Together the esophagus stomach and intestines are part of an

They are the part of digestive system.  i.e organ-system

esophagus > from where food reaches the stomach
stomach > place where the food reacts with different chemicals to release
                        the energy
intestines >place where wastes are stored to get ejaculated out from
                       the  body . Large intestine also absorbs water and small intestines
                        absorb the nutrients

You can do planks so harden ur breast. in case there not strong enough to hold their own weight.