Human skeletal system: Structure and functions

Did you know that the adult human skeletal system contains 206 bones? The human skeleton provides the body with a multifunctional structure. It also consists of the joints, cartilage, tendons, and ligaments that connect them.

Skeletal system functions

The main functions of the skeletal system are:

  • Support for the body
  • Movement
  • Protect internal organs
  • Blood cell production
  • Storage of minerals, particularly calcium
  • Growth and development

The human skeletal system is divided into two main parts:

The axial skeleton forms the central axis of the human body and is composed of 80 bones that include the bones of the skull, the ossicles of the middle ear, the hyoid bone of the throat, the vertebral column, and the thoracic cage. It also provides protection and support for the brain, spinal cord, and vital organs and a surface for muscles to attach.

The appendicular skeleton supports the appendages. It consists of 126 bones that include both the upper and lower limbs, feet, ankles, shoulders, and pelvis.

Components of the skeletal system

The skeletal system is composed of four main types of connective tissue:

Bone: A rigid form of connective tissue that is part of the skeletal system of vertebrates and is composed principally of calcium.

Ligament: A small band of dense, white, fibrous elastic tissue that connects the ends of bones together form a joint or assists in holding organs in place.

Tendon: A tough, flexible and inelastic band of fibrous connective tissue that connects muscles to bones.

Joint: Joints hold the bones of the skeleton together and support movement. They can be grouped together by function and structure, such as ball-and-socket, hinge, and pivot joints.

Types of bones

There are five types of bones in the human skeletal system: long, short, flat, irregular, and sesamoid.

Long bone: Helps to facilitate movement and support the weight of the body. Long bones are characterized by a long tubular shaft and an articular surface at each end of the bone where ligaments and tendons attach. These bones include the major bones of the arms and legs such as the humerus and femur, tibia and fibula, and the radius and ulna.

Short bone: Helps to provide stability and movement within the ankle and wrist joints. They provide little to no movement. Short bones are roughly cube-shaped and are as long as they are wide. Examples of this type of bone include the carpals and metacarpals in the wrists and ankles.

Flat bone: The primary purpose of this type of bone is to protect internal organs such as the brain, heart and lungs. It also provides a large surface area for muscles to attach to. Examples of this type of bone include the cranium (skull), the thoracic cage (sternum and ribs) and the ilium (pelvis).

Sesamoid bone: The function of this bone is to protect tendons and diminish friction and wear on joint surfaces. This type of bone is usually small and round and is found in the hands, feet, and knees. A common example of a sesamoid bone is the patella (kneecap).

Irregular bone: Basically, if it’s not listed above, it’s an irregular bone. These types of bones vary in size and structure and the shape may be complex. Irregular bones serve different functions depending on location. For example, vertebrae protect the spinal cord and the hyoid bone maintains tracheal and pharyngeal support.

knee diagram

See page for author [Public domain],Mikael Häggström via Wikimedia Commons

When you consider the relationship between the axial and appendicular skeleton and the soft tissues of the body, it becomes clear that the primary functions of the skeleton are support, protection, and motion. Of these functions, support is the oldest and most primitive. Similarly, the axial skeleton was the first to evolve.

A distinguishing characteristic of the human skeleton in comparison to other mammals is erect posture. Our bodies are, to some extent, similar to a tall building with legs. Enormous advantages have been gained from this type of posture, with the most prevalent being that our arms and hands can be used for other functions.

Different types of joints

What are the different types of joints by function?

Joints are crucial structures throughout the entire body. There are several different types of joints, including:

Synarthrosis: These immovable and strong joints include skull sutures, the articulations between the teeth and the mandible, and the joint found between the first pair of ribs and the sternum.

immobile or virtually immobile suture joints of the human skull from BC Open Textbooks

Synarthrosis, or, basically immobile joints.

Amphiarthrosis: These joints allow slight movement and include the distal joint between the tibia and the fibula and the pubic symphysis of the pelvic girdle.

limited mobility human intervertebral disc joint from  BC Open Textbooks

Amphiarthrosis, or, limited mobility joint.

Diarthrosis: These joints allow full movement and include many bone articulations in the upper and lower limbs. Examples of these include the elbow, shoulder, and ankle.

freely moving human hip joint from  BC Open Textbooks

Diarthrosis, or, freely moving joint.

What are the different types of joints by structure?

The different types of joints in the human body can be described related to structure.

Fibrous: Thick connective tissues composed of collagen fibers found between the articulations of fibrous joints.

fibrous joint of human skull

Fibrous joint connecting bones of the human skull. OpenStax College [CC BY 3.0], via Wikimedia Commons

Cartilaginous: Joints that join bones with cartilage.

Cartilaginous joints

Cartilaginous joints. OpenStax College [CC BY 3.0], via Wikimedia Commons

Synovial: These are characterized by the presence of an articular capsule between the two joined bones. Bone surfaces at synovial joints are protected by a coating of articular cartilage.

examples of synovial joints

Synovial joints. OpenStax College [CC BY 3.0], via Wikimedia Commons


Watch some of the amazing things our skeletal system allows humans to do!


This page was written by on Oct 4, 2016.
This page was last reviewed and updated by on Jul 23, 2022.