PowerPoint® Lecture Slides prepared by Leslie HendonUniversity of Alabama, Birmingham
C H A P T E R
Copyright © 2011 Pearson Education, Inc.
Part 2
6Bones andSkeletal Tissues
Copyright © 2011 Pearson Education, Inc.
Bone Development
• Ossification (osteogenesis)—bone-tissue formation• Membrane bones—formed directly from
mesenchyme• Intramembranous ossification
• Other bones—develop initially from hyaline cartilage• Endochondral ossification
Copyright © 2011 Pearson Education, Inc.
Intramembranous Ossification
Figure 6.10, steps 1–2
MesenchymalcellCollagenfiberOssificationcenter
Osteoid
Osteoblast
Osteoid
Osteocyte
Newly calcifiedbone matrix
Osteoblast
Ossification centers appear in the fibrous connective tissue membrane.• Selected centrally located mesenchymal cells cluster
and differentiate into osteoblasts, forming an ossification center.
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.
1 2
Copyright © 2011 Pearson Education, Inc.
Intramembranous Ossification
Figure 6.10, steps 3–4
Mesenchymecondensingto form theperiosteum
Blood vessel
Trabeculae ofwoven bone
FibrousperiosteumOsteoblast
Plate ofcompact bone
Diploë (spongybone) cavitiescontain redmarrow
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 calledwoven bone.
• Vascularized mesenchyme condenses on the externalface of the woven bone and becomes the periosteum.
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.
3 4
Copyright © 2011 Pearson Education, Inc.
Endochondral Ossification
• All bones except some bones of the skull and clavicles
• Bones are modeled in hyaline cartilage• Begins forming late in the second month of
embryonic development• Continues forming until early adulthood
Copyright © 2011 Pearson Education, Inc.
Hyalinecartilage
Area ofdeterioratingcartilage matrix
Epiphysealblood vessel
Spongyboneformation
Epiphysealplatecartilage
Secondaryossificationcenter
Bloodvessel ofperiostealbud
Medullarycavity
Articularcartilage
Childhood to adolescenceBirthWeek 9 Month 3
Spongybone
Bone collarPrimaryossificationcenter
Bone collar forms around hyaline cartilage model.
Cartilage in the center of the diaphysis calcifies and then develops cavities.
The periosteal bud invades the internal cavities, and spongy bone begins to form.
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.
1 2 3 4 5
Stages in Endochondral Ossification
Figure 6.11
Copyright © 2011 Pearson Education, Inc.
Anatomy of Epiphyseal Growth Areas
• In epiphyseal plates of growing bones:• Cartilage is organized for quick, efficient
growth• Cartilage cells form tall stacks • Chondroblasts at the top of stacks divide
quickly• Pushes the epiphysis away from the diaphysis• Lengthens entire long bone
Copyright © 2011 Pearson Education, Inc.
Anatomy of Epiphyseal Growth Areas
• Older chondrocytes signal surrounding matrix to calcify
• Older chondrocytes then die and disintegrate• Leaves long trabeculae (spicules) of calcified
cartilage on diaphysis side• Trabeculae are partly eroded by osteoclasts• Osteoblasts then cover trabeculae with bone
tissue• Trabeculae finally eaten away from their tips
by osteoclasts
Copyright © 2011 Pearson Education, Inc. Figure 6.12
Organization of Cartilage within Epiphyseal Plate of Growing Long Bone
Calcified cartilagespicule
Osseous tissue
Resting zone
Proliferation zoneCartilage cells undergo mitosis.
Hypertrophic zoneOlder cartilage cells enlarge.
Ossification zoneNew bone formation is occurring.
Calcification zoneMatrix becomes calcified; cartilage cells die; matrix begins deteriorating.
1
2
3
4
Copyright © 2011 Pearson Education, Inc.
Postnatal Growth of Endochondral Bones
• During childhood and adolescence:• Bones lengthen entirely by growth of the
epiphyseal plates• Cartilage is replaced with bone CT as quickly
as it grows• Epiphyseal plate maintains constant thickness• Whole bone lengthens
Copyright © 2011 Pearson Education, Inc.
Hormonal Regulation of Bone Growth
• Growth hormone—produced by the pituitary gland• Stimulates epiphyseal plates
• Thyroid hormone—ensures that the skeleton retains proper proportions
• Sex hormones (estrogen and testosterone)• Promote bone growth• Later induces closure of epiphyseal plates
Copyright © 2011 Pearson Education, Inc.
