6 Bones and Skeletal Tissues: Revised by Dr. Par Mohammadian

Overview Skeletal Cartilage Hyaline Fibrocartilage Elastic Classification of Bones Axial & Appendicular Long, short, flat, irregular Functions of Bones Bone Structure Gross Anatomy Short, flat, irregular long Microscopic Views Cells Compact & spongy bones Chemical Composition organic Inorganic Bone Development Bone Diseases © 2013 Pearson Education, Inc.

Skeletal Cartilages Three types Hyaline cartilage Elastic cartilage Provides support, flexibility, and resilience Collagen fibers only; most abundant type Articular, costal, respiratory, nasal cartilage Elastic cartilage Similar to hyaline cartilage, but contains elastic fibers External ear and epiglottis Fibrocartilage Thick collagen fibers—has great tensile strength Menisci of knee; vertebral discs © 2013 Pearson Education, Inc.

Figure 6.1 The bones and cartilages of the human skeleton. Epiglottis Thyroid cartilage Larynx Cartilage in external ear Cartilages in nose Cricoid cartilage Trachea Articular cartilage of a joint Lung Costal cartilage Cartilage in intervertebral disc Respiratory tube cartilages in neck and thorax Pubic symphysis Bones of skeleton Axial skeleton Meniscus (padlike cartilage in knee joint) Appendicular skeleton Cartilages Articular cartilage of a joint Hyaline cartilages Elastic cartilages Fibrocartilages © 2013 Pearson Education, Inc.

Classification of Bones Axial & Appendicular Skeletal Cartilage Hyaline Fibrocartilage Elastic Classification of Bones Axial & Appendicular Long, short, flat, irregular Functions of Bones Bone Structure Gross Anatomy Short, flat, irregular long Microscopic Views Cells Compact & spongy bones Chemical Composition organic Inorganic Bone Development Bone Diseases

Classification of Bones 206 named bones in skeleton Divided into two groups Axial skeleton Long axis of body Skull, vertebral column, rib cage Appendicular skeleton Bones of upper and lower limbs Girdles attaching limbs to axial skeleton © 2013 Pearson Education, Inc.

Figure 6.1 The bones and cartilages of the human skeleton. Epiglottis Thyroid cartilage Larynx Cartilage in external ear Cartilages in nose Cricoid cartilage Trachea Articular cartilage of a joint Lung Costal cartilage Cartilage in intervertebral disc Respiratory tube cartilages in neck and thorax Pubic symphysis Bones of skeleton Axial skeleton Meniscus (padlike cartilage in knee joint) Appendicular skeleton Cartilages Articular cartilage of a joint Hyaline cartilages Elastic cartilages Fibrocartilages © 2013 Pearson Education, Inc.

Classification of Bones by Shape Long bones Short bones Flat bones Irregular bones © 2013 Pearson Education, Inc.

Classification of Bones by Shape Long bones Longer than they are wide Limb, wrist, ankle bones Short bones Cube-shaped bones (in wrist and ankle) Sesamoid bones (within tendons, e.g., Patella) Vary in size and number in different individuals Flat bones Thin, flat, slightly curved Sternum, scapulae, ribs, most skull bones Irregular bones Complicated shapes Vertebrae, coxal bones © 2013 Pearson Education, Inc.

Figure 6.2 Classification of bones on the basis of shape. Flat bone (sternum) Long bone (humerus) Irregular bone (vertebra), right lateral view Short bone (talus) © 2013 Pearson Education, Inc.

Classification of Bones Axial & Appendicular Skeletal Cartilage Hyaline Fibrocartilage Elastic Classification of Bones Axial & Appendicular Long, short, flat, irregular Functions of Bones Bone Structure Gross Anatomy Short, flat, irregular long Microscopic Views Cells Compact & spongy bones Chemical Composition organic Inorganic Bone Development Bone Diseases

Seven important functions Functions of Bones Seven important functions Support: For body and soft organs Protection: For brain, spinal cord, &vital organs Movement Mineral and growth factor storage: Ca and phosphorus, and growth factors reservoir Blood cell formation (hematopoiesis) in red marrow cavities of certain bones Triglyceride (fat) storage Hormone production: Osteocalcin Regulates bone formation Protects against obesity, glucose intolerance, diabetes mellitus © 2013 Pearson Education, Inc.

