Function of Bones. Bone Tissue and Bones BONE CLASSIFICATION. Long Bones Gross Anatomy. Lab Activity 1 - Gross Anatomy of a Long Bone

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Bone Tissue and Bones

Bones form the framework of the skeleton.

Anatomy and Physiology Text and Laboratory Workbook, Stephen G.

Davenport, Copyright 2006, All Rights Reserved, no part of this publication can be used for any commercial purpose. Permission requests should be addressed to Stephen G. Davenport, Link Publishing, P.O. Box 15562, San

Antonio, TX, 78212

Function of Bones

• They function in providing: – (1) structural support,

– (2) attachment sites for tissues and organs, – (3) protection - especially for the brain and organs of

the chest,

– (4) a mineral storage site - especially for calcium and phosphorus,

– (5) a site (red bone marrow) for the production of the formed elements of blood, and

– (6) providing a site for fat deposit (yellow bone marrow).

BONE CLASSIFICATION

A general classification of bones is by their external shape. • Long bones

– Long bones are longer than they are wide.

• Short bones

– Short bones are boxy in shape.

• Flat bones

– Flat bones are thin and flattened.

• Irregular bones

– Irregular bones are irregular in shape, often with curved, pointed, and ridged surfaces.

Fig 10.1

Long Bones

Gross Anatomy

Long bones are longer than they are wide.

Lab Activity 1

-Gross Anatomy of a Long Bone

Observe a longitudinally sectioned femur. Know the following:

• Articular cartilage (removed; identify as to its placement)

• Compact bone • Diaphysis (shaft).

• Endosteum (removed; identify placement) • Epiphyseal line

• Epiphyses

• Medullary (marrow) cavity

• Periosteum (removed; identify placement) • Spongy bone

• Red bone marrow • Trabeculae • Yellow bone marrow

Fig 10.2

Lab Activity 1

-Gross Anatomy of a Long

Bone

Articular cartilage (removed; identify

as to its placement)

– Articular cartilage is hyaline cartilage that coves the end surfaces of the epiphyses where the bones form a joint.

Compact bone

– Compact bone is strong, dense bone that forms the diaphysis (shaft) of long bones and the exterior surfaces of all other bones.

Diaphysis (shaft)

– The diaphysis forms the longitudinal axis of the bone. It consists mostly of strong, dense bone called compact bone.

Fig 10.4

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Lab Activity 1

-Gross Anatomy of a Long Bone

• Endosteum (removed; identify as to its placement)

– The endosteum is a membrane that lines the medullary cavity, the trabeculae of spongy bone (mostly in the epiphyses), and extends into the central canals of the osteons (Haversian systems). The endosteum is composed mostly of osteoprogenitor cells, osteoblasts, and osteoclasts.

• Epiphyseal line

– An epiphyseal line is a line of bone formed by trabeculae at the site where a cartilage growth area, the epiphyseal plate, was located. The epiphyseal line in the distal epiphysis of the femur is the easiest to observe. Fig 10.2

Lab Activity 1

-Gross Anatomy of a Long Bone

• Epiphyses

– Epiphyses are the expanded ends of the long bone. The epiphyses are described as proximal or distal according to their respective closer or farther placement from the body. Their external surface is composed of thin, compact bone. Internally, they are composed of spongy bone.

• Medullary (marrow) cavity

– The medullary cavity is a large cavity within the diaphysis of a long bone and partially extends into the epiphyses. In adults, it contains mostly fatty (yellow) bone marrow.

Fig 10.2

Lab Activity 1

-Gross Anatomy of a Long Bone

Periosteum (removed; identify

placement)

– The periosteum is a membrane that covers the outer surface of the diaphysis and the epiphyses, except at their articular cartilage surfaces. The periosteum consists of an inner cellular layer and an outer fibrous layer. The cellular layer is composed mostly of osteoprogenitor cells (stem cells), bone-producing cells (osteoblasts), and bone-removing cells (osteoclasts.) The fibrous layer is mostly dense irregular connective tissue that provides attachment sites for tendons, ligaments, and into the bone itself by perforating fibers (Sharpey’s fibers) which penetrate the cellular layer into the matrix of compact bone.

