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

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Essential Terms

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

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Introduction

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

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Concept 6.1Skeletal System Functions
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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

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Concept 6.2 Classification of Bones
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Bone Classification

• Shape
• long
• short
• flat
• irregular
• sesamoid

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Figure 6.1
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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

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Concept 6.3 Long Bones
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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

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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

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Figure 6.2a
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Figure 6.2b
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Concept 6.4 Osseous Tissue
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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

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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

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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)

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Figure 6.3
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Types of Osseous Tissue

• Two types
• compact bone
• spongy bone

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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

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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

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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

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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

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Figure 6.4a
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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

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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

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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

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Figure 6.4 b-c
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Concept 6.5 Blood Vessels and Nerves
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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

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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

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Figure 6.2a
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Concept 6.6 Bone Formation
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Bone Formation

• Ossification or osteogenesis
• two major types
• intramembranous ossification
• endochondral ossification

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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

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Figure 6.6
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Endochondral Ossification

• replacement of cartilage by osseous tissue
• most bones formed this way
• Figure 6.7

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Figure 6.7
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Concept 6.7 Bone Growth
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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

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Figure 6.8
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Bone Growth

• Thickness
• deposition of osseous tissue on bone surface

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Figure 6.9
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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

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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

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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

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Concept 6.7 Bone Remodeling
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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

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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

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End Chapter 6