To speak about internal organs, you need the appropriate vocabulary.
Stomach - the organ inside your body where food goes after it has been eaten and where it starts to be digested;
Lung - one of the two organs inside your chest that are used for breathing;
Brain - the organ inside your head that controls your thoughts, feelings, and movements;
Tissue - the material that animals and plants are made of;
Spine, backbone, spinal column - the long structure of bones down the centre of your back, which supports your body;
Kidney - one of the two organs in your body which remove waste from the blood and produce urine;
Heart - the organ inside your chest that sends blood around your body;
Skeleton - the structure made of all the bones in the body of a person or animal;
Skull - the part of your head that is made of bone and which protects your brain.
Examples:
Some people can have problems with their lungs because of smoking.
She will have an operation on the heart.
Fast food destroys your stomach.