Spongy bone

– Spongy bone is composed of thin plates of bone called trabeculae. Spongy bone is located in the epiphyses of long bones and forms the internal framework in all other bones.

Fig 10.2

Lab Activity 1

-Gross Anatomy of a Long Bone

• Red bone marrow

– Red bone marrow is located in the spongy bone tissue of the epiphyses of long bones and within the spongy bone tissue of all other bones. – Red bone marrow is the

tissue where the formed The formed elements enter into blood capillaries in the marrow.

Fig 10.4

Fig 21.6

Lab Activity 1

-Gross Anatomy of a Long Bone

• Trabeculae

– Trabeculae are thin plates of bone that form the internal framework of the epiphyses of long bones and most other bones. Trabeculae form an inner framework that is strong, light, and contains red bone marrow.

• Yellow bone marrow

– Yellow bone marrow is found within the medullary (marrow) cavity of long bones. It consists mostly of adipocytes and functions as a nutrient (fat) storage site.

Flat Bones

Gross Anatomy

A flat bone is characterized by being thin and flat, with an internal framework

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Flat Bone

• A flat bone is characterized by being thin and flat, with an internal framework of spongy (trabecular) bone. The surfaces of flat bones consist of compact bone.

Fig 10.5

MEMBRANES OF BONE

Two membranes are associated with bone, the

1. outer periosteum and the 2. inner endosteum.

Periosteum

• The periosteum is the outer covering of all bones except at their sites of articulations. • The periosteum functions

to

– (1) provide attachment sites for tendons and ligaments,

– (2) house the cells of bone, the osteoprogenitor cells, osteoblasts, and osteoclasts, and – (3) serve as a site for the

supply of nerves and blood vessels to the bone. Fig 10.6

Layers of the Periosteum

• The periosteum consists of two layers: • Fibrous Layer

– The outer fibrous layer of the periosteum is a dense regular connective tissue membrane consisting mostly of collagen fibers and fibroblasts. • Cellular Layer

– The inner cellular layer of the periosteum mostly functions as an osteogenic layer. Its cells are mostly osteoprogenitor cells, osteoblasts and osteoclasts, active in bone growth and remodeling.

Layers of the Periosteum

• Fig 10.7 A cross-section of compact bone (diaphysis) and its associated periosteum (100x). The fibrous layer of the periosteum is interwoven into the collagen fibers of a tendon. Collagen fibers called perforating fibers (not shown) extend from the fibrous periosteum into the matrix of bone. This collagenous organization makes an extremely strong attachment.

Endosteum

• The inner membranous covering associated with bone is the endosteum.

• The endosteum, a single cellular layer, is found lining

– (1) the medullary (marrow) cavity, – (2) the trabeculae, and

– (3) the surfaces of the central canals.

• The cells of the endosteum are osteoprogenitor cells, osteoblasts, and osteoclasts. The endosteum is active in bone growth and remodeling.

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Endosteum

Figure 10.8

• A cross-section of compact bone (diaphysis) and its associated membranes, the periosteum and endosteum. The endosteum is a single cellular layer found lining the medullary cavity, the trabeculae, and the central canals. The endosteum consists mostly of osteoblasts and osteoclasts.

BONE TISSUE AND

STRUCTURE

Two types of bone tissue are found in bones: 1. compact and

2. Spongy.

Both types have an extracellular framework, the matrix, which exhibits considerable hardness and tensile

strength.

Matrix of Bone Tissue

The extracellular framework of bone, the matrix, consists of both inorganic

and organic components.

Matrix – Inorganic Component

• The inorganic component of bone tissue

(about two-thirds) is mineral salts, mostly

the calcium salt hydroxyapatite, a crystal

form of calcium phosphate.

– Mineral salts make the matrix hard and noncompressible.

Matrix – Inorganic Component

Figure 10.10 • A photograph of a

bone that was heated to remove its organic constituents. The loss of the strong collagen fibers produced a brittle bone containing calcium salts.

