Structure and Function of the Skeletal System Lesson

What if the human organism did not have a skeletal structure? Life as a human would amount to that of a slimy blob that oozed from place to place and struggled to survive. Just think: Could the lungs expand with the weight of the body sitting on top? Of course not!

Let's examine our previous knowledge of the skeletal system.

Skeletal System
Bones are....	the hardest and most enduring of all human tissue
Bones grow..	continually from birth till our mid 20's
If broken, bones will...	re-grow and repair themselves
Calcium is..	important for strong healthy bones
The skeleton is made up of...	around 300 bones (give or take)

All Bones Are Not the Same

The human skeletal system is composed of bones varying in size and shape. Bones are classified based on their shapes. Let's take a closer look at the shape classifications.

Classification of Bones by Shape, full description below image

See description of image Links to an external site.

Long bones - forearm and thigh

Short bones - cube like appearance (wrist, ankle)

Flat bones - broad plate like structures (skull, ribs)

Irregular bones - vary in shape and size often connecting other bones (vertebrae, facial bones)

Sesamoid bones - round bones imbedded in tendons adjacent to joints (patella)

Long Bones

Diagram of a Longbone, full description linked below

See description of image Links to an external site.

Bone Structure & Function
Bone Structure		Function
Periosteum	Vascular membrane	Helps form and repair bone tissue
Osteocyte	Bone cells	Form bone tissue Transport nutrients and waste
Compact bone Cortical bone	Tightly packed tissue matrix Forms the hard exterior of bones	Supports body tissues Protects organs Stores minerals
Spongy bone Cancellous bone	Less dense and softer tissue matrix found on the ends of long bones Highly vascular Much lighter than compact bone tissue	Metabolic activity includes the exchange of calcium ions and production of red blood cells
Medullary cavity	The hollow chamber inside the diaphysis of the bone	Endosteum Bone forming cells Soft connective tissue

Watch the video below to learn more about the Microscopic Structure of Bones.

Short Bones

Short bones are as wide as they are long. Short bones provide support and stability with little or no movement. These bones lack the long axis that is found in long bones.

Notice that the bones of the wrist are irregularly shaped.

Bone Formation and Development

Initial bone formation begins during the first weeks of prenatal development. These bony structures continue the process of growth and development into adulthood. Human bones are classified as endochondral or intramembranous bones. The structural integrity of the bone is maintained through remodeling. Bone remodeling involves the removal of mature bone and replacement with new bone tissue.

Two types of bone cells: osteoclasts, which remove mature bone tissue, and osteoblasts, which form new bone tissue.

Intramembraneous bone development begins during the initial weeks of fetal development. Flat, broad bones of the skull develop and are remodeled in a process termed intramembranous ossification. During this process, sheet-like layers of connective tissue aggregate together to form the specialized protective tissue of the brain. This aggregation results in soft tissue with an overlay of osteoblasts functioning as a protective structure for the newly developed brain. The bone remodeling process strengthens the protective mechanism of the skull over time and eventually forms a hard boney shell protecting the brain of the human organism.

The majority of the bones of the body are endochondral bones. These bones develop from masses of cartilage that are shaped like the future bone.

Diagram of bone growth, full description below image

See description of image Links to an external site.

A growing long bone compared to a mature long bone, full description linked below

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Bone remodeling of this bone is termed endochondral ossification.

This process involves the development of the bone from the ends of long bones, below the epiphyseal plate, leading to a longer diaphysis. For that reason, the epiphyseal plate is often called the growth plate.

Two Skeletons - One Purpose

The human skull possesses four pairs of hollow cavities known as sinus cavities. Many human beings are painfully aware of these cavities during the spring and fall seasons. The sinus cavities functions include:

Mucus production moistens the air entering the nose
Lightening the bones of the skull
Resonating chambers to accentuate speech

Illustration of a woman's face and a human skull with highlighted sinus regions.

Use the activity below to test your knowledge of bone shapes.

IMAGES CREATED BY GAVS OR OPENSOURCE