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 menstrual cycle is controlled by estrogen and progesterone. Around day 5 of the cycle the endometrium thickens due to rising levels of estrogen and then progesterone. Estrogen is initially secreted by the maturing follicle and then the corpus luteum secretes estrogen and progesterone.