Some gases are lighter than air. Hydrogen is the lightest of all, and easily manufactured, even at home -- for example by dropping aluminium foil into a solution of sodium hydroxide (highly dangerous because it will spit droplets of hot caustic liquid at you which may blind you permanently if they land in your eyes).
The corpus luteum is essential for establishing and maintaining pregnancy in females. The corpus luteum secretes progesterone, which is a steroid hormone responsible for the decidualization of the endometrium (its development) and maintenance, respectively. It also produces relaxin, a hormone responsible for softening of the pubic symphysis which helps in parturition.
The goal of medical treatment of endometriosis is to increase the ratio of progesterone to estrogen (progesterone only treatment), decrease the amount of both estrogen and progesterone (combinational birth control pills) or to eliminate estrogen from the body (GnRH treatments such as Lupron).