Classification of Bones Axial & Appendicular Skeletal Cartilage Hyaline Fibrocartilage Elastic Classification of Bones Axial & Appendicular Long, short, flat, irregular Functions of Bones Bone Structure Gross Anatomy Short, flat, irregular long Microscopic Views Cells Compact & spongy bones Chemical Composition organic Inorganic Bone Development Bone Diseases

Three levels of structure Bones Are organs Contain different types of tissues Bone (osseous) tissue, nervous tissue, cartilage, fibrous connective tissue, muscle and epithelial cells in its blood vessels Three levels of structure Gross anatomy Microscopic Chemical Composition © 2013 Pearson Education, Inc.

Gross Anatomy Bone textures Compact and spongy bone Compact Dense outer layer; smooth and solid Spongy (cancellous or trabecular) Honeycomb of flat pieces called trabeculae © 2013 Pearson Education, Inc.

Structure of Short, Irregular, and Flat Bones Plates sandwiched between connective tissue membranes Periosteum (outer layer) and endosteum No shaft or epiphyses Bone marrow throughout spongy bone; no marrow cavity Spongy bone (diploë) Compact bone Trabeculae of spongy bone © 2013 Pearson Education, Inc.

Structure of Typical Long Bone Articular cartilage Diaphysis Tubular shaft forms long axis Compact bone surrounding medullary cavity Epiphyses Bone ends External compact bone; internal spongy bone Articular cartilage covers articular surfaces Between is epiphyseal line Remnant of childhood bone growth at epiphyseal plate Proximal epiphysis Spongy bone Epiphyseal line Periosteum Compact bone Medullary cavity (lined by endosteum) Diaphysis Distal epiphysis © 2013 Pearson Education, Inc.

Membranes: Periosteum Endosteum White, double-layered membrane Covers external surfaces except joint surfaces Osteogenic layer: Contains primitive stem cells – osteogenic cells Many nerve fibers and blood vessels Anchoring points for tendons and ligaments Yellow bone marrow Compact bone Periosteum Membranes: Endosteum Perforating (Sharpey’s) fibers covering internal bone surface Covers trabeculae of spongy bone Contains osteogenic cells that can differentiate into other bone cells Nutrient arteries © 2013 Pearson Education, Inc.

Hematopoietic Tissue in Bones Red marrow Found within trabecular cavities of spongy bone and diploë of flat bones (e.g., Sternum) In medullary cavities and spongy bone of newborns Adult long bones have little red marrow Heads of femur and humerus only Red marrow in diploë and some irregular bones is most active Yellow marrow can convert to red, if necessary © 2013 Pearson Education, Inc.

Bone marrow transplant

Sites of muscle, ligament, and tendon attachment on external surfaces Bone Markings Sites of muscle, ligament, and tendon attachment on external surfaces Joint surfaces Conduits for blood vessels and nerves Projections Depressions Openings Most indicate stresses created by muscle pull or joint modifications Depressions and openings Usually allow nerves and blood vessels to pass © 2013 Pearson Education, Inc.

Table 6.1 Bone Markings (1 of 2) © 2013 Pearson Education, Inc.

Table 6.1 Bone Markings (2 of 2) © 2013 Pearson Education, Inc.

Classification of Bones Axial & Appendicular Skeletal Cartilage Hyaline Fibrocartilage Elastic Classification of Bones Axial & Appendicular Long, short, flat, irregular Functions of Bones Bone Structure Gross Anatomy Short, flat, irregular long Microscopic Views Cells Compact & spongy bones Chemical Composition organic Inorganic Bone Development Bone Diseases © 2013 Pearson Education, Inc.

Microscopic Anatomy of Bone: Cells of Bone Tissue Five major cell types Each specialized form of same basic cell type Osteogenic cells Osteoblasts Osteocytes Bone lining cells Osteoclasts © 2013 Pearson Education, Inc.

Osteogenic Cells Osteoblasts Also called osteoprogenitor cells Mitotically active stem cells When stimulated differentiate into osteoblasts Osteoblasts Osteogenic cell Osteoblast Bone-forming cells Secrete unmineralized bone matrix or osteoid Includes collagen and calcium-binding proteins Actively mitotic Matrix-synthesizing cell responsible for bone growth Stem cell © 2013 Pearson Education, Inc.

