There is only one heart, liver, gallbladder, spleen and stomach, bladder, brain, two lungs and two kidneys, and the skin and intestines cannot be counted. As far as the digestive system you mentioned is concerned, the stomach, gallbladder, pancreas and intestine belong to the digestive system, and the lungs belong to the respiratory system. Kidney and bladder belong to urinary system, skin belongs to immune system, heart belongs to cardiovascular system, and brain belongs to nervous system. Skin also belongs to the sensory system. Pancreas, gallbladder and spleen all belong to endocrine system.