BGDA Practical Placenta - Implantation and Early Placentation

From Embryology
BGDsmall.jpg
Practical 14: Implantation and Early Placentation | Villi Development | Maternal Decidua | Cord Development | Placental Functions | Diagnostic Techniques | Abnormalities


Early Placenta

Gray0032.jpg Stage5 bf11L.jpg
Human Embryo Day 8 to 9 Human Embryo - early implantation (stage 5)

Uterine surface view of implantation site

Stage5 bf07.jpgStage5 bf04.jpg


Simplified Cartoons


Movies

Week2 001 icon.jpg
 ‎‎Week 2 - Implant
Page | Play
Chorion 001 icon.jpg
 ‎‎Week 2 - Bilaminar
Page | Play
Week3 folding icon.jpg
 ‎‎Week 3
Page | Play
Amnion 001 icon.jpg
 ‎‎Amniotic Cavity
Page | Play


Terms

  • adplantation - The term used to describe the initial process of the blastocyst (conceptus) attachment to the uterine endometrium wall at the site of implanation following hatching from the zona pellucida.
  • cytotrophoblast - The "cellular" trophoblast layer surrounding (forming a "shell") the early implanting conceptus. Beginning at uterine adplantation, proliferation and fusion of these cells is thought to form a second outer trophoblast layer, the syncytiotrophoblast. The cytotrophoblast layer contributes to formation of the placental villi, the functional component of the fetal placenta.
  • decidua basalis - The term given to the uterine endometrium at the site of implantation where signaling transforms the uterine stromal cells (fibroblast-like) into decidual cells. This forms the maternal component of the placenta, the decidualization process gradually spreads through the remainder of the uterus, forming the decidua parietalis.
  • decidualization - The process by which uterine stromal cells differentiate in response to both steroid hormones and embryonic signals into large epitheliod decidual cells. This process is essential for the progress of implantation and establishing fetal-maternal communication.
  • endometrial gland - The mucous secreting gland associated with the epithelium lining the uterus. These glands develop and secrete each menstrual cycle and are thought to provide initial blastocyst nutrition prior to implantation.
  • endometrium - The epithelium lining of the non-pregnant uterus. During pregnancy this epithelium undergoes changes described as the decidual reaction and is renamed the "decidua".
  • extra-embryonic coelom - The space found outside the embryo, amniotic cavity, yolk sac and chorionic cavity.
  • extra-embryonic mesoderm - Cells from the conceptus that contribute to placenta and fetal membranes. Described as "extraembryonic" because it is tissue lying outside the embryonic trilaminar disc (ectoderm, mesoderm and endoderm) and "mesoderm", because of the connective tissue cellular organization. In animal models, this extraembryonic mesoderm has been shown to arise from the same source as embryonic mesoderm during gastrulation.
  • haemochorial - The type of placenta where the chorion comes in direct contact with maternal blood. This is the type of human placentation.
  • implantation - The term used to describe the process of conceptus invasion of the uterus endometrium (epithelium and underlying stroma) by the blastocyst (conceptus). This process follows conceptus adplantation (attachment) to the endometrium. Abnormal implantation is where this process does not occur in the body of the uterus (ectopic) or where the placenta forms incorrectly. In humans, implantation occurs during the second week of development.
  • placenta - (Greek, plakuos = flat cake) The developmental organ formed from maternal and fetal contributions in animals with placental development. In human, the placenta at term is a discoid shape "flat cake" shape; 20 cm diameter, 3 cm thick and weighs 500-600 gm. Placenta are classified by the number of layers between maternal and fetal blood (Haemochorial, Endotheliochorial and Epitheliochorial) and shape (Discoid, Zonary, Cotyledenary and Diffuse). The functional exchange region are the placental villi or chorionic villi. The placenta has many different functions including metabolism, transport and endocrine.
  • syncytiotrophoblast - A multinucleated cell currently thought to form by the fusion of another trophoblast cell the cytotrophoblasts, within the trophoblast layer (shell) of the implanting conceptus. In early development, these cells mediate implantation of the conceptus into the uterine wall and secrete the hormone (human Chorionic Gonadotrophin, hCG) responsible for feedback maintainance of the corpus luteum (in maternal ovary) and therefore maintaining early pregnancy.
  • villi - Plural of villus, which is a thin projection from a surface. A term used to describe the many functional units together of the fetal placenta.
  • villous cytotrophoblast - (VCT) Trophoblast cells located on chorionic villi (as opposed to extravillous cytotrophoblasts) that can also fuse to form the syncytiotrophoblasts.


