Everyone Has a Skeleton in the Closet
SKELETAL SYSTEM
The bones of the body are the structural architecture that gives the human body its distinctive shape. Without the skeletal system, you wouldn’t be able to do much of anything. You would be a big pile of soft tissue, unable even to sit on the couch and be a couch potato. However, bones do much more than maintain your physical shape and help your body to do work. Bones not only partner with muscles to move body parts; they also help with new blood cell formation as well as act as a storage compartment for calcium.
Levers for Movement
If you have ever used a crowbar, you have demonstrated the concept of how levers work. Many bones in the skeletal system act as levers for the body, while the skeletal muscles (named such for their attachment to bones) provide the power for the work to be completed. Therefore, just like a lever system, the points where the skeletal muscles attach to the bones and which bones the muscles are attached to dictate the power and strength required to accomplish a task.
Skeletal muscles contract and pull in a straight line. One attachment is relatively fixed whereas the opposite attachment point is movable. The biceps muscle, for instance, has a relatively fixed attachment point (or origin of the muscle) at the scapula on the shoulder. At the opposite end of the biceps, the movable attachment point (or insertion of the muscle) is to the radius bone of the forearm. When the muscle contracts, it pulls on both ends, attempting to shorten the muscle toward the middle. However, because the shoulder is fixed, the only appreciable movement that can occur is for the forearm to be pulled closer toward the shoulder (flexing of the forearm). This action of the muscle, which is driven by the muscle contraction, is in fact a result of the involvement of the bones of the skeletal system.
Hematopoiesis
After just a few weeks following conception, the developing embryo (the unborn offspring from the time of fertilization to the end of the eighth week of gestation) will have grown too large for oxygen to diffuse to all the cells of the body. Red blood cells are formed from embryonic precursors and a primitive circulatory system is established. As the embryo grows and becomes a fetus (the unborn offspring from the ninth week through birth), the spleen and the liver serve as the location for new red blood cell formation. However, these organs serve other functions for the adult human. In adults, the blood cell production duties are contained in the long bones of the arms and legs.
Hematopoiesis is the production of blood cells from embryonic stem cells present in the bone marrow of the long bones. Bone marrow is the fatty substance in the bone cavity that helps produce blood cells. Erythropoiesis is the specific production of red blood cells, while leukopoiesis is the production of white blood cells.
Anatomy of a Word
erythropoietin
Erythropoietin (EPO) is a hormone produced by the pituitary gland that increases the rate of red blood cell production. This increase can be directly stimulated by living in an area that has a low atmospheric oxygen content, such as places with a high altitude.
Calcium Storage
Bone is principally composed of a hard, inorganic calcium phosphate matrix. While this gives bones the strength to resist gravity and support the movements of the body, it also gives the body a great reservoir of calcium. Unlike enamel, the calcium phosphate matrix of the teeth, bone is porous and filled with living cells that can repair bone.
Anatomy of a Word
osteoporosis
Osteoporosis is a disease of the elderly, particularly females, in which calcium and bone matrix is progressively lost. This eventually weakens the bones, making them more brittle and prone to breaking.
Just as sugar levels in the blood are regulated by two hormones (insulin decreases blood sugar and glucagon increases blood sugar), calcium is also closely monitored and regulated by two hormones. Parathyroid hormone functions to increase blood calcium levels while calcitonin decreases blood calcium levels.