Matrix – Organic Component

• The organic components of the matrix

(about one-third) are mostly collagenous

fibers produced by bone-forming cells, the

osteoblasts.

– Collagen fibers provide a framework for the deposition of hydoxyapatite crystals and give the matrix great tensile strength.

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Matrix – Organic Component

• Figure 10.9

A photograph of a fibula (leg bone) which was demineralized by a weak acid, then tied into a knot. The acid dissolved the mineral salts leaving the rubbery, flexible collagen framework of the bone.

Compact Bone

Compact bone is dense and is

found where strength is needed.

Compact Bone

• Compact bone is dense and is found where strength is needed. It makes up the external surfaces of all bones and forms the diaphysis (shaft) of long bones. • The structural units of

compact bone are

osteons (Haversian

systems). Fig 10.13

Osteon

An osteon is the structural unit of compact bone. Each osteon consists of concentric layers of matrix (lamellae) around a central canal lined with endosteum. Each central canal houses blood vessels and sometimes a nerve.

Fig 10.12

Osteon

• The osteons are usually parallel, and when shown in cross section, each system is seen as a region of concentric layers (lamellae) of matrix surrounding a central canal.

• Osteocytes, each in a small cavity called a lacuna, are scattered between the lamellae of each osteon. • Filling the spaces between adjacent osteons are regions

called interstitial lamellae. Interstitial lamellae are remnants of older osteons that were destroyed during bone remodeling.

• Lamellae called circumferential lamellae encircle the outer and inner regions of the bone.

Lamellae

• A layer of lamellae, the inner

circumferential lamellae, encircle the inner portion of a bone.

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Perforating and Central Canals

• Perforating canals – Small canals called

perforating canals (canals of Volkmann) extend inward, deep into the bone. The perforating canals bring blood vessels into the central canals and to the bone marrow. • Central Canals

– Each central canal contains one or more blood vessels and occasionally a nerve.

Fig 10.13

Canaliculi

• Small interconnecting canals called canaliculi pierce the matrix. • The canaliculi

interconnect the lacunae and the central canals. • Canaliculi are pathways

for branches of the osteocytes and their surrounding interstitial fluid.

– Through interstitial fluid and the interconnection of their branches (gap junctions), the osteocytes maintain communication with the blood vessels

located in the central canal. Fig 10.12

Lab Activity 2

Bone - Ground

• Observe a tissue preparation of compact bone labeled “Bone, ground.” • Ground bone tissue in

cross-section (43x) shows many osteons. Each osteon has a centrally located Haversian (central) canal. Fig 10.14

Lab Activity 2

Bone - Ground

• Each osteon (Haversian system) contains a centrally located central canal. In the matrix are concentric rows of osteocytes. Small canals, the canaliculi, contain branches of the osteocytes. Figure 10.15

Lab Activity 3

Bone - Demineralized

• Observe a tissue preparation labeled “Bone, demineralized.” • Demineralized bone tissue (100x) shows numerous osteocytes surrounded by collagen fibers. The central canal is lined with the endosteum and contains

blood vessels. Figure 10.16

Spongy Bone

Spongy (trabecular) bone is located in the epiphyses of long bones and forms

the internal framework of all other bones.

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Spongy bone

• Spongy (trabecular) bone is located in the epiphyses of long bones and forms the internal framework of all other bones.

– Spongy bone is made up of numerous interconnecting bony plates called trabeculae. The trabeculae are organized in an open framework that provides considerable strength with reduced weight. Their open framework provides a site for red bone marrow.

Figure 10.17

Cells of Bone Tissue

Types of bone cells are (1) osteoprogenitor,

(2) osteoblasts, (3) osteocytes, and

(4) osteoclasts.

Osteoprogenitor cells

• Osteoprogenitor cells are bone stem cells that undergo mitosis. Some of the daughter cells remain as osteoprogenitor cells, and the remaining daughter cells differentiate into osteoblasts.