Implantation and Early Placentation Interactive Component

Attempt the Quiz - Implantation and Early Placentation  
BGDsmall.jpg

Here are a few simple Quiz questions that relate to Implantation and Early Placentation from the practical.

1

During implantation the blastocyst:

  usually implants in the posterior wall of the body of the uterus
  releases substances that cause local changes in the endometrial tissue
  attaches itself to endometrium at its embryonic pole
  all of the above are correct

2

During week 2 (GA week 4) the blastocyst trophectoderm (trophoblast) layer initially differentiates into two layers the:

  hypoblast and trophoblast
  epiblast and primitive yolk sac
  syncytiotrophoblast and cytotrophoblast
  hypoblast and epiblast

3

The intra-embryonic coelom transiently connects to the extra-embryonic coelom.

  false
  true

4

In humans the most common site of implantation is:

  uterine tube
  cervix
  lateral wall of uterus
  posterior wall of uterus
  anterior wall of uterus

5

Which of the following structures are considered extra-embryonic coeloms?

  peritoneal sac
  yolk sac
  allantois
  chorionic sac
  amniotic sac
  pericardial sac


BGDsmall.jpg
Practical 14: Implantation and Early Placentation | Villi Development | Maternal Decidua | Cord Development | Placental Functions | Diagnostic Techniques | Abnormalities


BGDsmall.jpg
Practical 14: Implantation and Early Placentation | Villi Development | Maternal Decidua | Cord Development | Placental Functions | Diagnostic Techniques | Abnormalities


Additional Information

Additional Information - Content shown under this heading is not part of the material covered in this class. It is provided for those students who would like to know about some concepts or current research in topics related to the current class page.


implantation

Placenta Links: placenta | Lecture - Placenta | Lecture Movie | Practical - Placenta | implantation | placental villi | trophoblast | maternal decidua | uterus | endocrine placenta | placental cord | placental membranes | placenta abnormalities | ectopic pregnancy | Stage 13 | Stage 22 | placenta histology | placenta vascular | blood vessel | cord stem cells | 2013 Meeting Presentation | Placenta Terms | Category:Placenta
Historic Embryology - Placenta 
1883 Embryonic Membranes | 1907 Development Atlas | 1909 | 1910 Textbook | 1917 Textbook | 1921 Textbook | 1921 Foetal Membranes |1921 human | 1921 Pig implantation | 1922 Single placental artery | 1923 Placenta Review | 1939 umbilical cord | 1943 human and monkey | 1944 chorionic villus and decidua parietalis | 1946 placenta ageing | 1960 monkey | 1972 Placental circulation | Historic Disclaimer


