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There is confusion in understanding of organs and organ systems.  

Organs are:
      larynx, trachea, bronchi, pleurae, lungs, mouth, fauces, pharynx, esophagus, abdomen, stomach, intestines small and large, liver, pancreas, kidneys, ureters, urinary bladder, various glands, reproductive organs, organs related to our senses,  other organs related to brain & nerves, etc.

Organ systems are
     Circulatory systems (Cardiovascular system for blood, and the Lymphatic system), Digestive system, Endocrine system (communication within body), excretory system (fluid and electrolyte balance – urinary system), Nervous system (collection and transfer and processing of information), immune system (defence against diseases), muscular system, Integumentary system(skin, hair, breasts), reproductive system, respiratory system, skeletal system  

Organs involved
are the stomach, intestines, pancreas, hypothalamus in the brain, ...

 Organ systems involved are Digestive system, Endocrine system, Nervous system, Circulatory system.  

     Our body and system feels the urge and need to eat food. This sensation is called hunger.   Digestive system maintains the sugar levels in the blood. When the level falls below a certain threshold (or when stomach is empty), a harmone Ghrelin is secreted in the stomach. Ghrelin is also called the hunger harmone. It is produced in gastro-intestinal tract. After eating food, the stomach gets stretched the ghrelin secretion stops. Ghrelin acts on the hypothalamic brain cells of our central nervous system

After about half a day of digestion of food, the stomach muscles start to contract and cause pain. These are called hunger pangs.

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