Chapter 6: Bones and skeletal tissues (part b) provides knowledge of bone development, bone homeostasis, homeostatic imbalances of bone and developmental aspects of bones. After completing this chapter, students will be able to: Compare and contrast intramembranous ossification and endochondral ossification, describe the process of long bone growth that occurs at the epiphyseal plates,...and other contents.
PowerPoint® Lecture Slides prepared by Janice Meeking, Mount Royal College CHAPTER Bones and Skeletal Tissues: Part B Copyright © 2010 Pearson Education, Inc Bone Development • Osteogenesis (ossification)—bone tissue formation • Stages • Bone formation—begins in the 2nd month of development • Postnatal bone growth—until early adulthood • Bone remodeling and repair—lifelong Copyright © 2010 Pearson Education, Inc Two Types of Ossification Intramembranous ossification • Membrane bone develops from fibrous membrane • Forms flat bones, e.g clavicles and cranial bones Endochondral ossification • Cartilage (endochondral) bone forms by replacing hyaline cartilage • Forms most of the rest of the skeleton Copyright © 2010 Pearson Education, Inc Mesenchymal cell Collagen fiber Ossification center Osteoid Osteoblast Ossification centers appear in the fibrous connective tissue membrane • Selected centrally located mesenchymal cells cluster and differentiate into osteoblasts, forming an ossification center Copyright © 2010 Pearson Education, Inc Figure 6.8, (1 of 4) Osteoblast Osteoid Osteocyte Newly calcified bone matrix Bone matrix (osteoid) is secreted within the fibrous membrane and calcifies • Osteoblasts begin to secrete osteoid, which is calcified within a few days • Trapped osteoblasts become osteocytes Copyright © 2010 Pearson Education, Inc Figure 6.8, (2 of 4) Mesenchyme condensing to form the periosteum Trabeculae of woven bone Blood vessel Woven bone and periosteum form • Accumulating osteoid is laid down between embryonic blood vessels in a random manner The result is a network (instead of lamellae) of trabeculae called woven bone • Vascularized mesenchyme condenses on the external face of the woven bone and becomes the periosteum Copyright © 2010 Pearson Education, Inc Figure 6.8, (3 of 4) Fibrous periosteum Osteoblast Plate of compact bone Diploë (spongy bone) cavities contain red marrow Lamellar bone replaces woven bone, just deep to the periosteum Red marrow appears • Trabeculae just deep to the periosteum thicken, and are later replaced with mature lamellar bone, forming compact bone plates • Spongy bone (diploë), consisting of distinct trabeculae, persists internally and its vascular tissue becomes red marrow Copyright © 2010 Pearson Education, Inc Figure 6.8, (4 of 4) Endochondral Ossification • Uses hyaline cartilage models • Requires breakdown of hyaline cartilage prior to ossification Copyright © 2010 Pearson Education, Inc Month Week Childhood to adolescence Birth Articular cartilage Secondary ossification center Epiphyseal blood vessel Area of deteriorating cartilage matrix Hyaline cartilage Spongy bone formation Bone collar Primary ossification center Bone collar Epiphyseal plate cartilage Medullary cavity Blood vessel of periosteal bud Cartilage in the The periosteal forms around center of the hyaline cartilage diaphysis calcifies model and then develops cavities bud inavades the internal cavities and spongy bone begins to form Copyright © 2010 Pearson Education, Inc Spongy bone The diaphysis elongates and a medullary cavity forms as ossification continues Secondary ossification centers appear in the epiphyses in preparation for stage 5 The epiphyses ossify When completed, hyaline cartilage remains only in the epiphyseal plates and articular cartilages Figure 6.9 Week Hyaline cartilage Bone collar Primary ossification center Bone collar forms around hyaline cartilage model Copyright © 2010 Pearson Education, Inc Figure 6.9, step Stages in the Healing of a Bone