When glucose level is less in blood then a harmone is released known as ghrelin then we feel hungry.  then hunger is controlled when leptin is released.

Well, a major cause for feeling hungry lies in the physiology of blood.glucose is one of the major substance present in blood.When its levels fall,we get hunger pangs in stomach.during this ghrelin hormone is secreted from the walls of stomach & the signals reach the brain.Hunger pangs continue to 30-45 min.Diencephalon and vagus nerve plays an important role in carrying these signals to brain.Increase in ghrelin levels results in sensation of hunger & motivation to consume food
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