The duodenum is a part of the digestive system in the human body. The digestive system is responsible for the breakdown and absorption of nutrients from food. It consists of various organs including the mouth, esophagus, stomach, small and large intestines, and the duodenum.
Option 2: The excretory system is responsible for removing waste and toxins from the body, primarily through urine production. The duodenum is not involved in excretion, so this option is incorrect.
Option 3: The reproductive system is responsible for the production and transportation of gametes (sperm and eggs) and for the development and nourishment of offspring. The duodenum is not part of the reproductive system, so this option is incorrect.
Option 4: The respiratory system is responsible for the exchange of gases, primarily oxygen and carbon dioxide, between the body and the environment. The duodenum is not involved in respiration, so this option is incorrect.
In conclusion, the correct option is 1: Digestive system.