• Osteoprogenitor cells are found in the cellular layer of the periosteum and in the endosteum. • Osteoprogenitor are important in maintaining a

population of osteoblasts for bone growth and repair.

Osteoblasts

• Osteoblasts are the building cells of bone matrix and are located in the cellular layer of the periosteum and in the endosteum.

• They are actively involved in the production of the organic portion of the matrix, the osteoid, which consists mostly of collagenous fibers.

• Additionally, the activity of osteoblasts promotes the

calcification of the osteoid to form bone tissue.

Osteoblasts may become completely surrounded by matrix and differentiate into osteocytes.

Figure 10.18

Osteocytes

• Osteocytes, the mature maintenance cells of bone tissue, are the most abundant of the bone cells.

• Osteocytes are not mitotically active and are located within the bone matrix within small cavities called lacunae.

– Small canals, the canaliculi, extend from and interconnect the lacunae.

Figure 10.19

Osteocytes

• Osteocytes (430x) are found within the matrix of bone. Cell branches interconnect the osteocytes by gap junctions and along with the interstitial fluid, which surrounds the osteocytes and their branches, permits exchange of nutrients, gases, etc.

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Osteoclasts

• Osteoclasts are cells that breakdown bone matrix. Osteoclasts are large multinucleate cells found in the cellular layer of the periosteum and in the endosteum. • They function in the

breakdown of bone matrix (osteolysis) mostly to

– remodel bone and to – maintain blood calcium ion

levels.

Figure 10.21

BONE DEVELOPMENT and

GROWTH

The skeleton begins as an embryonic framework composed of hyaline cartilage and fibrous membranes.

Ossification

Ossification is the formation and

development of bone tissue.

Ossification

• The formation and development of bone

tissue, ossification, eventually form the

mature bones of the skeleton.

• Osteogenesis, the production of bone

forming tissue, begins about six weeks

after fertilization with the differentiation of

stem cells into osteoprogenitor cells.

Ossification

• Calcification is the deposition of calcium

salts and occurs in a wide variety of

tissues including bone. In bone formation,

calcification occurs with the deposit of

hydroxyapatite (mostly calcium phosphate)

in the organic portion of the matrix, the

osteoid, and produces a calcified matrix. In

other tissues, calcification produces

calcified tissues.

Two Types of Ossification

The embryonic skeleton undergoes ossification by two processes:

1. Intramembranous ossification

– Intramembranous ossification occurs within fibrous membranes and produces flat bones. Flat bones, such as the bones of the roof of the skull, are produced by intramembranous ossification. 2. Endochondral ossification

– Endochondral ossification replaces a hyaline cartilage framework. Most bones of the skeleton are produced by this method. Long bones, such as the femur, humerus, tibia, etc., are excellent examples of endochondral ossification.

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Two Types of Ossification

Figure 10.22

• This specially prepared and stained animal demonstrates the early stages of bone development.

– Intramembranous ossification produces flat bones replaces fibrous membranes and produces flat bones.

– Endochondral ossification replaces the hyaline cartilage framework that forms most bones of the body.

Intramembranous Ossification

Intramembranous ossification occurs within fibrous membranes

and produces flat bones.

Intramembranous Ossification

Intramembranous ossification occurs within and replaces fibrous membranes to form flat bones.

• The process:

1. Mesenchymal cells (undifferentiated cells of mesodermal origin) within the fibrous membrane differentiate into osteoprogenitor cells.

2. Osteoprogenitor cells undergo mitosis to maintain a stem cell population.

3. Some of the daughter cells differentiate into osteoblasts, which begin the process of ossification.

4. Ossification sites, called centers of ossification, develop as the osteoblasts secrete the organic portion, the osteoid, of the bone matrix.

5. The osteoblasts that become completely surrounded (entrapped) by osteoid promote the process of calcification and differentiate into osteocytes. • Osteoprogenitor cells remain in a cellular layer at the

surface of the matrix where they function as stem cells.

