Human Skeletal System: Parts, Functions & Diseases Explained

The human skeletal system, or simply the skeletal system, forms the internal framework of the body. It is made up of bones along with supporting structures such as cartilage, tendons, and ligaments. Together, these structures support body weight, protect vital organs and provide a framework that muscles can pull against to produce movement. Bones also store minerals, while bone marrow contributes to blood cell production.
An adult human skeleton typically contains 206 bones. At birth, there are about 260 bones, but many fuse as the body develops. These bones in human body are organised into two main divisions: the axial skeleton and the appendicular skeleton. Understanding these divisions makes it easier to identify the major skeletal system parts and their roles.

A simple skeletal system definition is the body’s internal support system made mainly of bones and associated connective structures. The skeletal system in human body provides shape and stability while also protecting organs and supporting movement.
The major human skeletal system parts are divided into:
• Axial skeleton: Forms the body’s central axis and includes the skull, vertebral column and thoracic cage.
• Appendicular skeleton: Includes the limbs and the girdles that attach them to the axial skeleton.
A labelled skeletal system diagram can help visualise how these two divisions fit together and where the major bones are located.

The axial skeleton contains 80 bones and forms the central framework of the head, neck, chest and back.
SkullThe skull protects the brain and supports the structures of the face. It contains 22 bones: 8 cranial bones and 14 facial bones. The hyoid bone and six auditory ossicles are also associated with the skull region and are counted separately within the axial skeleton.
The cranial bones include the frontal, parietal, temporal, occipital, sphenoid and ethmoid bones. The facial bones include the maxillae, mandible, zygomatic, nasal, lacrimal, palatine and other bones that form the facial framework.
The stapes, one of the three auditory ossicles in each middle ear, is the smallest bone in the human body.
Vertebral ColumnThe vertebral column supports the head and trunk and protects the spinal cord. It develops from about 33 vertebrae, several of which later fuse. In adults, it is counted as 26 bones: 24 separate vertebrae plus the sacrum and coccyx.
The spine includes 7 cervical, 12 thoracic and 5 lumbar vertebrae, followed by the fused sacrum and coccyx. Its natural cervical, thoracic, lumbar and sacrococcygeal curves improve strength and flexibility and help distribute shock during movement.
Thoracic CageThe thoracic cage protects organs such as the heart and lungs. It includes the ribs, sternum, thoracic vertebrae and costal cartilages.
Humans have 12 pairs of ribs. The first 7 pairs are true ribs, which connect directly to the sternum through their own costal cartilage. Ribs 8–12 are false ribs, while ribs 11 and 12 are also called floating ribs because they have no anterior attachment to the sternum.

The appendicular skeleton contains 126 bones. It includes the upper and lower limbs as well as the pectoral and pelvic girdles. These structures allow the limbs to connect with the body’s central framework.
Pectoral Girdle and Upper LimbsThe pectoral girdle contains 4 bones: 2 clavicles and 2 scapulae. It connects the upper limbs to the axial skeleton.
Each upper limb has 30 bones, giving 60 in total. These include the humerus, radius, ulna, carpals, metacarpals and phalanges. Together, they form the arm, forearm, wrist and hand.
Pelvic Girdle and Lower LimbsThe pelvic girdle consists of 2 hip bones. Each adult hip bone develops from the fusion of the ilium, ischium and pubis, but is counted as one bone.
Each lower limb contains 30 bones, or 60 across both limbs. These include the femur, patella, tibia, fibula, tarsals, metatarsals and phalanges. The femur is the longest and strongest bone in the human body.
Together, these structures make up the major human skeleton parts involved in support, balance and movement.

There are three major types of skeletal system based on how an organism’s body is supported:
• Hydrostatic skeleton
• Exoskeleton
• Endoskeleton
Humans have an endoskeleton, meaning the skeleton is located inside the body. These categories are also known as the main types of skeleton.

The main skeletal system functions extend beyond simply holding the body upright. The key functions of skeletal system include:
• Support: Bones create the body’s framework and help maintain posture.
• Protection: The skull protects the brain, the vertebral column protects the spinal cord and the rib cage protects the heart and lungs.
• Movement: Bones provide attachment points for muscles and act as levers at joints.
• Blood cell production: Red bone marrow produces red blood cells, white blood cells and platelets.
• Mineral storage: Bones store minerals such as calcium and phosphorus.
• Fat storage: Yellow bone marrow stores fat that can serve as an energy reserve.

Different skeletal system diseases can weaken bones, affect their development or alter their structure. Common examples of skeletal system diseases and disorders include:
• Osteoporosis
• Rickets
• Osteogenesis imperfecta
• Paget’s disease of bone
• Bone infections
• Bone cancer
These conditions differ in their causes and effects, but all can interfere with the normal strength, structure or function of bones.