Placenta Terms (expand to view) 
  • after-birth - term used to describe the delivery of placenta and placental membranes following birth of the child.
  • allantois - An extraembryonic membrane, endoderm in origin extension from the early hindgut, then cloaca into the connecting stalk of placental animals, connected to the superior end of developing bladder. In reptiles and birds, acts as a reservoir for wastes and mediates gas exchange. In mammals is associated/incorporated with connecting stalk/placental cord fetal-maternal interface.
  • amniocentesis - Clinical term for a prenatal diagnostic test where an ultrasound guided needle is used to extract a sample of the amniotic fluid. Amniocentesis
  • anastomosis - Term used to describe the connection between two tubes. Applied to describe the connection between peripheral blood vessels without an intervening capillary bed.
  • anchoring villi - (stem villi) describes the placental villi (embryonic) that attach to the decidua (maternal) tissue. The tip of the villi consists of a column of trophoblast cells attached to an epithelial plaque.
  • angioblasts form clusters or blood islands on surface of yolk sac.
  • angiogenesis - Term describing the development of new vessels from already existing vessels, this process is secondary to vasculogenesis which is the initial formation of first blood vessels by differentiation of pluripotent mesenchymal cells (extraembryonic mesoderm).
  • capsularis - portion of maternal decidua that covers the conceptus facing towards the uterine cavity.
  • cerebroplacental ratio - (CPR) a doppler ultrasound measurement calculated as the simple ratio between the middle cerebral artery pulsatility index (MCA‐PI) and the umbilical artery pulsatility index (UA‐PI). Fetuses with an abnormal ratio are thought to be a predictor of adverse pregnancy outcome.
  • chorioamnionitis - (CA) An intraamniotic puerperal infection described as having 3 forms: histologic, clinical (clinical chorioamnionitis, IAI), and subclinical. Intraamniotic infection is a common (2-4%) event in labor and the systemic inflammatory response can also lead to preterm birth and neonatal complications.
  • chorion - The extraembryonic membrane generated from trophoblast and extraembryonic mesoderm that forms placenta. chorion and amnion are made by the somatopleure. The chorion becomes incorporated into placental development. The avian and reptilian chorion lies beside the egg shell and allows gas exchange.
  • chorionic cavity - The fluid-filled extraembryonic coelom (cavity) formed initially from trophoblast and extraembryonic mesoderm that forms placenta. chorion and amnion are made by the somatopleure. The chorion becomes incorporated into placental development. The avian and reptilian chorion lies beside the egg shell and allows gas exchange. In humans, this cavity is lost during week 8 when the amniotic cavity expands and fuses with the chorion.
  • chorion frondosum - (frondosum = leafy) The chorion found on conceptus oriented towards maternal blood supply where the majority of villi form and proliferate, will contribute the fetal component of the future placenta.
  • chorion laeve - (laeve = smooth) The smooth chorion found on conceptus away from maternal blood supply (towards uterine epithelium and cavity) with very few villi present.
  • chorionic somatomammotropin - (CSH, human lactogen) A hormone synthesized within the placenta by syncytiotrophoblast cells. This protein hormone (190 amino acid) has a structure is similar to pituitary growth hormone.
  • chorionic villus sampling - (CVS) The taking a biopsy of the placenta, usually at the end of the second month of pregnancy, to test the fetus for genetic abnormalities.
  • coelocentesis - A sampling of extracoelomic fluid usually for an early prenatal diagnostic technique.
  • connecting stalk - the original extra-embryonic mesoderm structure attaching the embryonic disc to the chorion. The placental blood vessels form within this structure.
  • cord blood - (human umbilical cord blood, HUCB) A term used to describe blood collected from the placenta usually after birth. Has been identified as a source of stem cells with potential therapeutic uses and is stored in Cord Blood Banks throughout the world.