Intramembranous Ossification

• The formation of ossification centers in intramembranous ossification (430x) occurs with the entrapment of osteoblasts in the osteoid. Figure 10.23

Intramembranous Ossification

• Intramembranous ossification (100x) continues with the production of spongy bone tissue with the formation of bony plates called trabeculae. Trabeculae are produced from the continued activity of osteoblasts.

•Figure 10.24

Intramembranous Ossification

Mature Flat Bone

• Cross section of the sternum, a flat bone. • A flat bone is characterized by parallel surfaces of compact bone separated by a layer of spongy bone. Figure 10.25

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Lab Activity 4

Intramembranous Ossification

• Observe a microscope slide preparation labeled “Intramembranous Ossification.” • Intramembranous ossification (100x) occurs within a fibrous (mesenchyme) membrane. Plates of bone, the trabeculae, are produced by the activity

of osteoblasts. Figure 10.26

Lab Activity 5

Fetal Skull

• Intramembranous ossification

can be observed in the fetal skull.

• Initially, intramembranous ossification of the flat bones (such as the parietals) produces

– (1) a thick region of bone at the ossification centers, – (2) areas of large, fibrous membranes, the fontanels, between the developing bones, and – (3) developing sutures,

regions of fibrous membrane between the articulating bones.

Figure 10.27

Figure 10.27

Fontanels

• Anterior (frontal) fontanel

– The anterior fontanel (frontal fontanel) is located midline between the two segments of the frontal bone and the paired parietals.

• Posterior (occipital) fontanel

– The posterior (occipital) fontanel is located midline between the paired parietals and the occipital bone.

• Sphenoid (anterolateral) fontanels

– The sphenoid (anterolateral) fontanels are located anteriorly and laterally, one on each side of the skull, and formed at the junction of the parietal, frontal, temporal, and sphenoid bones.

• Mastoid (posterolateral) fontanels

– The mastoid (posterolateral) fontanels are located posteriorly and laterally, one on each side of the skull, and formed at the junction of the parietal, occipital, and temporal bones.

ENDOCHONDRAL

OSSIFICATION

Most bones of the body are formed by

endochondral ossification.

Endochondral Ossification

• Endochondral ossification begins with the

replacement of hyaline cartilage of the

embryonic skeleton. Throughout the

process of endochondral ossification,

hyaline cartilage continues to serve as the

site and the model for the formation of

bone tissue.

Primary Ossification Center and

Bony Diaphysis

• In early development, endochondral ossification begins in an area in the diaphysis of the hyaline cartilage model called the primary

ossification center.

• Before endochondral ossification begins the perichondrium (a fibrous membrane that surrounds the cartilage) is converted into the periosteum and forms a bony collar.

• As the bony collar develops, the cartilage cells (chondrocytes) in the center of the shaft

1. enlarge (hypertrophy), and

2. their surrounding matrix calcifies. The calcification of the cartilage matrix results in the inability of nutrients to diffuse to the chondrocytes. 3. The chondrocytes die, and their surrounding

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Deterioration of Hyaline Cartilage

• A collar of bone forms around the diaphysis of the hyaline cartilage model.

• Cartilage cells undergo hypertrophy and the surrounding matrix calcifies. • Calcification blocks

nutrient delivery and cartilage cells deteriorate producing cavities.

Figure 10.29

Primary Ossification Center

• Blood vessels from the periosteum of the bony collar invade the cavities and form capillary networks.

• Blood brings in osteoprogenitor cells, which divide to produce osteoblasts.

• Osteoblasts begin to secrete bone matrix (osteoid) and ossification begins with the formation of bone trabeculae. • This area, the primary

ossification center, is the first

place where bone matrix is formed and consists of spongy bone tissue.

Figure 10.30

Formation of Bony Diaphysis

• Within a short time, a bony diaphysis is formed with two distinctive areas of hyaline cartilage, one at each end of the diaphysis, the cartilage epiphyses.

• Two metaphyses, regions of transformation of cartilage into bone, develop at the proximal and distal regions between each epiphysis and the diaphysis.

