Answer
Implantation of the blastocyst into the endometrium begins about the sixth day after fertilization. At first, the blastocyst attaches lightly to a proximal area of the actively secreting endometrium ( fundus or body, usually). In this process the blastocyst orients so that the inner cell mass faces the endometrium. . By the seventh day after fertilization, the blastocyst become more firmly attached and the endometrium becomes more vascular and secretory,
Work Step by Step
The bastocyst proceeds to secrete enzymes which facilitate its burrowing into the tissue of the endometrium. In response the endometrium grows over and covers the blastocyst. The blastocyst is then truly implanted, and the endometrium becomes the decidua.