  • cord knotting Term describing umbilical or placental cord knotting. This occurs in about 1% prevents the passage of placental blood, pseudoknots also occur usually with no effect.
  • cord presentation - A term used to describe at birth the presence of the umbilical cord between the fetal presenting part and the cervix, with or without membrane rupture.
  • cord prolapse - A term used to describe at birth the descent of the umbilical cord through the cervix alongside (occult) or past (overt) the presenting part in the presence of ruptured membranes (incidence of 0.1% to 0.6%).
  • cotyledon - (Greek, kotyle = a deep cup) In the embryos of seed plants, the "seed leaves," in which nutrients are stored for use after germination. In placental animals, the term is also to describe the leaf-like structure of the placenta surface.
  • cytotrophoblast - The "cellular" trophoblast layer surrounding (forming a "shell") the early implanting conceptus. Beginning at uterine adplantation, proliferation and fusion of these cells is thought to form a second outer trophoblast layer, the syncytiotrophoblast. The cytotrophoblast layer contributes to formation of the placental villi, the functional component of the fetal placenta.
  • decidua basalis - The term given to the uterine endometrium at the site of implantation where signaling transforms the uterine stromal cells (fibroblast-like) into decidual cells. This forms the maternal component of the placenta, the decidualization process gradually spreads through the remainder of the uterus, forming the decidua parietalis.
  • decidua basalis reaction - Term describing the maternal endometrial changes that occur initially at the site of, and following, blastocyst implantation. Seen as a deposition of glycogen, fibrin and proliferation of blood vessels. See also decidualization.
  • decidua capsularis - The term given to the uterine endometrium which has been converted to decidua surrounding the conceptus on the smooth chorion side.
  • decidua parietalis - The term given to the remainder of the uterine endometrium, away from the site of implantation, that gradually becomes comverted to decidua.
  • decidual cell - The uterine stromal cells (fibroblast-like) that differentiate in response to both steroid hormones (progesterone) and embryonic signals. These cells then alter uterine environment to support further embryonic development as well as producing cytokines related to prolactin (PRL) and have an innate immune function.
  • decidual reaction - maternal endometrial reaction invoked in order to block the rapid extension of the implanting syncytium.
  • decidualization - (decidualisation, decidual reaction) The process by which uterine stromal cells differentiate in response to both steroid hormones and embryonic signals into large epitheliod decidual cells. This process is essential for the progress of implantation and establishing fetal-maternal communication.
  • DHEA - (dehydroepiandrosterone, androstenolone) precursor of sex steroid hormones and is converted to testosterone and estradiol. Postnatally, an abundant circulating steroid produced in the adrenal gland. The fetal adrenal cortex produces dehydroepiandrosterone sulfate (DHEA-S) used by the placenta to produce estrogens. DHEA, androstenedione, and testosterone can be metabolized to epiandrosterone, and etiocholanolone. PMID 15635500
  • fetal drug addiction - occurs when drugs used maternally cross the placental barrier and can establish neural/physiological addiction in the unborn fetus. drugs
  • fetal erythroblastosis - (Haemolytic Disease of the Newborn) A clinical term describing an immune response between fetal and maternal blood groups; from fetus Rh+ / maternal Rh-. The leakage of blood from fetus, particularly at birth, causes maternal anti-Rh antibodies, which is then dangerous for a 2nd or future pregnancies.
  • fetal intra-abdominal umbilical vein varix - (FIUV, umbilical vein varix) focal dilatation of the umbilical venous diameter at the level of cord insertion, the dilatation diameter increases linearly with gestational age. Represent about 4% of umbilical cord abnormalities

