Macroscopic structure of bone Diagram of the outside of a long bone:

Figure 6.01 Parts of a Long Bone ©2004 John Wiley & Sons, Inc. All rights reserved.

Diaphysis – (die-AF-i-sis) main middle portion of the bone Epiphyses – (e-PIF-i-seez) distal and proximal ends of the bone

Metaphyses – (me-TAF-i-seez) region in a mature bone where the diaphysis meets the epiphysis Epiphyseal (e-pi-FIZ-ee-al) plate – a layer of cartilage in growing bone where the diaphysis can grow in length Epiphyseal line – a bony structure that replaces the epiphyseal plate when the bone is no longer growing

Articular cartilage – thin layer of cartilage over the epiphysis where the bone connects with another bone. Cushions and protects the ends of the bone. Has limited ability to repair damage to it.

Periosteum (per-ee-OS-tee–um) dense irregular connective tissue that surrounds the parts of the bone that do not have articular cartilage. Contains cells that enable the bone to grow wider and thicker, but not longer.

Chew… Draw a long bone cut lengthwise. Label the diaphysis, epiphysis, metaphysis, epiphyseal plate/line, articular cartilage and periosteum.

Protects the bone Assists in fracture repair Helps nourish bone tissue Attachment point for ligaments and tendons

Inside of a long bone:

Figure 6.01 Parts of a Long Bone ©2004 John Wiley & Sons, Inc. All rights reserved.

Medullary (MED-you-larry)cavity – space inside the diaphysis that contains yellow bone marrow in adults. Endosteum (end-OS-tee-um) – membrane lining the inside of the medullary cavity. Contains a single layer of bone-forming cells.

Compact bone – dense bone for protection and support Spongy bone – looks like a network of bone with marrow in between

Microscopic structure of bone Bone is a connective tissue Matrix: 50% crystallized mineral salts to provide hardness 25% collagen fibers to provide some flexibility 25% water

Cells – 3 kinds Osteoblasts – bone building cells which produce the matrix Osteocytes – mature bone cells Develop from osteoblasts Maintain metabolism of bone – take in nutrients and release wastes into blood

3 kinds of bone cells continued Osteoclasts – huge cells created by the fusion of 50+ monocytes (white blood cells) Produce lysosomal enzymes and acids to break down bone matrix (called resorption)

Compact bone tissue Contains few spaces between the cells and matrix Arranged in units called Haversian systems or osteons.

Figure 6.02a Histology of Bone ©2004 John Wiley & Sons, Inc. All rights reserved.

Parts of a Haversian system Haversian canal – a central canal in the osteon Contains blood vessels, lymphatic vessels and nerves Connects to perforating (Volkmann’s) canals which lead into the bone from the periosteum.

More parts of a Haversian system Concentric lamellae – rings of hard, calcified matrix around the Haversian canal Lacunae – small spaces between the lamellae which contain osteocytes

More parts of a Haversian system Canaliculi – small channels filled with extracellular fluid which connect the lacunae with each other and the central canal Canals provide a route for diffusion of oxygen, nutrients and wastes since diffusion through lamellae is very slow

Figure 6.02a Histology of Bone ©2004 John Wiley & Sons, Inc. All rights reserved.

Spongy bone tissue features Does not contain osteons Has trabeculae which is a network of thin columns of bone Contains spaces between the trabeculae filled with red bone marrow

More spongy bone features Osteocytes in lacunae lie within the lamellae. Canaliculi radiate out from the lacunae

Figure 6.02b-c Histology of Bone ©2004 John Wiley & Sons, Inc. All rights reserved.

Differences between spongy and compact bone Spongy bone makes up the epiphyses of long bones and makes up most of the flat, short and irregular bones Compact bone is found in the diaphysis of long bones

Figure 6.01 Parts of a Long Bone ©2004 John Wiley & Sons, Inc. All rights reserved.

More differences between spongy and compact bone Spongy bone is lighter than compact bone Spongy bone is the only site of hemopoiesis in adults

Pictures used by permission from Introduction to the Human Body, 6th edition by Tortora and Grabowski. Published by Wiley Publishing.