The human body is a complex collection of organs and systems that work together to keep us alive and healthy. Some organs, such as the heart, are necessary to sustain life. But the human body is able to do without part or all of some organs, despite their useful functions.
The human body typically comes equipped with two lungs that are divided into sections called lobes. At least one lung is necessary to add oxygen to the blood. If all or part of a lung is removed, the remaining lung may expand to take on some of the work of the missing lung.
A person with one lung will probably have a harder time breathing, and will not be able to exercise as strenuously as a person with two healthy lungs.
The human body normally has two kidneys, which act as filters to remove impurities in the blood. Some people are born with one kidney. Others have a kidney surgically removed, either because it is diseased or because they've chosen to donate a kidney to someone whose kidneys have failed.
It is possible to live a normal life with just one kidney. It is also possible to live with no kidneys. This is done by undergoing regular kidney dialysis which uses a machine to remove waste from the blood.
The spleen is an organ that helps filter the blood. It also acts as a reservoir for immune cells called monocytes. These immune cells are important in the healing of the body after trauma such as a heart attack, a wound with excessive bleeding, or certain types of infections. People can live without a spleen, but may be more prone to certain types of infections.
The reproductive organs of both men and women, including the testes and uterus, are necessary to create a child. But they are not necessary to sustain the life of the parent. Many people have their reproductive organs removed as a treatment for cancer or other diseases.
Despite the body’s constant need for nourishment, it is possible to live without a stomach.