Postnatal Growth of Endochondral Bones
• As adolescence draws to an end:• Chondroblasts divide less often• Epiphyseal plates become thinner• Cartilage stops growing• Replaced by bone tissue
• Long bones stop lengthening when diaphysis and epiphysis fuse
Copyright © 2011 Pearson Education, Inc.
Bone Remodeling
• Bone is dynamic living tissue• 500 mg of calcium may enter or leave the
adult skeleton each day• Cancellous bone of the skeleton is replaced
every3–4 years
• Compact bone is replaced every 10 years
Copyright © 2011 Pearson Education, Inc.
Postnatal Growth of Endochondral Bones
• Growing bones widen as they lengthen• Osteoblasts—add bone tissue to the external
surface of the diaphysis• Osteoclasts—remove bone from the internal
surface of the diaphysis• Appositional growth—growth of a bone by
addition of bone tissue to its surface
Copyright © 2011 Pearson Education, Inc.
Bone Remodeling
• Bone deposit and removal• Occurs at periosteal and endosteal surfaces
• Bone remodeling • Bone deposition—accomplished by
osteoblasts• Bone reabsorption—accomplished by
osteoclasts
Copyright © 2011 Pearson Education, Inc.
Remodeling, Spongy Bone
Figure 6.13
Compactbone
Spongy bone
Trabeculae of spongy bone
Resorption of bone matrix by osteoclasts
Deposition of new bone by osteoblasts
Newbone
OsteoblastOsteoblastOsteoclast
Copyright © 2011 Pearson Education, Inc.
Osteoclast—A Bone-Degrading Cell
• A giant cell with many nuclei• Crawls along bone surfaces• Breaks down bone tissue• Secretes
concentrated HCl• Lysosomal
enzymes are released
• Derived from hematopoietic stem cells
Figure 6.14
Osteocyte withina lacuna
Bone matrix
Ruffled borderof osteoclastNuclei
Copyright © 2011 Pearson Education, Inc.
Repair of Bone Fractures
• Simple and compound fractures• Treatment by reduction• Closed reduction• Open reduction
Copyright © 2011 Pearson Education, Inc.
Stages of Healing a Fracture
Figure 6.15
Hematoma Externalcallus
Newbloodvessels
Spongybonetrabecula
Internalcallus(fibroustissue andcartilage)
A hematoma forms. Fibrocartilaginous callus forms.
Bony callus forms.
Bonycallus ofspongyboneHealedfracture
Bone remodeling occurs.
1 2 3 4
Copyright © 2011 Pearson Education, Inc.
Common Types of Fractures
Table 6.2 (1 of 3)
Copyright © 2011 Pearson Education, Inc.
Common Types of Fractures
Table 6.2 (2 of 3)
Copyright © 2011 Pearson Education, Inc.
Common Types of Fractures
Table 6.2 (3 of 3)
Copyright © 2011 Pearson Education, Inc.
Disorders of Bones
• Osteoporosis• Characterized by low bone mass• Bone reabsorption outpaces bone
deposition• Occurs most often in women after
menopause
Copyright © 2011 Pearson Education, Inc.
Osteoporosis
Figure 6.16
Copyright © 2011 Pearson Education, Inc.
Disorders of Bones
• Osteomalacia• Occurs in adults—bones are inadequately
mineralized• Rickets• Occurs in children—analogous to
osteomalacia
Copyright © 2011 Pearson Education, Inc.
Disorders of Bones
• Paget’s disease• Characterized by excessive rate of bone
deposition • Osteosarcoma• A form of bone cancer
Copyright © 2011 Pearson Education, Inc.
The Skeleton Throughout Life
• Cartilage grows quickly in youth• Skeleton shows fewer chondrocytes in the
elderly• Bones are a timetable• Mesoderm• Gives rise to embryonic mesenchyme cells
• Mesenchyme• Produces membranes and cartilage
• Membranes and cartilage ossify
Copyright © 2011 Pearson Education, Inc.
The Skeleton Throughout Life
• Skeleton grows until the age of 18–21 years• In children and adolescents, bone formation
exceeds rate of bone reabsorption• In young adults, bone formation and bone
reabsorption are in balance• In old age, reabsorption predominates• Bone mass declines with age