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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.
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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
Cells of Mature Bone Figure 5.1 Structure of a Typical Bone
Compact and Spongy Bone - Histology Figure 5.2b,d The Internal Organization of Representative Bones
Functional Differences between Compact and Spongy Bone • Epiphyses, or ends • The diaphysis, or shaft • The metaphysis: • Connecting region between the epiphyses and diaphysis Figure 5.3a Anatomy of a Representative Bone
The Periosteum and Endosteum Figure 5.4 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 Human Growth Hormone (hGH): (Pituitary gland) Thyroxine: (Thyroid gland) Stimulate Osteoblasts Sex Hormones: (estrogen, progesterone, testosterone) (Ovaries and Testes) Calcitonin: Inhibits Osteoclasts (Thyroid gland) Parathyroid Hormone: (Parathyroid gland) Stimulates Osteoclasts Calcitriol: Increases Ca2+ absorption from intestine. (Skin and kidneys)
Bone disorders • Ricketts • Osteoporosis
Intramembranous Ossification [Insert fig 5.5] Figure 5.5 Intramembranous Ossification
ENDOCHONDRAL OSSIFICATION Animation
Endochondral Ossification • Bone development from hyaline cartilage • Bone growth in length • Shotgun Biology
Endochondral Ossification Figure 5.8 Epiphyseal Cartilages and Lines
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. STEPS OF ENDOCHONDRAL OSSIFICATION
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. STEPS OF ENDOCHONDRAL OSSIFICATION
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. STEPS OF ENDOCHONDRAL OSSIFICATION
7. Osteoblasts secrete osteoid around the remaining fragments of hyaline cartilage forming trabeculae of spongy bone. STEPS OF ENDOCHONDRAL OSSIFICATION
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. STEPS OF ENDOCHONDRAL OSSIFICATION
Epiphyseal plate LONGITUDINAL BONE GROWTH
Injury and Repair Figure 5.11 Fracture Repair
Bone Markings Table 5.1 Common Bone Marking Terminology
Classification of Bones Figure 5.13 Shapes of Bones
Bone Markings Figure 5.14 Examples of Bone Markings