Skeletal System Part II

1
Skeletal System Part II

• Chapter 6

2
Microscopic Structures of Compact Bone

• Osteon (Haversian system) weight bearing
  pillars
• Central canal lined by endosteum, contains BVs
• Perforating (Volkmanns) canals connect blood
  and nerve supply of the peristeum to the central
  canal and marrow cavity
• Osteocytes spider-shaped mature bone cells
• Lacunae small cavities that contain osteocyte
  bodies
• Canaliculi (little canals) tubes that contain
  osteocyte legs
• connecting adjacent lacunae and capillaries
• Lamellae (little plate) - layer of bone matrix
  in which collagen fibers and mineral crystals
  align to run in a single direction
• - Concentric, Interstial, Circumferential

3
Microscopic Structure of Compact Bone
Fig 6.6
4
Spongy Bone

• Trabeculae contain several layers of lamelae and
  osteocytes but are too small for osteons or
  vessels
• Osteocytes receive nutrients from capillaries in
  the endosteum surround the trabeculae

Fig 6.8
5
Chemical Composition of Bone

• 35 organic components
• - cells, fibers, and organic substances
• - abundant collagen
• 65 inorganic mineral salts (hydroxyapatites)
• - primarily calcium phosphate crystals
• - pack tightly providing exceptional hardness
• - resists compression
• Bone is composed of the proper combination of
  organic and inorganic elements
• - durable, strong, and resilient without being
  brittle

6
Bone Development

• Ossification (osteogenesis) bone-tissue
  formation
• - embryo ? childhood ? adolescence ?full-grown
  skeleton
• - slower rate in adult as remodeling
• Intramembranous membrane bones developed from
  mesechyme (most skull bones and clavicles)
• - week 8, mesechyme cells cluster in CT to
  become osteoblasts that secrete organic bone
  matrix (osteoid)
• Endochondral bones (base of the skull down)
  that developed from hyaline cartilage
• - early week 8 bone begins as cartilage by end
  of week 8 pericondrium becomes vascularized to
  become bone-forming periosteum

7
Intramembranous Ossification
Fig 6.9
8
(No Transcript)
9
Endochondral Ossification
Fig 6.10
10
Anatomy of Epiphyseal Growth Areas

• In epiphyseal plates of growing bones cartilage
  is organized for quick, efficient growth
• - cartilage cells form tall stacks,
  chondroblasts at the top of stacks divide quickly
• - this pushes the epiphysis away from the
  diaphysis
• - lengthens entire long bone
• Older chondrocytes signal surrounding matrix to
  calcify, then they die and disintegrate
• - leaves long trabeculae of calcified cartilage
  on diaphysis side
• - trabeculae partially eroded by osteoclasts
• - osteoblasts then cover trabeculae with bone
  tissue
• - trabeculae trimmed away from their tips by
  osteoclasts

11
Epiphyseal Plate of Growing Long Bone
Fig 6.11
12
Endochondral Bone - Postnatal Growth

• In chldhood and adolescence bones lengthen
  entirely by growth of the epiphyseal plates
• Growth hormone produced by the pituitary gland
  stimulates epiphyseal plates
• Thyroid hormone ensures the the skeleton retains
  proper proportions
• Sex hormones (estrogen and testosterone) promote
  bone growth
• - later induces closure of epiphyseal plates

13
Adolescence to Adulthood

• At the end of adolescence, chondroblasts divide
  less often and epiphyseal plates become thinner
• - cartilage stops growing and is replaced by
  bone tissue
• Long bones stop lengthening when the diaphysis
  and epiphysis fuse
• Bone is dynamic living tissue
• - 500 mg of calcium may enter or leave the adult
  skeleton each day
• -
• Cancellous bone of the skeleton is replaced every
  3-4 years
• Compact bone is replaced every 10 years

14
Bone Remodeling

• Growing bones widen as they lengthen
• - osteoblasts add bone tissue to the external
  surface of the diaphysis
• - osteoclasts remove bone from the internal
  surface of the diaphysis
• Appositional growth growth of a bone by
  addition of bone tissue to its surface
• Bone deposit and removal
• - occurs at periosteal and endosteal surfaces
• Bone remodeling
• - bone deposition accomplished by osteoblasts
• - bone reabsorption accomplished by osteoclasts

15
Spongy Bone Remodeling
Fig 6.12
16
Osteoclast A Bone-Degrading Cell

• A giant cell with many nuclei
• Crawls along bone surfaces
• Breaks down bone tissue
• - secretes concentrated HCl
• - lysosomal enzymes are released

Fig 6.13
17
Repair of Bone Fractures

• Simple fracture bone breaks cleanly and does
  not penetrate the skin
• Compound fracture broken ends of the bone
  protrude through the skin
• Treatment by reduction - realignment of the
  broken bone ends
• - closed, bone ends coaxed back into position
• - open, bone ends are joined surgically with
  pins or wires

18
Stages of Healing a Fracture
Fig 6.14
19
(No Transcript)
20
(No Transcript)
21
(No Transcript)
22

• Characterized by low bone mass
• Bone reabsorption outpaces bone desposition
• Occurs most often in women after menopause

23
Skeleton Throughout Life

• Cartilage grows quickly in youth
• Skeleton shows fewer chondrocytes in the elderly
• Timetable from birth to death
• - mesoderm gives rise to embryonic mesenchyme
• - mesenchyme produces membranes and cartilage
• - membranes and cartilage ossify
• Skeleton grows until the age of 18-21 years
• - in children and adolescents bone formation
  exceeds rate of bone reabsorption
• - in old age reabsorption predominates
• - bone mass declines with age

24
Clincial Terms

• Osteomalacia bones are inadequately mineralized
• Rickets Vit D or calcium phosphate
• Pagets disease
• Bone Graft
• Bony Spur
• Osteosarcoma
• Ostealgia
• Osteomyelitis
• Pathologic Fracture
• Traction