The mitochondria isn't considered to be part of the endomembrane system because its structure is not derived from the nuclear envelope, ER, GolgiApparatus, or cell membrane.
The renal tubule would be the vessel within the nephron loops that functions to collect ions and water back into the blood. In addition, these vessels are the one responsible for emptying the collecting duct and reabsorbs salts present in the bloodstream and disperses it back to the blood.
The most common elements present in organic compounds are carbon, hydrogen, oxygen, and nitrogen.