|THE SKELETAL SYSTEM
The skeletal system includes all the bones of the body plus the joints where they attach to each other.
The bones of the lower extremities or legs are connected to the axial skeleton via the pelvic girdle which is formed by the two hip bones. It protects the bladder, reproductive organs, lower colon and rectum. In the male the pubic arch of the pelvis is less than 90 degrees wide. In the female, it is greater than 90 degrees. This difference in width is necessary for the female pelvis to perform child birth.
The longest, strongest and heaviest bone of the body is the femur, commonly called the thigh bone. At one end it is connected to the pelvis an at the other end to the lower leg, which is made out of the tibia or shin bone and fibula. The tibia bears all of our body’s weight, the fibula bears no weight at all. The patella or knee cap is a large bone between the femur and fibula. It protects the knee joint and tendons that form the knee.
The bones of the ankle and foot must carry all of our body weight as we walk, stand or run. And the 26 bones and 33 joints that make up our ankle and foot enable it to do just that.
The skeletal system is divided into two divisions: the axial skeleton and the appendicular skeleton.
The axial skeleton includes 80 bones; comprising the skull, vertebral column and thorax.
The appendicular skeleton consists of the bones of the shoulders, upper extremities, hips and lower extremities.
The skeletal system is made out of 206 different bones which come in four basic shapes:
Long bones such as
Short bones like
Flat bones such as
Irregular bones like
There are two types of bone tissue:
Compact bone which is dense, smooth and very strong and cancellous bone which is spongy and light weighted. Both types of bone tissue contain living cells which help to make repairs when the bone is injured or broken.
The bones of the upper extremities or arms are connected to the axial skeleton via the shoulder girdle. This consists of the scapula or shoulder blade and the clavicle or collar bone. The arm itself is composed of the humerus or upper arm and the radius and ulna of the forearm plus the wrist and hand; which consists of 27 separate bones. Because of this large number of small bones our hands are capable of more movement than any other part of our body.
The entire skeleton system of and average adult weighs less than 10 kg. If you attempted to replace this with a steel skeleton that was just as strong, it would weigh 400 hundred kg and still don’t have the resilience of bone or the ability to repair itself. Harder than reinforced concrete, lighter than stainless steel, able to repair itself, bone is the perfect material to provide the framework for the human body
Our skeleton protects our internal organs, provides a framework o scaffolding that allows us to stay upright and move.
Stores minerals that our body needs to function properly. Produces blood cells.
Without the protection of our skeleton, even a simple bump on the head or chest could injure vital internal organs.
A typical long bone has a main shaft called the diaphysis, composed of compact bone, and two ends called epiphyses composed of cancellous bone. The main shaft is covered with a membrane of living cells called periosteum to which muscles and tendons attach themselves.
Inside the main shaft is a cavity called the medullary cavity, which contains bone marrow. Bone marrow stores fat; produces blood cells and plays an important part in our body’s immune system.