Osteocytes Bone Lining Cells Osteoclasts Mature bone cells in lacunae bone matrix maintaining cells Bone Lining Cells Line surfaces where there is no bone activity Osteoclasts Derived from hematopoietic stem cells that become macrophages Bone destruction cells When active rest in resorption bay and have ruffled border Ruffled border increases surface area for enzyme degradation of bone © 2013 Pearson Education, Inc.

Osteocyte Osteoclast Mature bone cell that monitors and maintains the Figure 6.5c–d Comparison of different types of bone cells. Osteocyte Osteoclast Mature bone cell that monitors and maintains the mineralized bone matrix Bone-resorbing cell © 2013 Pearson Education, Inc.

Microscopic Anatomy of Bone: Compact Bone (lamellar bone) Artery with capillaries Structures in the central canal Vein Nerve fiber Lamellae Collagen fibers run in different directions Structural unit of compact bone: Osteon or haversian system: Consists of Central canal (haversian) surrounded by lamellae Perforating (volkmann's) canals Connect blood vessels and nerves of periosteum, medullary cavity, and central canal Lacunae—small cavities that contain osteocytes Canaliculi—hairlike canals that connect lacunae to each other and central canal Twisting force

Figure 6.7 Microscopic anatomy of compact bone. Spongy bone Central (Haversian) canal Perforating (Volkmann’s) canal Endosteum lining bony canals and covering trabeculae Osteon (Haversian system) Circumferential lamellae Perforating (Sharpey’s) fibers Lamellae Periosteal blood vessel Periosteum Nerve Vein Lamellae Artery Central canal Canaliculi Osteocyte in a lacuna Lacunae Interstitial lamella Lacuna (with osteocyte) © 2013 Pearson Education, Inc.

Microscopic Anatomy of Bone: Spongy Bone Appears poorly organized Trabeculae No osteons Contain irregularly arranged lamellae and osteocytes interconnected by canaliculi Capillaries in endosteum supply nutrients © 2013 Pearson Education, Inc.

Classification of Bones Axial & Appendicular Skeletal Cartilage Hyaline Fibrocartilage Elastic Classification of Bones Axial & Appendicular Long, short, flat, irregular Functions of Bones Bone Structure Gross Anatomy Short, flat, irregular long Microscopic Views Cells Compact & spongy bones Chemical Composition organic Inorganic Bone Development Bone Diseases

Chemical Composition of Bone: Organic Components Osteoid—1/3 of organic bone matrix secreted by osteoblasts Made of ground substance (proteoglycans and glycoproteins) Collagen fibers Contributes to structure; provides strength and flexibility Stretch and break easily on impact to prevent fracture © 2013 Pearson Education, Inc.

Chemical Composition of Bone: Inorganic Components Hydroxyapatites (mineral salts) 65% of bone by mass Mainly of tiny calcium phosphate crystals in and around collagen fibers Responsible for hardness and resistance to compression © 2013 Pearson Education, Inc.

Classification of Bones Axial & Appendicular Skeletal Cartilage Hyaline Fibrocartilage Elastic Classification of Bones Axial & Appendicular Long, short, flat, irregular Functions of Bones Bone Structure Gross Anatomy Short, flat, irregular long Microscopic Views Cells Compact & spongy bones Chemical Composition organic Inorganic Bone Development Bone Diseases

Ossification (osteogenesis) Bone Development Ossification (osteogenesis) Process of bone tissue formation Formation of bony skeleton Begins in 2nd month of development Postnatal bone growth Until early adulthood Bone remodeling and repair Lifelong © 2013 Pearson Education, Inc.

Two Types of Ossification Endochondral ossification Forms most of skeleton Bone forms by replacing hyaline cartilage Bones called cartilage (endochondral) bones Intramembranous ossification Forms flat bones, e.g. clavicles and cranial bones Bone develops from fibrous membrane Bones called membrane bones © 2013 Pearson Education, Inc.

Endochondral Ossification Forms most all bones inferior to base of skull Except clavicles Begins late in 2nd month of development Uses hyaline cartilage models Requires breakdown of hyaline cartilage prior to ossification © 2013 Pearson Education, Inc.

