The main differences between compact bone and spongy bone are their structures and the way each functions. Both types of bone tissues are necessary for movement of the body and support of the skeletal system.
Compact bone, sometimes referred to as cortical bone, is the outer shaft of bone that supports and protects the body. This is the visible part of a skeleton. But, there's much more on the inside. It contains structural units known as osteons that run parallel to the bone. This type of bone tissue stores calcium, which is an important mineral that in turn hardens and strengthens the bone. The body's skeletal weight is comprised of 80 percent of compact bone, so it's the heaviest part. This amazingly strong bone tissue can support up to 5,000 pounds of weight.
Compact bone is responsible for forming major components of long bones like the arms and legs. Yellow bone marrow is kept in the compact bone cavity, which actually stores fat. The fat is what gives it the yellow color. Thin membranes known as lamellae don't have space in between them in the compact bone tissue. Yet little pathways of blood vessels and nerves fit in the structure and run through the tissue to make repairs as needed.
Spongy bone, oftentimes referred to as the cancellous bone, is the soft and porous bone tissue situated in the inner part of the bone. It contains thin rods and plates of tissue, known as trabeculae, that sort of branch out. The spongy tissue stores red bone marrow between the lamellae, where it also has some spacing, unlike the compact bone tissue. This red bone marrow, also known as myeloid tissue, produces vital red and white blood cells. When babies are born their bodies have red bone marrow and develop the yellow as they mature. Adults typically have half red and half yellow.
The spongy bone tissue is responsible for 20 percent of the body's skeletal weight. This type of tissue is crucial for helping to formulate elements of the short bones in the body like the ankles and wrists. It is not heavy weight-bearing and has a low calcium level. If this tissue doesn't get an adequate supply of calcium, it can weaken, making it prone to breakage. This is a part of the bone structure that is susceptible to diseases like osteoporosis.
How the Two Work Together
Compact and spongy bones do work together despite their differences. And they have a few similarities. Both of these bone tissues exist in humans and animals. Both are comprised of connective tissues that form the bones. Compact bones have more calcium than spongy, but they both contain levels of calcium essential for bone health. Along with the assistance of the muscular system, the support of the compact and spongy bones helps the body to move. The spongy bones serve as a sort of shock absorber or cushion for the rigid compact bones. Compact and spongy bones are two kinds of bone tissue that work together to make up most of the body's bones. The only exception to this is the vertebrae that form the backbone that protects the spinal cord.