IMPLANTATION
INTRODUCTION:-
DEFINITION:-
Penetration of the blastocyst into the superficial [compact] layer of the endometrium.
The endometrium after implantation is called decidua.
TIME:-
Implantation occurs at the 7th day after fertilization and is completed about the 11th day.
SITE OF IMPLANTATION:-
Posterior wall of the uterine body in the functional layer of the endometrium during the secretory phase of the cycle.
STAGES OF IMPLANTATION:-
1. HATCHING
2. ADPLANTATION
3. APPOSITION
4. ADHERSION
5. INVASION
1. HATCHING:-
The blastocyst surrounded by zona pellucida enters into the uterine cavity on day 5.
The blastocyst enlarges, the zona pellucida disintegrates, and blastocyst is released on day 6.
It is called 'HATCHING OF BLASTOCYST'.
2. ADPLANTATION:-
Blastocyst slowly "rolls" On surface, aligns with the ICM close to the epithelium.
3. APPOSITION:-
The very first, loose connection between the blastocyst and the endometrium.
4. ADHERSION:-
The trophoblasts adhere by penetrating the endometrium, with protrusion of trophoblast cells.
5. INVASION:-
Invading into the uterine stroma.
ABNORMAL SITEs OF IMPLANTATION:-
These may be within the uterus or outside the uterus
1. Abnormal sites of implantation within the uterus: In the lower uterine segment near the internal os. It is called as placenta.
2. Abnormal sites of implantation outside the uterus.
(a) In the uterine tube (tubal implantation): Here it may take place (a) in the ampulla, (b) in the infundibulum, or (c) in the interstitial part in order of frequency of occurrence.
(b) In the abdominal cavity (abdominal implantation):Here it implants (a) most frequently in the peritoneal lining of the rectouterine pouch (pouch of Douglas); (b) but may implant at any place covered by peritoneum, e.g., mesentery.
(c) In the ovary (ovarian implantation): Fertilization and implantation may occur while ovum is still within the ovary.
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