Figure 10.30

Lab Activity 6

Early Endochondrial Ossification

• Observe a microscope slide preparation labeled “Early Endochondral Ossification.”

Figure 10.31

Typical preparations (15x) used in the study of the primary ossification center.

Lab Activity 6

Early Endochondrial Ossification

• A hyaline cartilage model will serve as the site for endochondral ossification. In this specimen, no ossification has occurred. Figure 10.32

Lab Activity 7

Endochondrial Ossification

• Observe a microscope slide preparation labeled “Endochondral Ossification.” • Figure 10.33 – The formation of bone tissue (43x) begins at the primary ossification center.

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Lab Activity 7

Endochondrial Ossification

• The primary ossification center has developed into a bony diaphysis (15x). • Hyaline cartilage remains

at the ends in the regions called the epiphyses. • The metaphyses are

regions of tissue transformation. The metaphysis is located between the diaphysis and each epiphysis.

Figure 10.34

Secondary Ossification Center

• In the center of the hyaline cartilage epiphyses, sites called secondary

ossification centers begin to

develop.

• A secondary ossification center is formed when

1. blood vessels from the periosteum bud into the hyaline cartilage of the epiphyses.

2. Osteoprogenitor cells and osteoblasts arrive. 3. The deposition of osteoid by

osteoblasts activity begins the formation of trabeculae and produce a central region of spongy bone.

Figure 10.35

Secondary Ossification Center

• At the secondary ossification centers, blood vessels from the periosteum invade the cavities in the hyaline cartilage and form capillary networks. • Osteoclasts and

osteoblasts arrive and begin to modify the area into spongy bone.

Figure 10.36

Articular Cartilage and Epiphyseal Plate

At each epiphysis, the

spongy bone continues to enlarge until two distinctive areas of hyaline cartilage remain. • Articular cartilage

– The permanent outer cartilage area is the

articular cartilage

• Epiphyseal Plate

– The inner cartilage area is a disc-like plate, the

epiphyseal plate.

Figure 10.37

Lab Activity 8

Secondary Ossification Center

• Observe a microscope slide preparation labeled “Secondary Ossification Center.” • In Fig. 10.38 a secondary ossification center (20x) is shown in the epiphysis.

Lab Activity 8

Secondary Ossification Center

Figure 10.39

• A secondary ossification center (100x) is shown in the epiphysis. The replacement of the epiphyseal hyaline cartilage leaves two areas of hyaline cartilage, an outer articular cartilage and an inner epiphyseal cartilage plate.

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Growth of the Diaphysis

Bone growth occurs in two areas and produces two types of growth:

(1) growth in length, or longitudinal growth, and (2) growth in diameter, or appositional growth.

Growth of the Diaphysis

• Longitudinal growth

– Longitudinal growth, which results in an increase in length, occurs at the metaphysis, or the epiphyseal plate (observed in children and adolescents).

• Appositional growth

– Appositional growth, which results in an increase in diameter, occurs at the cellular (osteogenic) layer of the periosteum.

Longitudinal Growth

Longitudinal growth, which results in an increase in length, occurs at the metaphysis, or the epiphyseal plate (observed in children and adolescents).

Lab Activity 9

Growth of the Diaphysis

• Observe a slide preparation labeled “Endochondral Ossification.” • Figure 10.40 shows longitudinal growth of the diaphysis (100x). – Longitudinal growth occurs at the region of transformation, the metaphysis.

Figure 10.40

Lab Activity 9

Growth of the Diaphysis

• In the near central area of the epiphysis, the hyaline cartilage is described as the area of proliferation; the hyaline cartilage mitotically divides. • Older cartilage cells

(toward the diaphysis) undergo hypertrophy (enlargement) and the matrix of the cartilage

calcifies. Figure 10.40

Metaphysis

The metaphysis is the region where bone replaces hyaline cartilage and results in an increased length of the diaphysis, longitudinal growth.

