Bone Tissue

Chapter 7

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– Support – Protection– Movement – Electrolyte balance – Acid-base balance– Blood formation

• Osseous tissue– Connective tissue with a hardened matrix

• Deposition of calcium phosphate and other minerals– Part of the composition of a bone

http://www.amersol.edu.pe/class09/_09pdelaf/7th/science/webpages/skeleton.html

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

– Osteoblasts• Bone-forming cells• Found along endosteum and

periosteum• Secrete osteocalcin

– Osteocytes• Former osteoblasts that have been

trapped in their lacunae• Maintain bony matrix• Strain sensors

– Octeoclasts• Bone-dissolving cells

• Matrix– composed of inorganic and

organic components

• Inorganic component– Hydroxyapaptite

• Composed mainly of CaPO4 salt

• 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

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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– Reserve cartilage– Cell proliferation– Cell hypertrophy– Calcification– Bone deposition

• Spongy bonenzdl.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

– 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