For this purpose, the placenta uses several mechanisms :

It secretes neurokinin B-containing phosphocholine molecules. This is the same mechanism used by parasitic nematodes to avoid detection by the immune system of their host. There is presence of small lymphocytic suppressor cells in the fetus that inhibit maternal cytotoxic T cells by inhibiting the response to interleukin 2.However, the placental barrier is not the sole means of evading the immune system, as foreign fetal cells also persist in the maternal circulation, on the other side of the placental barrier. Other
The placenta also provides a reservoir of blood for the fetus, delivering blood to it in case of hypotension and vice versa, comparable to a capacitor. Clinical significance
Numerous pathologies can affect the placenta. Placenta accreta, when the placenta implants too deeply, all the way to the actual muscle of uterine wall (without penetrating it)
Placenta praevia, when the placement of the placenta is too close to or blocks the cervix
Placental abruption, premature detachment of the placenta
Placentitis, inflammation of the placenta, such as by TORCH infections. Society and culture
The placenta often plays an important role in various cultures, with many societies conducting rituals regarding its disposal. In the Western world, the placenta is most often incinerated.Some cultures bury the placenta for various reasons. The Māori of New Zealand traditionally bury the placenta from a newborn child to emphasize the relationship between humans and the earth. Likewise, the Navajo bury the placenta and umbilical cord at a specially chosen site, particularly if the baby dies during birth.
The Koebner phenomenon or Köbner phenomenon (UK: , US: ), also called the Koebner response or the isomorphic response, attributed to Heinrich Köbner, is the appearance of skin lesions on lines of trauma. The Koebner phenomenon may result from either a linear exposure or irritation. Conditions demonstrating linear lesions after a linear exposure to a causative agent include: molluscum contagiosum, warts and toxicodendron dermatitis (a dermatitis caused by a genus of plants including poison ivy). Warts and molluscum contagiosum lesions can be spread in linear patterns by self-scratching ("auto-inoculation"). Toxicodendron dermatitis lesions are often linear from brushing up against the plant. Causes of the Koebner phenomenon that are secondary to scratching rather than an infective or chemical cause include vitiligo, psoriasis, lichen planus, lichen nitidus, pityriasis rubra pilaris, and keratosis follicularis (Darier disease). Definition
The Koebner phenomenon describes skin lesions which appear at the site of injury. It is seen in:
Psoriasis
Pityriasis rubra pilaris
Lichen planus
Flat warts
Lichen nitidus
Vitiligo
Lichen sclerosus
Elastosis perforans serpiginosa
Kaposi sarcoma
Necrobiosis lipoidica
Lupus
Juvenile Idiopathic Arthritis
Still disease
Cutaneous leishmaniasis
Post kala azar dermal leishmaniasisA similar response occurs in pyoderma gangrenosum and Behcets syndrome, and is referred to as pathergy.Rarely Koebner phenomenon has been reported as a mechanism of acute myeloid leukemia dissemination.Warts and molluscum contagiosum are often listed as causing a Koebner reaction, but this is by direct inoculation of viral particles.The linear arrangement of skin lesions in the Koebner phenomenon can be contrasted to both lines of Blaschko and dermatomal distributions.