• At the epiphyseal region of the metaphysis,

– (1) the cartilage cells die, – (2) most of the matrix

degenerates, and

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Metaphysis

• At the diaphysis surface of the metaphysis,

– (1) osteoblasts secrete bone matrix on remaining cartilage spicules and – (2) a network of bony trabeculae forms the diaphysis.

• In this manner, the bone continues to increase in length by forming bony trabeculae as the cartilage is removed.

Figure 10.40

Metaphysis / Early Epiphyseal Plate

• A secondary ossification center (100x) is shown in the epiphysis. The replacement of the epiphyseal hyaline cartilage leaves two areas of hyaline cartilage, an outer articular cartilage and an inner epiphyseal cartilage plate.

Figure 10.41

Epiphyseal Line

• The epiphyseal plates are completely removed (longitudinal growth is terminated), and a line of bone, called the epiphyseal

line, marks their prior

location.

Figure 10.42

Lab Activity 10

Epiphyseal Plates

Observe an x-ray of a long bone from an adolescent for the identification of epiphyseal plates. • Epiphyseal plates are

shown in this x-ray (Fig. 10.43) of an adolescent. Individual bones have specific times when their epiphyseal plates are replaced by bone tissue.

Figure 10.43

Lab Activity 11

Epiphyseal Lines

• Under the influence of hormones, especially the sex hormones produced in increasing amounts at puberty, the bony tissue at the epiphyseal plates begins rapid production. The increased rate of bone growth eventually replaces the hyaline cartilage epiphyseal plates.

• Marking the prior location of an epiphyseal plate is a unique area of bone tissue, the epiphyseal

line.

Lab Activity 11

Epiphyseal Lines

• The distal end of the femur in frontal section shows an epiphyseal line. The epiphyseal line is formed by bone production at the site where the epiphyseal plate was located.

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Appositional Growth of the

Diaphysis

Appositional growth produces an

increase in bone diameter.

Appositional Growth of the

Diaphysis

• Growth that increases the diameter, or thickness, of the bone occurs at the inner cellular (osteogenic) layer of the periosteum. • The bone diameter of the bone is increased by

osteoblasts secreting bone matrix onto existing bone.

• Osteoblast activity encircles periosteal blood vessels with matrix and forms layers of matrix (lamellae) to produce osteons (Haversian systems).

Appositional

Growth

• Sequence of appositional growth at the cellular (osteogenic) layer of the periosteum. Figure 10.45

• Observe a microscope slide preparation labeled “Decalcified Bone; cross section.”

• A cross section of the diaphysis of the developing femur (Fig. 10.46, @ 20x) shows the periosteum, compact bone of the diaphysis, medullary cavity, and bone marrow. The thin inner layer, the endosteum, is not seen at this magnification.

Figure 10.46

Lab Activity 12

Appositional Growth

Lab Activity 12

Appositional Growth

• A cross section of the diaphysis (100x) of the femur showing the detail of its wall. The diaphysis grows thicker (appositional growth) by the formation of new osteons (Haversian systems) under the fibrous layer of the periosteum.

Figure 10.47

Lab Activity 12

Appositional Growth - Endosteum

• A cross section of the diaphysis (100x) of the femur showing the detail of its wall. The diaphysis grows thicker (appositional growth) by the formation of new osteons (Haversian systems) under the periosteum. Osteoclasts of the endosteum erode the inner wall and form the medullary (marrow) cavity.

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BONE DYNAMICS

(growth, remodeling, and

maintenance)

Bone remodeling is a life long process that is necessary for the body’s skeleton to accommodate for changes mostly due to

growth, lifestyles, and aging.

Nutrients for Bone Growth,

Development, and Remodeling

• Protein

– Adequate dietary protein is required for the construction of the organic matrix, the osteoid.

• Inorganic Matrix

– The inorganic matrix requires two major components, the salts of calcium and phosphate, both of which are also of dietary origin.

Nutrients for Bone Growth,

Development, and Remodeling

• Vitamins – Vitamin C

• Vitamin C is especially important in the synthesis of collagen fibers.

– Vitamin D

• Vitamin D, of dietary origin or synthesized in the skin, is necessary for the intestinal absorption of calcium and phosphate from the intestine.

