epiphyseal plate and in
    periosteum
  • production stimulated by human growth hormone
    (hGH) from pituitary gland
  • oversecretion of hGH produces giantism
  • undersecretion produces dwarfism
  • thyroid hormones and insulin also needed

48
Puberty and Beyond
  • surge in release of sex hormones
  • increases osteoblastic activity
  • responsible for growth spurt of puberty
  • females produce more estrogens
  • produces feminization of skeletal structures
  • males produce more androgens
  • produces masculinization of structures
  • both sexes produce estrogens which is ultimately
    responsible for conversion of epiphyseal plate
    into epiphyseal line

49
Concept 6.7 Bone Remodeling
50
Bone Remodeling
  • renews osseous tissue before deterioration sets
    in
  • rediscributes bone extracelluar matrix
  • repairs bond injuries
  • ongoing replacement of old osseous tissue by new
    osseous tissue
  • osteoclasts remove minerals and collagen
  • osteoblasts deposit minerals and collagen

51
Bone Remodeling
  • at any given time 5 of total bone mass in body
    is remodeled
  • renewal rates
  • compact bone 4 per year
  • spongy bone 20 per year
  • takes place at different rates in different
    regions
  • subjecting a bone to stress will make it stronger
  • osteoclastic and osteoblastic activity must be
    balanced

52
End Chapter 6
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