implantation

1. 1. The act or an instance of implanting.
   2. The condition of being implanted.
2. Embryology. The process by which a fertilized egg implants in the uterine lining.

Implantation of an embryo into the lining of the uterus occurs a week or so after an ovum has been fertilized in one of the Fallopian tubes. The uterine lining has been routinely prepared to receive it in the second half of the menstrual cycle, but the mother's body does not ‘know’ that there is an embryo on the way until it has become embedded and can send hormonal signals via the maternal blood to the ovary whence its ovum came. This chorionic gonadotrophin makes the ovary continue to secrete progesterone, which in turn, via the blood, makes the uterus maintain its welcoming lining, avoiding the catastrophe (for an embryo) of menstruation. The embryo implants itself by passing though the outer cellular layer of the uterine lining, assisted by chemicals which it secretes. At this stage it is more or less spherical and covered with villi (frond-like protrusions) ; these provide a large surface area for exchange of gases, nutrients, water and waste with the maternal blood.

— Stuart Judge

See pregnancy.

1. the insertion of an organ or tissue in a new site in the body.
2. the attachment and embedding of the fertilized ovum in the endometrium.
3. the insertion or grafting into the body of biological, living, inert or radioactive material. Includes the planting of needles, staples or beads for prolonged stimulation of acupuncture points for a long term effect.

• embryo i. — attachment of the trophoblast to the uterine lining. The form of attachment varies widely from superficial apposition to varying degrees of endometrial invasion.