Bone

 


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A. Woven Bone       Woven bone is the first bone formed in the embryo, where it is gradually replaced by lamellar bone, except in a few places where woven bone persists. These include the places where tendons insert into bones and the tooth sockets. In woven bone the bundles of collagen fibers of the bone matrix are organized in a meshwork, similar to dense irregular connective tissue. Woven bone can be identified microscopically by looking for lacunae that are not arranged in parallel rows and by stopping down the condenser diaphragm and looking for the absence of lamellae and a woven pattern of collagen fibers. Look for woven bone in areas of newly formed bone and where tendons attach to the bone.

 

 

 

 

 

 

 

 

 

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1,2

15b

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19

 

Developing bone, decalcified preparation, H&E.

 

 

Tendon inserts, decalcified bone preparation, H&E.

 

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B. Lamellar Bone       Lamellar bone is the mature form of bone in which the bundles of collagen fibers in the bone matrix are organized into successive sheets or lamellae in which all of the bundles are oriented in the same direction, much like dense regular connective tissue. Lamellar bone can be identified microscopically by lacunae arranged in parallel rows and fine parallel lines, seen best with the condenser stopped down, that mark the boundaries between adjacent lamellae.
1. Dense (compact)

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1-3

suppl.
Bone, ground preparation, x.s., stained with India ink. These images demonstrate the effects of using the condenser lens diaphragm to vary contrast.
Bone, ground preparation, x.s., Stained with India ink. Note the lacunae and canaliculi. The lamellae of matrix of the Haversian systems are best seen by stopping down the condenser diaphragm.

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Bone, decalcified preparation, H&E.

suppl.
Bone, decalcified preparation, H&E.
Periosteum and Sharpey's fibers. Bone, decalcified preparation, H&E.
2. Spongy (cancellous)

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2,3

15

suppl.

Bone trabeculae in the marrow cavity of a long bone, decalcified preparation, H&E. Although Figs. 2 & 3 in the Atlas are from compact (dense) bone, similar developing Haversian systems can be seen in the larger trabeculae of cancellous (spongy) bone. Stop down the condenser diaphragm and look for the lamellae of bone matrix that are characteristic of lamellar bone.
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C. Cells of Bone

1. Osteocytes

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Osteocytes are always located in lacunae. They are often shrunken away from the wall of the lacuna and only the nucleus is typically visible.
2. Osteoblasts
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Osteoblasts are located on the surface of bone and indicate that new bone matrix is being formed.
3. Osteoclasts
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Osteoclasts are located on the surface of bone and indicate that bone matrix is being digested and resorbed. The depression in the bone surface that they make while digesting the bone matrix is called a Howship's lacuna.
D. Bone Formation
1. Endochondral

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1-3
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18a

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Endochondral bone formation, decalcified. In H&E the cartilage matrix stains light purple, calcified cartilage stains dark purple and bone matrix stains pink. All of the stages shown in the Atlas may not be present on your slide. In addition to the details outlined in the Atlas note the vasculature of the marrow cavity and the free cells of marrow proper. Look for fragments of calcified cartilage covered by woven bone (primary bone), and areas of woven bone covered by lamellar bone (secondary bone).

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All samples are decalcified. On slide 10 (pubic symphysis) you may be able to find a reduced epiphysial plate. A regular plate similar to Fig. 1 may not be present in all slides of endochondral bone formation.
2. Intramembranous

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16a

16b

16c

Frontal section through the head of a rodent embryo, showing developing skull bones, including upper jaw with teeth. Note cartilage of the nasal septum. Al samples are decalcified. Mallory's triple stain (16a), H&E (16b) and iron hematoxylin (16c).




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