Bones and skeletal tissues
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6. P A R T A. Bones and Skeletal Tissues. Function of Bones. Support – form the framework that supports the body and cradles soft organs Protection – provide a protective case for the brain, spinal cord, and vital organs Movement – provide levers for muscles. Function of Bones.

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Bones and skeletal tissues



Bones and Skeletal Tissues

Function of bones
Function of Bones

  • Support – form the framework that supports the body and cradles soft organs

  • Protection – provide a protective case for the brain, spinal cord, and vital organs

  • Movement – provide levers for muscles

Function of bones1
Function of Bones

  • Mineral storage – reservoir for minerals, especially calcium and phosphorus

  • Blood cell formation – hematopoiesis occurs within the marrow cavities of bones

Classification of bones by shape
Classification of Bones: By Shape

  • Long bones – longer than they are wide (e.g., humerus)

Figure 6.2a

Classification of bones by shape1
Classification of Bones: By Shape

  • Short bones

    • Cube-shaped bones of the wrist and ankle

    • Bones that form within tendons (e.g., patella)

Figure 6.2b

Classification of bones by shape2
Classification of Bones: By Shape

  • Flat bones – thin, flattened, and a bit curved (e.g., sternum, and most skull bones)

Figure 6.2c

Classification of bones by shape3
Classification of Bones: By Shape

  • Irregular bones – bones with complicated shapes (e.g., vertebrae and hip bones)

Figure 6.2d

Bone markings
Bone Markings

  • Bulges, depressions, and holes that serve as:

    • Sites of attachment for muscles, ligaments, and tendons

    • Joint surfaces

    • Conduits for blood vessels and nerves

Four types of bone cells
Four Types of Bone Cells

  • Osteoprogenitor cells

    • stem cells

  • Osteoblasts

    • produce new bone

      • Eventually become osteocytes

  • Osteocytes

    • mature bone cells

  • Osteoclasts

    • are involved in bone resorption (breaking down & releasing things like calcium into the bloodstream)

Gross anatomy of bones bone textures
Gross Anatomy of Bones: Bone Textures

  • Compact bone – dense outer layer

  • Spongy bone – honeycomb of trabeculae

Microscopic structure of bone compact bone
Microscopic Structure of Bone: Compact Bone

  • Haversian system, or osteon – the structural unit of compact bone

    • Lamella – weight-bearing, column-like matrix tubes composed mainly of collagen

    • Haversian, or central canal – central channel containing blood vessels and nerves

    • Volkmann’s canals – channels lying at right angles to the central canal, connecting blood and nerve supply of the periosteum to that of the Haversian canal

Microscopic structure of bone compact bone1
Microscopic Structure of Bone: Compact Bone

  • Osteocytes – mature bone cells

  • Lacunae – small cavities in bone that contain osteocytes

  • Canaliculi – hairlike canals that connect lacunae to each other and the central canal


  • Begins in the embryo and continues as the skeleton grows during childhood and adolescence.

  • Even after the adult bones have formed, ossification continues.

Intramembranous ossification
Intramembranous Ossification

  • From a connective tissue membrane into bone

Endochondral ossification
Endochondral Ossification

  • Begins with a hyaline cartilage model.

Epiphyseal line formation
Epiphyseal Line Formation

  • Endochondral ossification of a long bone occurs in progressive stages.

  • Bone growth is complete when each epiphyseal plate has ossified and the epiphyseal line has formed.

  • Depending on the bone, epiphyseal plate ossification occurs between the ages of 10 and 25 years.

Bone growth
Bone Growth

  • Interstitial growth occurs in the epiphyseal plate as chondrocytes undergo mitosis

  • Appositional growth occurs within the periosteum.

Bone remodeling
Bone Remodeling

  • Although adult bone size has been reached, the bone continues to reshape itself throughout a person’s lifetime in a constant process of bone resorption and deposition.

Bone remodeling1
Bone Remodeling

  • The continual deposition of new bone tissue and the removal (resorption) of old bone tissue.

Types of bone fractures
Types of Bone Fractures

  • Compound (open) – bone ends penetrate the skin

  • Impacted – one broken end driven into the other end of the bone

  • Pott’s – distal fibula

  • Colles’ – distal radius

Common types of fractures
Common Types of Fractures

  • Comminuted – bone fragments into three or more pieces; common in the elderly

  • Stress – broken but not displaced, not broken all the way through

Common types of fractures1
Common Types of Fractures

  • Greenstick – incomplete fracture where one side of the bone breaks and the other side bends; common in children

Stages in the healing of a bone fracture
Stages in the Healing of a Bone Fracture

  • Hematoma formation

    • A mass of clotted blood (hematoma) forms at the fracture site

Figure 6.13.1

Stages in the healing of a bone fracture1
Stages in the Healing of a Bone Fracture

  • Fibrocartilaginous callus forms

  • forms a few days after the fracture

Figure 6.13.2

Stages in the healing of a bone fracture2
Stages in the Healing of a Bone Fracture

  • Bony callus formation

    • New bone trabeculae appear in the fibrocartilaginous callus

    • Fibrocartilaginous callus converts into a bony (hard) callus

    • Bone callus begins 3-4 weeks after injury, and continues until firm union is formed 2-3 months later

Figure 6.13.3

Stages in the healing of a bone fracture3
Stages in the Healing of a Bone Fracture

  • Bone remodeling

    • Excess material on the bone shaft exterior and in the medullary canal is removed

    • Compact bone is laid down to reconstruct shaft walls

Figure 6.13.4

Effects of hormones
Effects of Hormones

  • Thyroid hormone stimulates bone growth.

  • Growth hormone and thyroid hormone regulate and maintain normal activity at the epiphyseal plates until puberty.

  • Calcitonin inhibits osteoclast activity.

Homeostatic imbalances
Homeostatic Imbalances

  • Osteoporosis

    • Group of diseases in which bone reabsorption outpaces bone deposit

    • Spongy bone of the spine is most vulnerable

    • Occurs most often in postmenopausal women

    • Bones become so fragile that sneezing or stepping off a curb can cause fractures

Osteoporosis treatment
Osteoporosis: Treatment

  • Calcium and vitamin D supplements

  • Increased weight-bearing exercise

  • Hormone (estrogen) replacement therapy (HRT) slows bone loss

  • Natural progesterone cream prompts new bone growth

  • Statins increase bone mineral density

Classification of bones
Classification of Bones

  • Axial skeleton – bones of the skull, vertebral column, and rib cage

  • Appendicular skeleton – bones of the upper and lower limbs, shoulder, and hip