Anatomy of a Long Bone Help

By — McGraw-Hill Professional
Updated on Aug 30, 2011

Introduction to the Long Bone

To fully understand the skeleton, we must examine the anatomy of a typical long bone. A long bone is simply a bone that is much longer than it is wide. Consider, for instance, the “thigh” bone or femur ( FEE -mur). As Figure 13.5 reveals, the femur has a main shaft, called the diaphysis (die- AH -fuh- sis ), which is literally a “growth” (phys) “through” (dia-) the middle of the bone. And capping each end of the diaphysis (main bone shaft) is an epiphysis (eh- PIH -fih- sis ) – a “growth” (phys) present “upon” (epi-) the shaft.

Skins and Skeletons Anatomy of a Long Bone

Fig. 13.5 General anatomy of a long bone.

Bone Matrix and Medullary

Most of the long bone is composed of dense or compact bone matrix ( MAY -tricks). This is the white, rock-hard, calcium-rich portion of the long bone. But in the “middle” (medull) portion of the long bone, we find the medullary ( MED -you- lair -ee) or marrow cavity. This medullary (marrow) cavity, as its name indicates, contains the yellow bone marrow. The yellow color of this type of marrow is mainly due to the presence of adipose ( AH -dih- pohs ) or “fatty” connective tissue.

Cancellous Bone (Spongy Bone)

Finally, we see the spongy or cancellous ( CAN -seh- lus ) bone located within each epiphysis of the long bone. It obviously gets its spongy name from the existence of numerous holes and an extensive network of cancelli (can- SEL -eye) – “little crossbars” (cancell) of hard bone matrix. Much like a real sponge, therefore, spongy (cancellous) bone tissue consists of a network of cancelli or little crossbars and the many holes between them. Unlike a real sponge, however, spongy bone tissue contains red bone marrow within its holes. The red bone marrow is red in color mainly due to the fact that it consists of many blood vessels. These dozens of blood vessels run and branch extensively throughout the holes of the spongy bone. Their main function is that of hematopoiesis ( he -muh-toh-poi- E -sis) – the process of “blood” ( hemat ) “formation” (- poiesis ). Most of the blood cells (and blood cell fragments) ultimately are formed by hematopoiesis occurring within the red bone marrow. The blood cells enter the general bloodstream when they are circulated out of the long bone, through the vessels leaving the red bone marrow.

Practice problems for these concepts can be found at:  Skins And Skeletons Test

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