Osseous Tissue

In chapter five you were introduced to osseous or bone tissue. There are two kinds of bone, compact and cancellous. These two types occupy different regions of bones, have different functions, and are histologically distinct.

Compact osseous tissue makes up the strong outer portion of bones. This type of bone is composed of tightly packed cylindrical structures called osteons (osteon = Gr. bone). Each osteon is composed of concentric rings of mineral called lamellae surrounding a central canal. Within the lamellae are lacunae containing the bone cells (osteocytes). The lacunae are connected to one another by small channels called canaliculi. Cytoplasmic extensions of osteocytes fill the canaliculi allowing diffusion of nutrients and wastes from one osteocyte to another and eventually to the blood vessels in the central canal. Central canals of adjoining osteons are connected by perforating canals which also contain blood vessels.

Cancellous tissue is found within bones and is the site of blood cell production. Cancellous bone is a spongy structure composed of overlapping plates of matrix called trabeculae. Blood is formed within the spaces between trabeculae.

Covering the outside of the bone is a collagenous sheath, the periosteum (peri = Gr. around), which is held to the bone by Sharpey's fibers. These fibers are extensions of the collagen fibers of the periosteum. The Sharpey's fibers extend into the matrix of the osteons.

Exercise 7.1

Correctly label Figure 7.1 using the terms at the bottom. Use your textbook to help you identify the various parts.

Figure 7.1 Osseous Tissue

Blood vessel Canaliculus Cahcellous bone Central canal Lacuna Lamella Osteocyte Osteon Perforating canal Periosteum Sharpey's fiber Trabeculae

1. How is an osteocyte different from a chondrocyte (see chapter five)?

2. Osteocytes are enclosed within lacunae. Most osteocytes do not have a direct blood supply. How do these distant osteocytes acquire nutrients and rid themselves of waste?

3. What is the name of the concentric rings which make up an osteon?

4. How are osteons held together?

5. What is another name for an osteon?

6. What structures can be found within the central canal of an osteon?

7. Anatomically speaking, how is a central canal different from a transverse canal?

8. What is the name of the collagenous connective tissue which covers the outer surfaces of bones?

9. How is this connective tissue held onto the bone?

10. What is the name of the bony matrix structures within cancellous bone?

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