• The kidneys convert vitamin D3, cholecalficerol, to calcitriol. Calcitriol targets the intestines and promotes the absorption of calcium and phosphate.

Growth of Bone

• The growth of bones begins at about six weeks after fertilization.

• The two processes, intramembranous and endochondral ossification begin to produce bone tissue.

• As the bone tissues are produced, they are continually remodeled as to shape, internal design, and mineral content. The ages at which bones stop growing vary with the bones. However, around age 25 all of the bones have reached maturity.

• Even though the bones have reached their mature size, bone remodeling continues as surface marking and their internal framework continues to be modified throughout life.

Exercise

(mechanical stress)

• A major force in promoting bone

remodeling is exercise.

• Exercise results in mechanical stresses

that generate small electrical currents

within the bone. These small electrical

currents stimulate osteoblasts.

Exercise

(mechanical stress)

Figure 10.49

• The plates of spongy bone, the trabeculae, are position to supply the greatest structural strength. Changes if life style, such as weight lifting, change the structure of the trabeculae to accommodate for increased mechanical stress. The femur, shown in this figure, is continually remodeled to fit one’s lifestyle.

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Hormonal Regulation

Two hormones involved with tissue growth and metabolism of the body’s cells are growth hormone and thyroxine. • Growth Hormone

– Growth hormone, also called somatotropic hormone, is produced by the anterior pituitary gland. Growth hormone influences protein, carbohydrate, and lipid synthesis. Growth hormone plays a continual role in cartilage and bone growth, especially in children.

• Thyroxine

– Thyroxine is a hormone produced by the thyroid gland that regulates cell metabolism, especially involving proteins and carbohydrates.

• The coordinated effects of both hormones are necessary to produce normal skeletal growth and maturation.

Hormonal Regulation

• Additionally, two hormones that directly affect bone are calcitonin and parathyroid hormone. • The hormones, parathyroid hormone and

calcitonin, are involved in the maintenance of

blood calcium levels; thus, directly influencing

the homeostasis of the skeleton. Bone may be demineralized when the body needs calcium or mineralized when calcium supplies are plentiful.

Lab Activity 13

Hormonal Regulation

• Observe a slide preparation labeled “Thyroid and Parathyroid glands,” or “Thyroid gland,” and “Parathyroid gland.” Figure 10.50

Calcitonin – Parafollicular Cells

• The parafollicular cells of the thyroid produce calcitonin. • Calcitonin is released when blood ionic calcium levels

increase.

• The primary function of calcitonin is to decrease the blood’s level of ionic calcium when blood ionic calcium levels are high.

• Calcitonin targets:

– (1) osteoblasts which promote the deposition of calcium into bone matrix, and the

– (2) kidneys to increase excretion of calcium in the urine. Intestinal absorption of calcium is low due to a low level of parathyroid hormone.

Calcitonin

• The function of the thyroid hormone, calcitonin, in regulation of blood ionic calcium. Figure 10.51

Parathyroid Hormone

• (PTH) is released when blood ionic calcium levels decline.

• Its primary function is to increase the blood’s level of ionic calcium.

• Parathyroid hormone targets:

– (1) osteoclasts to increase the destruction of bone matrix,

– (2) the intestines to increase absorption of calcium and phosphate ions,

– (3) the kidneys to increase reabsorption of calcium and to increase the production of calcitriol to additionally promote intestinal absorption of calcium.

(18)

Parathyroid Hormone

• The function of parathyroid hormone in regulation of blood ionic calcium. Figure 10.52

Lab Activity 14

-Bone Remodeling

• Observe a slide preparation labeled “Ground Bone; cross section.”

Bone remodeling involves the processes of

– (1) reabsorption and – (2) deposit.

• Bone remodeling occurs at the cellular layer of the periosteum and at the endosteum.

Figure 10.53

Lab Activity 14

-Bone Remodeling

• Bone remodeling produced the repair of the fractured leg bones, the tibia and fibula.

Figure

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References

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