The human body is a complex structure comprising of various important organs. Various organs are well connected and the brain controls the overall functions of the body.
A normal adult human body contains around five litres of blood. The blood plays the vital role of carrying the oxygen we breathe and nutrients in our food to different organs. The quantity of its flow to any organ depends on the importance of the function the organ plays at a given time and also the oxygen and nutrition requirement of the tissues of the organ.
Under normal conditions, brain gets around one sixth, kidneys about one –fourth and liver about one third of the blood pumped by the heart and the remaining is used by other parts of the body including muscles.
After a lunch, the food needs to be digested. At the same time, blood absorbs the nutrients. Thus the focus of the body gets shifted to digesting the food that results in flow of more blood to stomach walls. This reduces the flow of it to other parts of the body, including brain. As the flow to brain is reduced, the body becomes lazy and sleep sets in. During this time, only important functions of heart and lungs take place uninterruptedly.