12. The Muscular System and Digestive System in Human Beings

Muscular system

Close your fist tightly and bend your arm at the elbow. Now feel the upper part of this arm with the fingers of your other hand. What did you experience ? Did you feel the hardness in the upper arm ? This fleshy part consists of muscle. Muscles contract and relax as different parts of our body move. Muscles give our body a specific shape and posture. Muscles are bundles of fibres that can contract and relax as required.

Muscles are firmly attached to bones by means of tendons. When muscles contract, there is movement at the joint and the bones move either nearer to or away from each other.

The action of muscles is necessary for all kinds of movements – from the small movements of eyelids to those that demand great strength as when chopping wood with an axe. We use muscles for various movements like talking, laughing, walking, jumping, throwing, etc.

  1. Voluntary muscles : Working with our hands, walking, eating, etc. are functions that depend upon our will. Muscles used in these actions are called voluntary muscles. For example, muscles in our arms and legs are voluntary muscles.
  2. Involuntary muscles : Various processes like breathing, blood circulation, digestion are vital functions, i.e., they are essential for life. They do not depend upon our will. The muscles of organs which carry out these involuntary functions are called involuntary muscles. Functions of organs like the stomach, intestine, heart are carried out in their own fixed manner by involuntary muscles.

 Which organs in our body have voluntary muscles and which ones have involuntary muscles? Find out and make a list of each type.

Types of muscles

  1. Skeletal muscles : The two ends of each of these muscles are attached to two different bones. Examples of such muscles are muscles of the arms and legs. Their movements are voluntary. They are also responsible for holding the bones of the skeleton together and giving shape to our body.
  2. Heart or cardiac muscles : These muscles bring about the contraction and relaxation (beating) of the heart. Their movement is involuntary. Cardiac muscles cause our heart to relax and contract continuously at a rate of about 70 times per minute.
  3. Smooth muscles : These muscles are present in the internal organs other than the heart. For example, muscles of the stomach, intestine, blood vessels, uterus, etc. Their movements are involuntary and slow. Various vital functions of our body, of which we remain quite unaware, are carried out by these special muscles.

Muscles of which part of your arm contracted and relaxed during the above three actions ? Muscles in our body always work in groups. When some muscles contract, other muscles of the same group, relax. This is how muscles help in the proper performance of the various functions of our body.

The muscle on the front of the bone in our upper arm is called the biceps. The muscle at the back is called the triceps.

Digestive system

Conversion of food into a soluble form and its absorption into the blood is called digestion. The digestive system consists of the alimentary canal and digestive glands. The total length of alimentary canal is about 9 metres. Its main parts are the mouth, pharynx, oesophagus, stomach, small intestine, large intestine, rectum and anus. The salivary glands, liver and pancreas are the digestive glands connected to the alimentary canal.

 Different organs of the digestive system systematically perform the function of digestion. There are different stages in the process of digestion of food and at each stage there is a different organ of the digestive system which performs its specific role. Let us study the structure and function of each organ of the digestive system.


 The process of digestion begins with the function of the teeth in the mouth. There are four types of teeth, namely, incisors, canines, pre-molars and molars. Each type of tooth has a specific function. Each tooth is covered by a hard substance called enamel. Enamel is made of a calcium salt. Saliva contains an enzyme called ptyalin or salivary amylase. Ptyalin converts starch into a sugar called maltose.