Implantation (human embryo)

The nidation ( implantation, according to the Latin nidus, nest ) or implantation ( implantation, according to the Latin plantatus planted ) is the implantation of the fertilized ovum in the blastocyst stage in the uterine lining. The nidation starts with people on the fifth or sixth day after fertilization of the egg. The einnistende to blastocyst secretes the hormone hCG ( human chorionic gonadotropin), which prevents the shedding of the uterine lining during the menstrual period.

Fertilization and implantation in humans

The fusion of egg and sperm takes place 12-24 hours after ovulation (ovulation) in the oviduct ( fallopian tube ). The fertilized egg, also called a zygote divides and is moved by the cilia of the fallopian tube towards the uterus cells. Approximately 12- 16- cell stage reaches the zygote - referred to this time as a morula - on the third day after fertilization the uterine cavity. By further divisions and structural changes resulting from the morula blastocyst. This is characterized by the fact that the cells from which the embryo is apparent ( embryoblast ), accumulate on one side of the blastocyst. The wall of the blastocyst is formed of flattened cells, which are referred to as a trophoblast. The trophoblast surrounds the blastocyst cavity.

The implantation begins with the attachment of the blastocyst to the uterine lining (endometrium ) between the 5th and 6th days. Then penetrate those trophoblast cells, which are located at the pole of the blastocyst, where the embryoblast lies between the surface of cells ( epithelial cells) of the uterine lining one. For this, pour the trophoblast cells of enzymes, structural proteins of the connective tissue of the mucous membrane dissolve ( proteolytic enzymes). Also, the cells of the lining of the uterus to support implantation of the blastocyst. The whole process of implantation lasts until the end of the second week of development. The blastocyst is then completely penetrated into the upper layer of the uterine lining and is covered by newly formed epithelium. It is in fact an implantation in the uterus, and not merely a attachment.

The implant is connected to the opening of some blood vessels in the lining of the uterus so that it may be a slight bleeding, called implantation bleeding. At this time, the next, now lack of menstrual bleeding would be due, the haemorrhage implantation can be confused with these. The woman can thus mistakenly assume at this time that she was not pregnant.

Site of implantation

The implantation occurs in humans usually on the rear wall of the uterus, very rarely also outside the uterus, if it comes to passage disturbances in the area of the fallopian tube. In these cases, an ectopic pregnancy, which in 99 % of cases, the fallopian tube itself to the place which is called ectopic pregnancy occurs. In the remaining cases, the embryo / the blastocyst implants in the abdominal cavity, usually in a pouch of Douglas or the mesentery. Such pregnancies outside the uterus are also ectopically called (from the Greek ek, out of, and topos, place), since they are located outside the natural place for a pregnancy.

An ectopic pregnancy can endanger the mother's life to a great extent, especially because can tear blood vessels with the Greater Will of the embryo. Nevertheless, it is in rare cases, the birth of a ectopically term baby.

Inhibition of nidation

For some methods of contraception is discussed as a possible mechanism of inhibition of nidation. Especially with intrauterine devices ( " spiral" ), in which emergency contraception ( " morning after pill " ) and the mini pill could contribute to the inhibition of implantation contraceptive effect. In general, the so-called " spiral thereafter " is used to perform an interception (prevention of implantation of the egg after fertilization ). Evidence of nidationshemmende effect of these methods do not exist. Due to the possible effect nidationshemmenden these methods of some churches such as the Orthodox Churches and the Catholic Church, to be rejected, since, according to their doctrine that human life begins with the fusion of egg and sperm cell.

Under German criminal law, pregnancy does not begin until the time of implantation.

Literature and sources

• T. Sadler: Medical Embryology. 10th edition. Thieme, Stuttgart, 2003. P.25 - 44th ISBN 3-13-446610-4