Figure 6.8 Endochondral ossification in a long bone. Week 9 Month 3 Birth Childhood to adolescence Articular cartilage Secondary ossification center Spongy bone Epiphyseal blood vessel Area of deteriorating cartilage matrix Epiphyseal plate cartilage Hyaline cartilage Spongy bone formation Medullary cavity Bone collar Blood vessel of periosteal bud Primary ossification center Bone collar forms around the diaphysis of the hyaline cartilage model. 1 Cartilage in the center of the diaphysis calcifies and then develops cavities. 2 The periosteal bud invades the internal cavities and spongy bone forms. 3 The diaphysis elongates and a medullary cavity forms. Secondary ossification centers appear in the epiphyses. 4 The epiphyses ossify. When completed, hyaline cartilage remains only in the epiphyseal plates and articular cartilages. 5 © 2013 Pearson Education, Inc.

Intramembranous Ossification Forms frontal, parietal, occipital, temporal bones, and clavicles Begins within fibrous connective tissue membranes formed by mesenchymal cells Ossification centers appear Osteoid is secreted Woven bone and periosteum form Lamellar bone replaces woven bone & red marrow appears © 2013 Pearson Education, Inc.

Figure 6.9 Intramembranous ossification. Slide 1 Mesenchymal cell Osteoblast Osteoid Collagen fibril Ossification center Osteocyte Newly calcified bone matrix Osteoid Osteoblast 1 Ossification centers appear in the fibrous connective tissue membrane. • Selected centrally located mesenchymal cells cluster and differentiate into osteoblasts, forming an ossification center that produces the first trabeculae of spongy bone. 2 Osteoid is secreted within the fibrous membrane and calcifies. • Osteoblasts begin to secrete osteoid, which calcifies in a few days. • Trapped osteoblasts become osteocytes. Fibrous periosteum Mesenchyme condensing to form the periosteum Osteoblast Plate of compact bone Trabeculae of woven bone Diploë (spongy bone) cavities contain red marrow Blood vessel 3 Woven bone and periosteum form. • Accumulating osteoid is laid down between embryonic blood vessels in a manner that results in a network (instead of concentric lamellae) of trabeculae called woven bone. • Vascularized mesenchyme condenses on the external face of the woven bone and becomes the periosteum. 4 Lamellar bone replaces woven bone, just deep to the periosteum. Red marrow appears. • Trabeculae just deep to the periosteum thicken. Mature lamellar bone replaces them, forming compact bone plates. • Spongy bone (diploë), consisting of distinct trabeculae, persists internally and its vascular tissue becomes red marrow. © 2013 Pearson Education, Inc.

Interstitial (longitudinal) growth Appositional growth Postnatal Bone Growth Interstitial (longitudinal) growth Increase in length of long bones Appositional growth Increase in bone thickness © 2013 Pearson Education, Inc.

Interstitial Growth: Growth in Length of Long Bones Requires presence of epiphyseal cartilage Epiphyseal plate maintains constant thickness Result of five zones within cartilage Resting (quiescent) zone Proliferation (growth) zone Hypertrophic zone Calcification zone Ossification (osteogenic) zone © 2013 Pearson Education, Inc.

Cartilage cells undergo mitosis. Figure 6.10 Growth in length of a long bone occurs at the epiphyseal plate. Resting zone 1 Proliferation zone Cartilage cells undergo mitosis. 2 Hypertrophic zone Older cartilage cells enlarge. 3 Calcification zone Matrix calcifies; cartilage cells die; matrix begins deteriorating; blood vessels invade cavity. Calcified cartilage spicule Osteoblast depositing bone matrix Osseous tissue (bone) covering cartilage spicules 4 Ossification zone New bone forms. © 2013 Pearson Education, Inc.

Interstitial Growth: Growth in Length of Long Bones Resting (quiescent) zone Cartilage on epiphyseal side of epiphyseal plate Relatively inactive Proliferation (growth) zone Cartilage on diaphysis side of epiphyseal plate Rapidly divide pushing epiphysis away from diaphysis  lengthening Hypertrophic zone Older chondrocytes -closer to diaphysis and their lacunae – enlarge  interconnecting spaces © 2013 Pearson Education, Inc.

Interstitial Growth: Growth in Length of Long Bones Calcification zone Surrounding cartilage matrix calcifies, chondrocytes die and deteriorate Ossification zone Chondrocyte deterioration leaves long spicules of calcified cartilage at epiphysis-diaphysis junction Spicules eroded by osteoclasts Covered with new bone by osteoblasts Ultimately replaced with spongy bone © 2013 Pearson Education, Inc.

