The skeletal system works to support your body. Without your skeletal frame, you would be unable to move. Humans are vertebrates, meaning we have bony, articulated (jointed) endoskeletons. An endoskeleton is a frame within the body that offers support as it grows and develops. The skeletal system offers protection, support, blood cell formation, stores minerals and energy and aids movement.
Bones are made of connective tissue. Connective tissue is found all over your body and comes in different forms. Bones are mostly made up of collagen fibrils. Their surfaces are covered with special cells made of calcium compounds. This is what gives the bones their structure and strength.
Inside the bones, there are cells that contain fibers and ground substance. If you were to look at bone cells under a microscope, you would find tiny grains scattered throughout. As the cells develop, the calcium compounds inside crystallize. This creates bones as we know them: able to withstand great pressure and strength without breaking. Calcium and phosphorus are stored within your bones.
An interesting fact about the skeletal system is that in spite of its strength and ability to support, the tissue within bones is very light. Our skeletons comprise only about 18 percent of our body weight.
A human adult has a total of two hundred and six bones. Bones are considered to be living organs because they are made up of nerve, muscle and epithelial tissue, as well the connective tissue that binds everything together. If you were to look at the cross section of a long bone, such as your femur, you would see a shaft in the middle that is hollow. This central cavity contains either red or yellow marrow. Red is newly produced marrow. As bones age, the red marrow converts into yellow. This special, yellow marrow is an energy source.
Within the bones, red and white blood cells are produced, along with platelets. There is a fibrous sheath called a periosteum that contains blood vessels which supply oxygen and nutrients to the bone tissues. Blood vessels get in and out of the bones by little openings called nutrient canals.
As we develop, our bones grow with us. Hyaline cartilage produces lateral growth, which is later replaced by bone tissue. The bones add surface area through appositional growth, which causes your bones to widen. The periosteum is responsible for secreting new bone tissue.
The skeletal system is covered with muscles that enable us to move. These muscles are attached to the bones through tendons and often stretch from one end of the bone to the other. Your bones and muscles work together through a series of impulses and signals communicated between the brain and skeletal muscles. In order to move, the nervous system signals a skeletal muscle to contract. When the muscle contracts, this movement causes the attached bone (or bones) to follow.