Introduction to Human Skeletal System

The human skeletal system is a framework that gives proper shape and provides protection to the body. For an overview of the human skeletal system, read on...
Bodytomy Staff
Imagine a building without its steel framework. It would just be a mass of cement. Similarly, the human body without a skeletal system, will just be a bag of muscles, without any shape or structure. The human skeletal system is made up of different types of bones and joints. Here's a brief introduction to the human skeletal system is given below.
Formation of Human Skeletal System
The process by which bones are formed is called ossification. Ossification is a life-long process. There are two types of ossification:
Endochronal Ossification: When the fetus is in the early phase of development, it has a skeleton made up of cartilages. These cartilages develop gradually into bones, by the process of endochronal ossification. Bones like femur (thigh bone) are formed from this process.
Intramembranous Ossification: Here, bones are formed from a connective bone tissue made of cells called mesenchyme cells. Skulls bones are formed by this process.
Organization of Human Skeletal System
The human skeletal system is perpendicularly symmetrical in nature. It consists of the axial skeleton and the appendicular skeleton.
Axial Skeleton
The axial skeleton is made up of 80 bones. The main function of the axial skeleton is the protection of organs, like heart, brain and lungs and maintaining the upright position of the body. 633 skeletal muscles act on the axial skeleton. The following table gives information about the organization of the axial skeleton.

Name of the Group of Bones Total Number of Bones
Vertebral column 26
Thoracic cage 12 pairs of ribs
Sternum 1
Skull 29
Appendicular Skeleton
It is made up of 126 bones and is attached to the axial skeleton. It protects the organs involved in reproduction, excretion and digestion. Body movements are possible because of these bones. The following table gives brief information about the organization of the appendicular skeleton.

Name of the Group of Bones Total Number of Bones
Pectoral girdles (Shoulder portion) 4
Upper limbs (Arms) 60
Pelvic girdle (Hip portion) 2
Lower limbs (Legs) 60
Functions of Human Skeletal System
An introduction to human skeletal system will be incomplete without a description of its functions. These functions are listed below.

Support: The human skeletal system gives proper shape to the body. It is a framework that supports body organs and muscles.
Body Movements: The joints present between different bones allow body movements.
Producing Stem Cells: Stem cells are produced in the bone marrow, which is a part of the skeleton. These stem cells further develop into RBCs, WBCs and platelets.
Storage of Calcium and Iron: Bones can store calcium and iron. About 99% of the calcium in the body is stored in bones. They help in iron and calcium metabolism.
Role in Endocrine System: Osteocalcin is the hormone which regulates fat deposition and glucose. This hormone is released by the bones.
Protection: It's the most important function of the human skeletal system. The following table illustrates the organs and the bones which protect them.
Organs Bones
Brain Skull
Lungs, Heart Rib cage
Shoulder Clavicle, Scapula
Knee, Elbow Patella, Ulna
Wrist, Ankle Carpals, Tarsals
Difference between Male and Female Human Skeletal Systems
There are number of differences between the male and the female skeletal system. The pelvis (bone in hip portion) is larger and flatter in females, so as to make it easy for childbirth. Bones in females are rounder and smaller than in males. Men have more squared jaws and pronounced eyebrow ridges. Shoulder blades in females are rounder than in their male counterparts.
Bones
A newborn baby has approximately 230 bones; while an adult, on an average, has 206 bones. Human skeletal system is made up of 5 types of bones. These are:

Long Bones: Their length is greater than their width. Limb bones are long bones. (Carpals or wrist bones and tarsals or foot bones are exceptions.)
Short bones: Their length and width is approximately equal. Carpals and tarsals are small bones. They help in little movements.
Flat Bones: Their main function is to protect body organs. They are flat and act as a base for muscle attachments. Sternum or breast bone, scapula or shoulder blade and the skull are some examples of flat bones.
Irregular Bones: Bones in the vertebral column and mandible (lower jaw) fall under this category. They have an irregular shape.
Sesamoid Bones: These are small bones present in the joints to protect the tendons (fibrous connective tissues that connect muscles to the bones). Patella or knee cap is an example of such bones.
Joints
When two or more bones meet, a joint is formed. They enable different body movements. There are 3 types of joints, they are:

Immovable Joints: They are also called fibrous joints. As the name suggests, they cannot move. Skull bones are immovable joints.
Slightly Movable Joints: These are also called cartilaginous joints. The intervertebral discs come under this category.
Freely Movable Joints: Also called synovial joints, these joints are freely movable and help the body to move. Limbs are an example of synovial joints.
The human skeletal system is equally important, when compared to other body systems. It gives our body a definite shape, structure and protects the vital organs. It can be called the basic infrastructure of our body, without which the human body would have been a ball-like structure rolling on the floor.