Cartilage cells undergo mitosis. Figure 6.10 Growth in length of a long bone occurs at the epiphyseal plate. Resting zone 1 Proliferation zone Cartilage cells undergo mitosis. 2 Hypertrophic zone Older cartilage cells enlarge. 3 Calcification zone Matrix calcifies; cartilage cells die; matrix begins deteriorating; blood vessels invade cavity. Calcified cartilage spicule Osteoblast depositing bone matrix Osseous tissue (bone) covering cartilage spicules 4 Ossification zone New bone forms. © 2013 Pearson Education, Inc.

Interstitial Growth: Growth in Length of Long Bones Near end of adolescence chondroblasts divide less often Epiphyseal plate thins then is replaced by bone Epiphyseal plate closure Bone lengthening ceases Requires presence of cartilage Bone of epiphysis and diaphysis fuses Females – about 18 years Males – about 21 years © 2013 Pearson Education, Inc.

Appositional Growth: Growth in Width Allows lengthening bone to widen Occurs throughout life Osteoblasts beneath periosteum secrete bone matrix on external bone Usually more building up than breaking down  Thicker, stronger bone but not too heavy © 2013 Pearson Education, Inc.

Figure 6.10

Hormonal Regulation of Bone Growth Growth hormone Most important in stimulating epiphyseal plate activity in infancy and childhood Thyroid hormone Modulates activity of growth hormone Ensures proper proportions Testosterone (males) and estrogens (females) at puberty Promote adolescent growth spurts End growth by inducing epiphyseal plate closure Excesses or deficits of any cause abnormal skeletal growth © 2013 Pearson Education, Inc.

Bone Homeostasis Recycle 5-7% of bone mass each week Spongy bone replaced ~ every 3-4 years Compact bone replaced ~ every 10 years Older bone becomes more brittle Calcium salts crystallize Fractures more easily Consists of bone remodeling (Bone is continually deposited and resorbed in response to hormonal and mechanical stimuli) and bone repair © 2013 Pearson Education, Inc.

Bone Resorption Is function of osteoclasts Osteoclasts also Secrete lysosomal enzymes that digest matrix and protons (H+) Acidity converts calcium salts to soluble forms Osteoclasts also Phagocytize demineralized matrix and dead osteocytes Osteoclast activation involves PTH © 2013 Pearson Education, Inc.

Hormonal Control of Blood Ca2+ Parathyroid hormone (PTH) Produced by parathyroid glands Removes calcium from bone regardless of bone integrity Calcitonin may be involved Produced in thyroid gland In high doses lowers blood calcium levels temporarily © 2013 Pearson Education, Inc.

Other Hormones Affecting Bone Density Leptin Hormone released by adipose tissue Role in bone density regulation Inhibits osteoblasts in animals Serotonin Neurotransmitter regulating mood and sleep Secreted into blood after eating Interferes with osteoblast activity Serotonin reuptake inhibitors (e.g., Prozac) cause lower bone density © 2013 Pearson Education, Inc.

Classification of Bones Axial & Appendicular Skeletal Cartilage Hyaline Fibrocartilage Elastic Classification of Bones Axial & Appendicular Long, short, flat, irregular Functions of Bones Bone Structure Gross Anatomy Short, flat, irregular long Microscopic Views Cells Compact & spongy bones Chemical Composition organic Inorganic Bone Development Bone Diseases

Homeostatic Imbalances Osteoporosis Group of diseases Bone resorption outpaces deposit Spongy bone of spine and neck of femur most susceptible Vertebral and hip fractures common © 2013 Pearson Education, Inc.

Normal bone Osteoporotic bone Figure 6.16 The contrasting architecture of normal versus osteoporotic bone. Normal bone Osteoporotic bone © 2013 Pearson Education, Inc.

Risk Factors for Osteoporosis Most often aged, postmenopausal women 30% 60 – 70 years of age; 70% by age 80 30% caucasian women will fracture bone because of it Men to lesser degree Sex hormones maintain normal bone health and density As secretion wanes with age osteoporosis can develop © 2013 Pearson Education, Inc.

Treating Osteoporosis Traditional treatments Calcium Vitamin D supplements Weight-bearing exercise Hormone replacement therapy Slows bone loss but does not reverse it Controversial due to increased risk of heart attack, stroke, and breast cancer Some take estrogenic compounds in soy as substitute © 2013 Pearson Education, Inc.