Bones and Skeletal Tissues

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Bones and Skeletal Tissues

• Chapter 6 Part I

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Skeletal System Overview

• Adult skeleton consists of about 206 bones
• Skeleton - axial and appendicular
• Axial skeleton (80 bones) forms the bodys axis
  to support and protect head, neck, and trunk
  organs
• - Skull - composed of cranial facial bones
• - Vertebral column (backbone) 26 vertebrae,
  most separated by intervertebral discs
• - Rib cage 12 rib pairs, sternum, costal
  cartilages
• Appendicular skeleton - the limb bones and their
  girdles appended or attached to the axial skeleton

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Axial Skeleton
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Appendicular Skeleton
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Cartilages

• Cartilage is found throughout the adult human
  body
• External ear and epiglottis (keeps food from
  entering the larynx and lungs)
• Articular cartilages covers ends of most bones
  at movable joints (i.e. meniscus in knee)
• Costal cartilage connect ribs to the sternum
• Larynx, trachea, and nose
• Intervertebral discs and pubic symphysis

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Cartilage

• Far more abundant in the embryo than in the adult
• Contains no nerves or BVs
• Surrounded by perichondrium
• - a layer of dense irregular CT
• Consists primarily of water (60-80)
• Resilient tissue springs back to original shape

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Types of Cartilage

• Cartilage is a CT - consist of chondrocytes and
  an
• abundant EC matrix of fibers and a jellylike
  ground
• substance of glycoproteins that attract water
• Hyaline (glass) most abundant provides
  support through flexibility
• - nose, articular, costal, respiratory,
  embryonic skeleton
• Elastic contains many elastic fibers is able to
  tolerate repeatred bending
• - epiglottis, outer ear
• Fibrocartilage resists strong compression and
  strong tension
• - intervertebral discs, pubic symphysis, knee
  menisci

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Growth of Cartilage

• Appositional growth (growth from outside)
• - Condroblasts in the surrounding perichondrium
  produce new cartilage by actively secreting
  matrix
• Interstitial growth (growth from within)
• - Chondrocytes within cartilage divide secrete
  new matrix
• Cartilage stops growing in the late teens when
  the skeleton stops growing chondrocytes stop
  dividing
• - regenerates poorly in adults
• - limited healing due to ability of surviving
  chondrocytes to secrete more EC matrix

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Tissues in Bone

• Bones are organs - contain several types of
  tissues
• Dominated by bone CT
• Contain nervous tissue and blood CT
• Contain cartilage in articular cartilages
• Contain epithelial tissue lining of BVs

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Functions of Bones

• Support provides hard internal framework
• Movement - skeletal muscles attach to bones by
  tendons and use bones as levers to move the body
• Protection of underlying organs
• Mineral storage reservoir for minerals
• - most important are calcium and phosphate
• - released into bloodstream as ions (Ca2 ,
  PO42-)
• Blood-cell formation and energy storage
• - red bone marrow makes the blood cells
  (hematopoiesis)
• - yellow marrow is a site of fat storage

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Classification of Bones

• By shape as long, short, flat, or irregular
• Long bones - longer than wide (elongated shape)
• - a shaft plus 2 distinct ends (most bones in
  the limbs)
• Short bones roughly cube-shaped
• - occur in wrist and the ankle
• - sesamoid bones, a special type that forms
  within a tendon (i.e. patella) to reduce abrasion
  or tearing
• Flat bones - thin, flattened, usually curved
• - most cranial bones, ribs, sternum, scapula
• Irregular bones various shapes
• - vertebrae and hip bones

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Fig 6.2
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Gross Anatomy of Bones

• Compact bone dense outer layer of bone
• - looks smooth and solid
• Spongy or trabecuar bone internal network of
  bone
• a honeycomb of flat pieces called trabeculae
  (little beams)
• open spaces between trabeculae are filled with
  red or yellow bone marrow

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Structure of a Typical Long Bone

• Diaphysis or shaft - forms the long axis
• Epiphysis the bone ends
• - joint surface of each epiphysis is covered
  with a thin layer of articular cartilage
• Blood vessels well vascularized
• - nutrient artery and vein supplies the
  diaphysis
• - epiphyseal line between diaphysis and
  epiphysis in adults remnant of the childhood
  epiphyseal plate (hyaline disc)
• Medullary cavity hollow cavity filled with
  yellow marrow
• CT Membranes periosteum and endosteum

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Structure of a Long Bone
Fig 6.3
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Short, Irregular, Flat Bone Structure

• Have similar composition
• as long bones but are
• not cylindrical and have
• no diaphysis
• Contain bone marrow but no marrow cavity
• Diploe - internal spongy bone of flat bones

Fig 6.4
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Bone Design and Stress

• Anatomy of each bone reflects the stresses most
  often placed on it
• Subjected to compression as weight bears down or
  as muscles pull on them
• - loading off center
• Compression and tension greatest at external
  surfaces
• - so strong compact bone tissue occurs in
  external portions

Fig 6.5
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Bone Markings

• Superficial surfaces of bones reflect stresses
  placed on them
• There are 3 broad categories of bone markings
• - Projections for muscle attachment
• - Surfaces that form joints
• - Depressions and openings

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Projections

• Processes to which muscles and tendons attach to
• Trochanter - Very large bump
• Tuberosity - large roughened bump that a muscle
  attaches to
• Tubercle - small rounded bump
• Epicondyle - bump on the surface of a condyle
• Crest - narrow ridge
• Line - narrow ridge of bone, less prominent than
  a crest
• Spine - a sharp, slender raised area

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Joint Surfaces

• Bone surfaces that help form joints
• Head - end of bone supported by a constricted
  neck
• Facet - smooth, nearly flat articular surface
• Condyle - rounded, knucklelike bump that
  articulates with another bone
• Ramus - branchlike bar of bone

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Depressions and Openings

• Allows blood vessels and nerves to pass through
• Meatus - canal or long tubelike passageway
• Sinus air filled cavity
• Fossa - shallow depression or socket
• Sulcus - groove or furrow
• Fissure - narrow, slitlike opening
• Foramen - round or oval hole

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Table 6.1
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Microscopic Structure of Compact Bones