The corpus luteum in pregnancy has a long life. However,if fertilization does not take place,it remains active only for $10-12$ days. Explain.

(N/A) After ovulation,the ruptured Graafian follicle transforms into the corpus luteum,which secretes large amounts of progesterone.
Progesterone is essential for maintaining the endometrium,which is necessary for the implantation of the fertilized ovum (zygote) and the subsequent maintenance of pregnancy.
In the event of pregnancy,the corpus luteum persists to support the developing embryo.
However,in the absence of fertilization,the high levels of progesterone are no longer required to maintain the endometrium.
Consequently,the corpus luteum degenerates within $10-12$ days,leading to the breakdown of the endometrium and the onset of menstruation.