Bones Archives - Eva Varga

The bones in the human body make up the Skeletal System.  Bones serve several purposes. In addition to giving the body structure, they protect important body parts. For example, the skull protects the brain. The tissue inside bones, the bone marrow, makes blood cells and stores fat. Also, bones house nerves and work with the muscles to help us move.

We likely all know what a bone looks like from the outside. But what do they look like on the inside?  For this lab, I thought something new and fun would be to dissect a bone.

From a local butcher, I obtained a bovine leg cut down the center to see the bone interior lengthwise. With a class of students, I would also suggest about 15 discs or cross-sections (about 1″ thick) for students to dissect and observe under the dissecting microscope. I, sadly, neglected to do this.

I had the students identify the following structures:

• Femur shaft, head, and trochanter
• Articular cartilage
• Compact bone
• Spongy bone
• Red and yellow marrow

We were also able to locate and identify skeletal muscle, tendon, and blood vessels.

Anatomy of Bones

Bones are complex structures and they differ from species to species and by location in the body. The differences are mostly in the function of the bone, but there are some things that most bones have in common.

We often think that a bone is a solid structure. However, some parts of the bone are hard while other parts are very soft. Parts will look very different when examined closely – with a magnifying lens or microscope.

The bones in your legs, and in the legs of a cow, are made of both compact bone and spongy bone.  The exteriors are walls of calcium and other minerals. This compact bone runs the length of the bone and is designed to bear loads and protect organs. The larger the animal, the thicker the compact bone. There are small channels running through the calcium to carry blood and nerves to and from the marrow, but in general, the compact bone is not very porous.

The marrows of bones are complex yet can be broadly divided in two categories, red spongy marrow and yellow marrow. At the ends of bones, you find highly porous marrow, also called red spongy marrow. Spongy marrow serves as a home to stem cells that produce blood cells. Red spongy marrow is the hard honeycomb marrow that you have likely seen in some cuts of steak because the bones are often cut open by a bandsaw. Yellow marrow is the type you find in the center of femurs and other leg bones. It is mostly fat but is edible.

The entire bone is covered by a thin covering called the periosteum, which contains blood vessels, nerves, and bone-forming cells. 

Each end of the bone is covered with a cap made of cartilage.  The cartilage covers the part of the bone where there is a joint or place where two or more bones come together. The cartilage is white in color, is slippery and smooth, and enables bones to move without rubbing together.