Actions & Processes of the Skeletal System

Instructor: Amanda Robb

Amanda holds a Masters in Science from Tufts Medical School in Cellular and Molecular Physiology. She has taught high school Biology and Physics for 8 years.

Although you may think of your skeleton as just a scaffold for your body, today you'll be learning about many other important functions of the skeleton. From creating muscle movement to developing your immune system and cells in the cardiovascular system, the skeleton is far more than just a sturdy frame.

What Is the Skeletal System?

Ouch! A baseball comes flying at you and cracks right into your arm. Your arm swells like a balloon and sure enough at the hospital, the doctor says you have a broken bone. Bones seem so solid, so how could this happen? More amazingly, the doctor says he'll apply a cast and in a few months your bones will be good as new. Although maybe you never really considered it, bones must be alive, since they are part of the skeletal system, a collect of tissues, and cells that support your body.

Human skeleton

Beyond keeping your limbs straight when they are intact, bones have a range of other functions in the body. Today, we'll learn about the more commonly known functions, like structure, protection and movement, as well as lesser known functions, like hematopoieisis and mineral homeostasis.

Protection and Support

The skeletal system is essential for protecting the soft tissue in your body. Bone is made of bone cells called osteocytes. Osteocytes are responsible for maintaining healthy bones. They secrete proteins that create a flexible matrix around the bone cells, allowing for some stretch in the tissue. The hardness of bone comes from deposits of calcium and phosphate which form mineral crystals, creating the hard, white appearance we recognize as bone.

Cross section of bone

All these parts work together to form a hard skeleton for protection. For example, when you ride your bike you wear an extra layer of protection, a helmet. This reinforces the hard bone of your skull that protects your brain. Your ribs, although flexible, similarly protect your lungs from being punctured.

Other bones, like the long bones in your legs and arms, give your body the support needed for upright locomotion, a unique feature of humans compared to other primates.


The skeletal system is crucial for any muscle movement. Skeletal muscle, a type of voluntary muscle in our body, is attached to bone by tendons. Go ahead and flex your bicep, showing off your muscles. The bicep muscle is attached to bones in the shoulder and your elbow at the other end. When you contract the bicep, the muscle shortens. Since it's attach to a bone at each end, the contraction pulls your lower arm up as the muscle shortens.

Tendons attach the bicep muscle to the skeleton for traction

This goes for all the muscles in your body, including the large ones in your legs, like the hamstrings and quadriceps that allow you to walk and run.


Bone isn't all about being sturdy though! Deep inside the calcium matrix of bone is a spongy part called the bone marrow. Bone marrow contains stem cells, or cells that can become other types of cells. These hematopoietic stem cells divide into any type of blood cell. They make all white blood cells for your immune system, your red blood cells, and platelets for blood clotting. This process, called hematopoiesis, is especially unique since normally, cells divide to make more of themselves, like cells in your lungs. However, all the blood cells in your whole body come from the bone marrow.

Hematopoiesis creates all types of blood cells from one stem cell
blood cells

Sometimes people get bone marrow cancer, called leukemia. In leukemia, the stem cells are damaged and don't make proper blood cells. The blood cells are cancerous and no longer do their job, dividing out of control. They can also spread to the rest of the body.

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