The main purpose of the excretory system is to rid the body of unwanted materials. These range from ingested materials that can't be broken down (fiber), too much of something that the body needs to level out (water), or molecules created through respiration and other processes that are now toxic...
The main purpose of the excretory system is to rid the body of unwanted materials. These range from ingested materials that can't be broken down (fiber), too much of something that the body needs to level out (water), or molecules created through respiration and other processes that are now toxic to the body (carbon dioxide, urea).
The excretory system is a bit different compared to other systems as it actually encompasses organs from other systems rather than having organs for its one system alone. The excretory system includes the end of your digestive system and tract, your urinary system, your skin, and your respiratory system.
Digestive system: As food is processed in your body, some things cannot be broken down. All digestible material and material that can be absorbed is brought in through the lining of the small intestine. Once the remainder reaches the large intestine all liquid is removed from it and the solid waste is released at the end of the colon.
Urinary: As water and other liquid wastes travel through your circulatory system, excess water needs to be removed to keep your cells in balance. Your renal artery passes through your kidneys (located on your dorsal side, one on each far side) and water is siphoned out by nephrons. Urea, a byproduct of breaking down proteins, is also cleaned out and added to the water, making urine. Urea is the molecule that gives urine its distinctive smell and color. Other by products are removed here and added to your urine to be released from the body via the urethra, like excess salts.
Skin: If you are in a situation where sweat is needed, rather than waste the excess water in your system in urine, water will instead be routed to pores in your skin where sweat glands release it. This helps regulate your body's temperature by allowing the water to evaporate, carrying heat along with it. You also release extra salts and electrolytes that your body does not need, which is why your sweat tastes slightly salty.
Respiratory system: Your airways have two major functions. One of these is to bring in oxygen for your body to use in cellular respiration (how you produce energy from food). The other function is to remove the waste created by respiration, carbon dioxide. In high enough levels CO2 can be toxic, as it begins messing with your pH levels and also prevents the body from bringing in oxygen. The blood carries the CO2 to the lungs much as it picks up oxygen and releases it into the lungs, which you then empty with each exhale.
In conclusion, your excretory system's main purpose is to remove waste from your body. Any harmful byproducts created by other functions and processes in the body are removed by this network of systems. It interacts with every other system of the body and even includes a few under its own jurisdiction. I hope this summary helps!