The formation of the corpus luteum structure takes place after ovulation, primarily due to the activity of LH. The granulosa cells undergo what is known as luteinisation. These luteinised granulosa cells as well as theca cells, capillaries and connective tissue form the corpus luteum. This is responsible for the production of large amounts of oestrogen and progesterone and has a lifespan of approximately 14 days, unless pregnancy occurs.