The placenta (from Latin «tortilla», meaning placenta) is a children place-fetal organ of all the placental mammals, some marsupials, hammerhead fish and other viviparous fish. Also the viviparous onychophora and other groups of animals transfer the material between the circulation systems of fetus and mother trough placenta. In botanic placenta is a carpel section to which the ovule attaches. In mammals the placenta forms from embryonic fetal membranes (villous, CVS, and the urinary bag – allantois) which are attached to the walls of uterus and form the outgrowths (villi), jutting into the mucosa and forming a close link between the embryo and the mothers’ body. This connection serves for nutrition and respiration of the embryo. The umbilical cord connects the fetus and placenta. Placenta with fetal membranes (so called afterbirth) comes out of the reproductive tract of the woman in 5-60 minutes (depends on the tactics of the childbirth) after the birth of the child.
Human placenta (placenta discoidalis) – placenta of the hemochorial type, maternal blood is circulating around the thin villi, which contain fetal capillaries. Since 30-ies, the medicine containing extract of placenta and placenta suspension (developed by professor V.P. Filatov.) is manufactured. Those kinds of medicine are popular enough in pharmacology. The stem cells that are kept in blood banks can be extracted from the umbilical blood and placenta. Placental extracts are also antibacterial and antiviral. The medicine also provides the body with all necessary substrates (vitamins, amino acids) which allows to stimulate the body without depletion of its energetic, plastic and other resources. The presence of the amino acids, enzymes and unique protein regulators allows drugs containing placenta to activate «the dormant» cells of a grown body. That leads to their reproduction, renewing of the cellular composition and finally to rejuvenating. There is a tradition in some countries to take placenta home and dig it under the tree. Placenta was considered sterile till it was proved according to results of research of the project «Microbiom of the human» that its microorganisms are similar to those in mouth cavity of female.
There are several types of animal placenta. Marsupials have the incomplete placenta which causes such a short period of pregnancy (8-40 days). Cloven-hoofed animals have placenta diffusa of the epithelichorial type. Placenta zonaria of endoteliochorial type is observed in predators. Placenta discoid (hemochorial type) in rodents and human and placenta cotyledonaria or multiplex placenta- in ruminants. Most female mammals, including herbivores (cows and other ruminants) eat their afterbirth right after licking the newborn. It is done not only to eliminate the blood smell that may attract predators, but also to provide themselves with vitamins and nutrients they need after giving birth.
The formation and structure of the placenta
Placenta if formed of the endometrium and cytotrophoblast in the mucous membrane of the posterior wall of the uterus.
The layers of placenta (from fetus to the uterus-histologically):
- Decidua-transformed endometrium (with decidual cells rich in glycogen);
- Rohr fibrinoid (Lanthanses layer);
- Trophoblast covering the gaps and growing into the walls of spiral arteries, preventing their reduction;
- Lacunas filled with blood;
- Syncytiotrophoblast (multicore symplast covering cytotrophoblast);
- Cytotrophoblast ( separate cells forming syncytia and secreting biologically active substances);
- The stroma (connective tissue containing blood vessels, Kashchenko-Gofbauera cells – macrophages);
- Amnion (placental synthesize amniotic fluids, non placental-absorbing).
Decidua membrane and the socket with maternal blood are placed between the fetal and maternal parts of placenta-basal. This part of placenta is divided into the 15-20 cup-shaped spaces (cotyledons) by decidua septum. Each of them comprises the main branch, consisting of umbilical blood vessels of the fetus. Those branch out further in number of chorionic villi that make up the surface of cotyledon. Due to the presence of placental barrier the blood flow of the mother and fetus is not connected. Exchange of materials is performed with the help of diffusion, osmosis or active transporting. From the third week of pregnancy, when the heart of the child starts beating the fetus is supplied with oxygen and nutrients through placenta. The forming does not have a clear structure till the 12 week of pregnancy. Before the 6th week of pregnancy it is placed around the ovum and is called chorion. Placentation takes place on 3rd – 6th week.
Placenta forms the barrier, which is represented by the layer of vascular endothelial cells, their basal membrane, a layer of loose connective precapillary tissue, basal membrane of trophoblast, layers of cytotrophoblast and syncytiotrophoblast. The vessels of the fetus branching in placenta to the smallest capillaries form (accompanied with supporting tissues) chorionic villi, which are immersed into the gaps filled with maternal blood. Thus placenta performs the following functions :
The oxygen from maternal blood enters the fetal blood according to simple laws of diffusion. Carbon dioxide is transported back.
Trophic and excretory
The fetus receives water, electrolytes, nutrients and minerals, vitamins through placenta. Also placenta takes part in removal of metabolites (urea, creatine, creatinine) by means of active and passive transporting.
Placenta performs endocrine function. The chorionic gonadotropin, which supports the functional activity of placenta and stimulating the production of progesterone by corpus luteum is formed in it. Also the placental lactogen that plays the important role in ripening and development of mammary glands during pregnancy and their preparation for lactating is produced by placenta. Prolactin that is responsible for lactation, progesterone that is responsible for endometrium growth and preventing the release of new ovums. Also the estrogen which causes the hyper trophy of the endometrium is so produced by placenta. Placenta is also able to produce testosterone, serotonin, relaxin and some other hormones.
Placenta has the immunity-conferring properties. It transports the maternal antibodies to the fetus providing the immunological protection. Part of antibodies proceed through the placenta protecting the fetus. Placenta plays an important role in regulation and development of maternal immune system and that of the fetus. At the same time it prevents the immune conflict between mother and fetus. Maternal immune cells could possibly reject the fetus. Syncytium absorbs some of the substances that are circulating in maternal blood and prevents their entering into the blood of fetus. However placenta does not protect the fetus from certain drugs, pills, alcohol, nicotine and viruses.