Fracture Fibrocartilaginous callus forms • Phagocytic cells clear debris • Osteoblasts begin forming spongy bone within week • Fibroblasts secrete collagen fibers to connect bone ends • Mass of repair tissue now called fibrocartilaginous callus Copyright © 2010 Pearson Education, Inc External callus Internal callus (fibrous tissue and cartilage) New blood vessels Spongy bone trabecula Fibrocartilaginous callus forms Copyright © 2010 Pearson Education, Inc Figure 6.15, step Stages in the Healing of a Bone Fracture Bony callus formation • New trabeculae form a bony (hard) callus • Bony callus formation continues until firm union is formed in ~2 months Copyright © 2010 Pearson Education, Inc Bony callus of spongy bone Bony callus forms Copyright © 2010 Pearson Education, Inc Figure 6.15, step Stages in the Healing of a Bone Fracture Bone remodeling • In response to mechanical stressors over several months • Final structure resembles original Copyright © 2010 Pearson Education, Inc Healed fracture Bone remodeling occurs Copyright © 2010 Pearson Education, Inc Figure 6.15, step Hematoma Internal callus (fibrous tissue and cartilage) External callus New blood vessels Bony callus of spongy bone Healed fracture Spongy bone trabecula A hematoma forms Fibrocartilaginous Bony callus forms callus forms Copyright © 2010 Pearson Education, Inc Bone remodeling occurs Figure 6.15 Homeostatic Imbalances • Osteomalacia and rickets • Calcium salts not deposited • Rickets (childhood disease) causes bowed legs and other bone deformities • Cause: vitamin D deficiency or insufficient dietary calcium Copyright © 2010 Pearson Education, Inc Homeostatic Imbalances • Osteoporosis • Loss of bone mass—bone resorption outpaces deposit • Spongy bone of spine and neck of femur become most susceptible to fracture • Risk factors • Lack of estrogen, calcium or vitamin D; petite body form; immobility; low levels of TSH; diabetes mellitus Copyright © 2010 Pearson Education, Inc Copyright © 2010 Pearson Education, Inc Figure 6.16 Osteoporosis: Treatment and Prevention • Calcium, vitamin D, and fluoride supplements • Weight-bearing exercise throughout life • Hormone (estrogen) replacement therapy (HRT) slows bone loss • Some drugs (Fosamax, SERMs, statins) increase bone mineral density Copyright © 2010 Pearson Education, Inc Paget’s Disease • Excessive and haphazard bone formation and breakdown, usually in spine, pelvis, femur, or skull • Pagetic bone has very high ratio of spongy to compact bone and reduced mineralization • Unknown cause (possibly viral) • Treatment includes calcitonin and biphosphonates Copyright © 2010 Pearson Education, Inc Developmental Aspects of Bones • Embryonic skeleton ossifies predictably so fetal age easily determined from X rays or sonograms • At birth, most long bones are well ossified (except epiphyses) Copyright © 2010 Pearson Education, Inc Parietal bone Occipital bone Mandible Frontal bone of skull Clavicle Scapula Radius Ulna Ribs Humerus Vertebra Ilium Tibia Femur Copyright © 2010 Pearson Education, Inc Figure 6.17 Developmental Aspects of Bones • Nearly all bones completely ossified by age 25 • Bone mass decreases with age beginning in 4th decade • Rate of loss determined by genetics and environmental factors • In old age, bone resorption predominates Copyright © 2010 Pearson Education, Inc ... plates and articular cartilages Figure 6.9 Postnatal Bone Growth • Interstitial growth: • length of long bones • Appositional growth: • thickness and remodeling of all bones by osteoblasts and osteoclasts... forces or demands placed upon it • Observations supporting Wolff’s law: • Handedness (right or left handed) results in bone of one upper limb being thicker and stronger • Curved bones are thickest... blood Ca2+ levels Thyroid gland Osteoclasts degrade bone matrix and release Ca2+ into blood Copyright © 2010 Pearson Education, Inc Parathyroid glands PTH Parathyroid glands release parathyroid