The Skeletal System: Osseous Tissue and Skeletal Structure

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HUMAN ANATOMYFifth Edition

Chapter 1 Lecture

Chapter 6: Bones Skeletal Tissues

The Skeletal System:Osseous Tissue and Skeletal Structure

Introduction - components• The Bones - about 206

– Bone tissue, or osseous tissue, is the major component of the skeletal system.• Bones are dynamic organs made up of several

tissues types.

Introduction - Functions• The skeletal system has a variety of

functions:– Support: bones are the body’s infrastructure– Storage of minerals: calcium salts; 98% of the

body’s calcium is in the bones and adipose– Hematopoiesis: the bone marrow produces

new blood cells– Protection: many delicate organs are

surrounded by bone– Leverage: muscles pull on bone to produce

movement

Structure of Bone • Bones:

– Support connective tissues: • Cells • Solid matrix containing calcium salts

– hydroxyapaptite

– Outer covering called periosteum:• Continuous with the deep fascia

– Inner cellular lining is called the endosteum.

The Histological Organization of Mature Bone• The matrix:

– 2/3 of bone weight is calcium phosphate:• Hydroxyapatite crystals:

– Very resistant to compression

• Collagen fibers: – 1/3 of the bone matrix:

• Very resistant to stretch• Collagen and hydroxyapatite make bone

tissue extremely strong.• Cells account for about 2–3% of bone tissue.

Cells of Mature Bone• Osteocytes = mature cells:

– Maintain bone tissue • Osteoblasts immature, active cells:

– Found on inner and outer surfaces of a bone.– Osteoblasts produce osteoid.– The process of making new bone is called

osteogenesis.• Osteoprogenitor cells:

– Found on inner and outer surfaces of a bone.– Divide and differentiate to form new osteoblasts.

• Osteoclasts are giant multinucleated cells: – Perform osteolysis

Specialized Bone Cells

Figure 5.1 Structure of a Typical Bone

Cells of Mature Bone

Figure 5.2b,d The Internal Organization of Representative Bones

Compact and Spongy Bone - Histology

Compact Bone

Functional Differences between Compact and Spongy Bone

Figure 5.3a Anatomy of a Representative Bone

• Epiphyses, or ends• The diaphysis, or

shaft• The metaphysis:

– Connecting region between the epiphyses and diaphysis

Figure 5.4 The Periosteum and Endosteum

The Periosteum and Endosteum

Bone Development and Growth• Before six weeks of development the

skeleton is cartilage.• Osteogenesis is bone formation.

– Ossification is bone replacing existing tissue. • Calcification is the process of depositing

calcium salts into tissues.

Factors Regulating Bone Growth• Ions:

– Calcium, phosphate, magnesium, citrate, carbonate, sodium

• Vitamins:– Vitamins A and C– Vitamin D derivatives

Factors Regulating Bone Growth• Parathyroid hormone (PTH) acts to

increase overall availability of calcium ions in the blood.– Increased osteoclast activity is the direct

result of PTH levels. • Calcitonin is the antagonist of PTH. • Growth hormone and thyroxine increase

osteoblast activity leading to bone growth.• Sex hormones increase bone growth

dramatically during puberty.

Hormonal Control of Bone Tissue

Sex Hormones: (estrogen, progesterone, testosterone)

Calcitriol:

Human Growth Hormone (hGH):

Thyroxine:

Calcitonin:

Parathyroid Hormone:

(Thyroid gland)

(Parathyroid gland)

(Skin and kidneys)

(Ovaries and Testes)

(Pituitary gland)

Stimulate Osteoblasts

Inhibits Osteoclasts

Stimulates Osteoclasts

Increases Ca2+ absorptionfrom intestine.

Bone disorders• Ricketts• Osteoporosis

[Insert fig 5.5]

Figure 5.5 Intramembranous Ossification

Intramembranous Ossification

ENDOCHONDRAL OSSIFICATION

Animation

Endochondral Ossification• Bone development from hyaline cartilage• Bone growth in length• Shotgun Biology

Endochondral

Histology - epiphyseal plate

Figure 5.8 Epiphyseal Cartilages and Lines

Endochondral Ossification

STEPS OF ENDOCHONDRAL OSSIFICATION

•1. The perichondrium covering the hyaline cartilage “bone” is infiltrated with blood•vessels.

•2. Osteoblasts secrete osteoid against the hyaline cartilage diaphysis, encasing it in a bony collar.

•3. Chondrocytes within the diaphysis hypertrophy and the surrounding cartilage matrix starts to be calcified.

•4. The chondrocytes, however, die and the matrix begins to deteriorate.

•5. In month 3, the forming cavities are invaded by a collection of elements called the periosteal bud.

•6. The entering osteoclasts partially erode the calcified cartilage matrix.

• 7. Osteoblasts secrete osteoid around the remaining fragments of hyaline cartilage forming trabeculae of spongy bone.

• 8. As the primary ossification center enlarges, osteoclasts break down the newly formed spongy bone and open up a medullary cavity in the center of the diaphysis.

STEPS OF ENDOCHONDRAL OSSIFICATION•9. The epiphyses remain formed of cartilage until shortly before or after birth.

•10. Secondary ossification centers form in the epiphyses. The events of ossification are like the events of the diaphysis, except, that spongy bone mains in the internal and no medullary cavity forms.

LONGITUDINAL BONE GROWTH

Epiphysealplate

BONE GROWTH

Figure 5.11 Fracture Repair

Injury and Repair

Table 5.1 Common Bone Marking Terminology

Bone Markings

Figure 5.13 Shapes of Bones

Classification of Bones

Figure 5.14 Examples of Bone Markings

Bone Markings

The Skeletal System: Osseous Tissue and Skeletal Structure

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