c. The combined ovum and sperm, referred to as the zygote, begins rapid cell
division and in 2 to 3 days becomes a structure referred to as morula. The morula is a
rapidly growing structure and reaches the uterus in approximately 4 days.
PROCESS OF IMPLANTATION
a. The morula floats in the uterus for 3 to 4 days, gaining in size and weight. At
this time, the hollow fluid-filled morula, now called blastocyst burrows into the uterine
b. The outer surface of the blastocyst becomes covered with finger-like
projections called chorionic villi. Chorionic villi aid in the process of implantation into the
endometrium (decidua). Villi also manufacture human chorionic gonadotropin (HCG)
which signal the corpus luteum within the ovaries to continue production of
progesterone and estrogen to prevent menstruation.
c. Implantation normally occurs in the upper, posterior wall of the uterus. The
point of implantation becomes the origin for the placenta and umbilical cord.
NOTE: See figure 2-4 for associated events of fertilization and implantation.
2-4. Events of fertilization and implantation.