bones and skeletal tissues

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PowerPoint ® Lecture Slides prepared by Leslie Hendon University of Alabama, Birmingham C H A P T E R Copyright © 2011 Pearson Education, Inc. Part 2 6 Bones and Skeletal Tissues

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6. Bones and Skeletal Tissues. Bone Development. Ossification (osteogenesis)—bone-tissue formation Membrane bones —formed directly from mesenchyme Intramembranous ossification Other bones—develop initially from hyaline cartilage Endochondral ossification. Intramembranous Ossification. - PowerPoint PPT Presentation

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Page 1: Bones and Skeletal Tissues

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

Page 2: Bones and Skeletal 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

Page 3: Bones and Skeletal Tissues

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

Page 4: Bones and Skeletal Tissues

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

Page 5: Bones and Skeletal Tissues

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

Page 6: Bones and Skeletal Tissues

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

Page 7: Bones and Skeletal Tissues

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

Page 8: Bones and Skeletal Tissues

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

Page 9: Bones and Skeletal Tissues

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

Page 10: Bones and Skeletal Tissues

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

Page 11: Bones and Skeletal Tissues

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

Page 12: Bones and Skeletal Tissues

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

Page 13: Bones and Skeletal Tissues

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

Page 14: Bones and Skeletal Tissues

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

Page 15: Bones and Skeletal Tissues

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

Page 16: Bones and Skeletal Tissues

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

Page 17: Bones and Skeletal Tissues

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

Page 18: Bones and Skeletal Tissues

Copyright © 2011 Pearson Education, Inc.

Repair of Bone Fractures

• Simple and compound fractures• Treatment by reduction• Closed reduction• Open reduction

Page 19: Bones and Skeletal Tissues

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

Page 20: Bones and Skeletal Tissues

Copyright © 2011 Pearson Education, Inc.

Common Types of Fractures

Table 6.2 (1 of 3)

Page 21: Bones and Skeletal Tissues

Copyright © 2011 Pearson Education, Inc.

Common Types of Fractures

Table 6.2 (2 of 3)

Page 22: Bones and Skeletal Tissues

Copyright © 2011 Pearson Education, Inc.

Common Types of Fractures

Table 6.2 (3 of 3)

Page 23: Bones and Skeletal Tissues

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Disorders of Bones

• Osteoporosis• Characterized by low bone mass• Bone reabsorption outpaces bone

deposition• Occurs most often in women after

menopause

Page 24: Bones and Skeletal Tissues

Copyright © 2011 Pearson Education, Inc.

Osteoporosis

Figure 6.16

Page 25: Bones and Skeletal Tissues

Copyright © 2011 Pearson Education, Inc.

Disorders of Bones

• Osteomalacia• Occurs in adults—bones are inadequately

mineralized• Rickets• Occurs in children—analogous to

osteomalacia

Page 26: Bones and Skeletal Tissues

Copyright © 2011 Pearson Education, Inc.

Disorders of Bones

• Paget’s disease• Characterized by excessive rate of bone

deposition • Osteosarcoma• A form of bone cancer

Page 27: Bones and Skeletal Tissues

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

Page 28: Bones and Skeletal Tissues

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