Chapter 7
Bone Tissue
Objectives
• Know the functions of the skeletal system
• Understand how bones are classified
• Identify the macroscopic and microscopic features of bone
• Understand how bone is developed and physiologically
controlled
• Know what a fracture is and how it is repaired
• Know some bone disorders
Skeletal System
• Composed of bones, cartilages, and ligaments joined tightly
together to form a strong, flexible framework for the body
• Skeleton functions
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Support
Protection
Movement
Electrolyte balance
Acid-base balance
Blood formation
• Osseous tissue
http://www.amersol.edu.pe/class09/_09pdelaf/7th/science/webpages/skeleton.html
– Connective tissue with a hardened matrix
• Deposition of calcium phosphate and other minerals
– Part of the composition of a bone
Classification of Bones
• Classified based on shape and corresponding
function
• Four categories
– Long bones
– Short bones
– Irregular bones
– Flat bones
massasoit-bio.net
General Features of Bones
• Epiphysis
– Ends of the bone
– Composed of cancellous (spongy) bone
• Diaphysis
– Shaft of the bone
– Composed of compact bone
• Medullary cavity
– Contains yellow bone marrow
– Epiphyiseal plate
http://pathologyoutlines.com/bone.html
Structure of Bone
Figure 5.1
Histology
• Four main types of bone cells
– Osteogenic (osteoprogenitor) cells
• give rise to osteoblasts , osteocytes
• Matrix
– composed of inorganic and organic
components
– Osteoblasts
• Bone-forming cells
• Found along endosteum and
periosteum
• Secrete osteocalcin
• Inorganic component
– Hydroxyapaptite
• Composed mainly of CaPO4 salt
– Osteocytes
• Former osteoblasts that have been
trapped in their lacunae
• Maintain bony matrix
• Strain sensors
– Octeoclasts
• Bone-dissolving cells
• Organic components
– Protein and carbohydrate
• Collagen
• Bone is a composite
Compact Bone
• Osteon (haversian system)
– Basic structural unit of compact
bone
• Central (haversian) canal
surrounded by concentric
lamellae (matrix)
• Perforating canals
– Transverse or diagonal passages
into the central canal
– Originate at nutrient foramen
ask.com
Spongy Bone
• Composed by a network of
spicules and trabeculae
• Spaces filled with red
marrow
• Beams arranged to sustain
stress
commons.wikimedia.org
Bone Development
• Ossification or osteogenesis
– Formation of bone
• Two methods
– Intramembranous ossification
– Endochondral ossification
Intramembranous Ossification
• Produces flat bones of skull and clavicles
• Starts with
osteoid
• End with
diploe
massasoit-bio.net
Endochondral Ossification
• Bone develops from a hyaline model
trjohn.blogspot.com
Bone Growth and Remodeling
• Bone Elongation
– Involves epiphyseal plates
• Hyaline cartilage between to transitional zones (metaphysis)
• Zones of mataphysis
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Reserve cartilage
Cell proliferation
Cell hypertrophy
Calcification
Bone deposition
• Spongy bone
nzdl.org
Bone Growth and Remodeling
• Interstitial growth
– Result from growth of cartilage within the metaphysis
– Finite process
• Epiphyseal line
• Appositional growth
– Growth in diameter and thickness
• Circumferential lamellae
• Remodeling
– Wolff’s law of bone
• The architecture of bone is determined by the mechanical stresses
placed up it.
– Bone adapts to withstand stress
Physiology of Osseous Tissue
• Mineral deposition
– Calcium and phosphate are allowed to reach their
solubility product
• Precipitate in the matrix
– Ectopic ossification
• Abnormal calcification of soft tissue
– Calculus
• Mineral resorption
– HCl secreted by osteoclasts
– Acid phosphatase
• Absorbs collagen
Calcium Homeostasis
• Hypocalcemia
– Leads to excitability of nervous system
• Hypercalcimia
– Leads to depression of nervous system
Calcium Homeostasis
• Regulated by three hormones
– Calcitonin
• Secreted by parafollicular cells in thyroid
• Promote deposition of calcium in the bone
• Decreases calcium level in blood
– Inhibit osteoclasts, promote osteoblast activity
– Parathyroid hormone
• Secreted by parathyroid glands
• Promotes bone resorption
• Increases calcium level in blood
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Raise osteoclast population
Promotes calcium reabsorption in kidneys
Promotes calcitriol synthesis
Inhibits collagen deposition
– Calcitriol
• Increases calcium level in blood
– Promotes more calcium absorption by intestine
– Promotes reapsorption from skeleton
Fractures and Repair
• Fracture
– Break in the bone
– Two types
• Stress
• Pathological
• Table 7-2 for classifications
• Granulation tisssue
– Fibrous mass of
capillaries and cells
within hematoma
medical-definitions.com
Bone Disorders
• Osteoporosis
– Sever loss of bone density
• Osteoclast more active than osteoblasts
• Osteosarcoma
– Most common and deadly form of bone cancer
• Metastasizes quickly
• Osteogenesis imperfecta
– Brittle bones
• Defect in collagen deposition