EVS Answer The Following question.

The oxygen present in the inhaled air enters the blood due to the respiratory system. The food is digested and it also enters the blood due to the digestive system. The blood then flows to every part of the body due to circulatory system and it supplies the digested food and oxygen.

The food acts as fuel and it bums slowly in presence of oxygen releasing energy. This energy is then used by various parts of the body to do work. Thus the respiratory system, digestive system and circulatory system work together to provide the body with energy.

The inner lining of the respiratory tract secretes a sticky substance called mucus. It also has hair-like structures called cilia. The air that we inhale is purified with the help of this mucus and cilia. The cilia filter the dust, smoke, micro-organisms etc. and these substances get entangled in the sticky mucus and stick to the inner lining of the nose. Sometimes the cilia push out these substances towards the nostrils which is then blown out by sneezing. Thus this is how air that we inhale is purified.

The food that we chew in the mouth enters the oesophagus after swallowing. The upper ends of both the oesophagus and the windpipe open in the throat next to each other. When we swallow the food in a hurry while eating, sometimes the food suddenly enters the windpipe causing us to suddenly choke.

When we eat food the nerve present in the nose and tongue send the message via the network of nerves to the brain. The brain then sends the message to the salivary gland to secrete the saliva. This is how the salivary glands comes to know that there is food in the mouth and it needs to secrete saliva.

When the food absorbed in the blood gets exhausted, after release of energy, the message reaches the brain via the network of nerves. Due to this, the brain then gets the signal that the body needs food. We realise we are hungry and we need to eat food.