8. Our Skeletal System and the Skin

Which organ systems do you see in the figure alongside ?

In the previous classes, we have learnt about some organ systems, their functions and their locations in our body. With the help of that, complete the following table.

Sometimes when we fall while playing or have an accident, a bone in our arm or leg may get broken. This is called a ‘fracture’ of the bone. A fracture in a bone causes severe and unbearable pain and the part with the broken bone swells immediately.

Your friend meets with an accident and a bone in his leg is fractured. How will you help? After an accident, prevent any movement of the fractured part. Immobilize it and get immediate medical help. After going to the hospital, an ‘X-ray’ image is taken of the part which is swollen. ‘X-rays’ were discovered by Wilhelm Conrad Roentgen.

An X-ray image shows whether a bone is broken and also the exact spot where it is broken. This helps in providing the proper treatment.

Let’s identify our bones.

(1) Place your hand at the centre of your chest and your friend’s back.
(2) What is the name of the hard part you feel on placing your hand on your chest ?
(3) Do you feel some hard bumps on the back ? What are they called?
(4) What difference do you notice between the bones of the back and those of the chest ?

The human skeletal

system All the bones in our body are not of the same shape. Every bone is different. All the bones together form a framework or skeleton. The skeleton gives a shape to the body. All the bones of the body along with cartilage together form the skeletal system.

 Bones are hard. They are not flexible. Bones are composed of two main constituents. Bone cells are biotic, while calcium carbonate, calcium phosphate, minerals and salts are the abiotic constituents of bones. Calcium imparts strength to the bones.

Take a measuring tape and measure the length of the bones of your arms and legs. Do the same for your friend/ sister/ brother. Record the measurements in the table below and compare them.

The human skeletal system can be divided into two parts : the axial skeleton and the appendicular skeleton. The axial skeleton consists of the skull, the spine and the rib cage. These are situated symmetrically along the central vertical axis of the body. The appendicular skeleton is made up of the bones of the upper and lower limbs (arms and legs) on either side of the central axis.

The axial skeleton

Skull :The skull is formed by the bones of the head and face. The bones of the skull are flat and strong. There are altogether 22 bones in the skull, 8 in the head and 14 in the face. Except for the lower jaw, none of the bones of the skull can move. Which organs of our body does the skull protect ?

Rib cage : Feel the left and right sides of your chest with your hand or finger. How many bones can you feel altogether on the two sides ? Check in the centre. How many bones do you feel ? The cage-like structure in the chest is calld the rib cage. In the chest, there is one vertical, flat bone called the sternum. Twelve pairs of flat bones called ribs are joined to it sideways. These 25 bones form the rib cage. It is joined to the spine at the back.

The Spine (Backbone or Vertebral Column) : The spine is formed by padlock-shaped bones placed straight one above the other. There are altogether 33 bones in the spine, each called a vertebra. These bones are arranged one above the other flexibly. The spine protects the spinal cord that originates from the brain. What would have happened if we didn’t have a backbone ?

The appendicular skeleton

 The human body has two arms and two legs. The different parts of the arms and legs have several bones, which are connected together by joints.

Move the different parts of your body from the head to the toes and observe the different places at which they can bend or turn. The bones in our body are connected to each other by means of ligaments.

Types of joints

Let us study some types of movable joints.

  1. Hinge joint : This type of joint allows the movements of bones only in one direction. It moves in a 1800 angle. Examples : the elbow and knee joints.
  2. Ball and socket joint : In this type of joint, the bones can move in two or more directions – in a 3600 angle. Examples : shoulder and hip joints.
  3. Gliding joint : In this type of joint, the bones can only slide over each other. Examples : wrist and ankle joints.

The skin

The skin is an important and large organ of all living things. The skin has hair. There are nails on the skin at the tips of the fingers and toes. The skin gives us the sense of touch. The skin is an important sensory organ of the body

The structure of the skin
Human skin is made up of two main layers. The outermost layer is called the epidermis and the layer below it is called the dermis. Below the dermis, there is a network of blood vessels and nerve fibres. The subcutaneous layer under this network maintains normal body temperature. The epidermis has various layers.

When we walk or play in the sun, we get tired, but at the same time our skin becomes wet. This is because of sweat. In the skin, there are glands which secrete sweat. They are called sweat glands. After playing in the hot sun or after hard physical labour, the temperature of the body rises. Then sweat is released. It helps to reduce the temperature of the body. Our body temperature usually remains constant at approximately 370 C.

Observe your skin and the skin of your grandmother, grandfather or any old people in the house. What difference do you notice ? As we grow older, the proportion of fat beneath the skin reduces. However, the previously taut skin does not shrink. This causes wrinkles on the skin of older people.