with an incidence of about 2.8 per 1,000 pregnancies, there is also a rarer form of extra-abdominal varices.PMID 24883288

  • fibrinoid layer - (Nitabuch's layer) A layer formed at maternal/fetal interface during placentation and is thought to act to prevent excessively deep conceptus implantation. Fibrin-type fibrinoid (maternal blood-clot product) and matrix-type fibrinoid (secreted by invasive extravillous trophoblast cells).
  • floating chorionic villi - Term used to describe the placental microanatomy structure of chorionic villi that are not attached to the maternal decidua and float in the maternal blood-filled space (lacunae). Structurally the same as anchoring chorionic villi conceptus side that are attached to the maternal decidua.These villi go through the same stages of development: primary villi - secondary villi - tertiary villi
  • hemotrophic nutrition - Term used to describe in late placenta development the transfer of blood-borne nutrition from maternal to embryo/fetuscompared to early histiotrophic nutrition.
  • heterotopic pregnancy - (Greek, heteros = other) Clinical term for a very rare pregnancy of two or more embryos, consisting of both a uterine cavity embryo implantation and an ectopic implantation.
  • histiotrophic nutrition - Term used to describe in early placenta development the intital transfer of nutrition from maternal to embryo (histiotrophic nutrition) compared to later blood-borne nutrition (hemotrophic nutrition). Histotroph is the nutritional material accumulated in spaces between the maternal and fetal tissues, derived from the maternal endometrium and the uterine glands. This nutritional material is absorbed by phagocytosis initially by blastocyst trophectoderm and then by trophoblast of the placenta. in later placental development nutrition is by the exchange of blood-borne materials between the maternal and fetal circulations, hemotrophic nutrition.
  • Hofbauer cells - Cells found within placental villi connective tissue. Have a role as macrophages of mesenchymal origin with potentially additional functions (remodeling, vasculogenesis, regulation of stromal water content).
  • Human chorionic corticotropin - (hCACTH) placental derived hormone equivilant to corticotropin (ACTH) from the pituitary.
  • Human chorionic gonadotrophin - (hCG) like leutenizing hormone, supports corpus luteum, originally secreted by trophoblast cells.
  • Human chorionic somatommotropin - (hCS, placental lactogen) hormone level increases in maternal blood through pregnancy, decreases maternal insulin sensitivity (raising maternal blood glucose levels and decreasing maternal glucose utilization) aiding fetal nutrition.
  • Template:Hydatiform mole - A uterine tumour with "grape-like" placenta appearance without enclosed embryo formation, arises mainly from a haploid sperm fertilizing an egg without a female pronucleus. It is one form of gestational trophoblastic disease(GTD), a number of abnormalities including hydatiform mole, invasive mole, choriocarcinoma and placental site trophoblastic tumor (PSTT).
  • hysterectomy – clinical term for the surgical removal of the uterus.
  • Langhans layer - cytotrophoblast cell layer.
  • maternal antibodies - antibodies from the mother's immune system that are capable of crossing placental barrier. They can provide immune protection to the embryo, but may also participate in immune disease (fetal erythroblastosis).
  • maternal sinusoids - placental spaces around chorionic villi that are filled with maternal blood. This is the closest maternal/fetal exchange site.
  • Nitabuch's layer - (fibrinoid layer) The layer formed at maternal/fetal interface during placentation and is thought to act to prevent excessively deep conceptus implantation. Fibrin-type fibrinoid (maternal blood-clot product) and matrix-type fibrinoid (secreted by invasive extravillous trophoblast cells).
  • Morbidly adherent placenta (MAP) A general clinical term used to describe the different forms of abnormal placental implantation (Accreta, Increta and Percreta).
  • oligohydramnios - Clinical term for the accumulation a deficiency of amniotic fluid during pregnancy. See also polyhydramnios, an excess of amniotic fluid.
  • persistent right umbilical vein - (PRUV) A placental cord abnormality associated with fetal abnormalities and poor neonatal prognosis. The estimated incidence of persistent right umbilical vein in a low-risk population is 1 : 526. PMID 12047534
  • polyhydramnios - Clinical term for the accumulation of excess amniotic fluid during pregnancy. See also oligohydramnios, a deficiency of amniotic fluid.
  • placenta - (Greek, plakuos = flat cake) The developmental organ formed from maternal and fetal contributions in animals with placental development. In human, the placenta at term is a discoid shape "flat cake" shape; 20 cm diameter, 3 cm thick and weighs 500-600 gm. Placenta are classified by the number of layers between maternal and fetal blood (Haemochorial, Endotheliochorial and Epitheliochorial) and shape (Discoid, Zonary, Cotyledenary and Diffuse). The placenta has many different functions including metabolism, transport and endocrine.
  • placenta accreta - The abnormal placental adherence, either in whole or in part of the placenta with absence of decidua basalis, leading to retention as an after-birth to the underlying uterine wall. The incidence of placenta accreta also significantly increases in women with previous cesarean section compared to those without a prior surgical delivery.
  • placental arteries - (umbilical arteries) In placental animals, the blood vessels which develop within the placental cord carrying relatively deoxygenated blood from the embryo/fetus to the placenta. In humans, there are two placental arteries continuous with the paired internal iliac arteries (hypogastric arteries) arising off the dorsal aortas. At birth this vessel regresses and form the remnant medial umbilical ligament.
  • placental cord - (umbilical cord) The placental cord is the structure connecting the embryo/fetus to the placenta. It is initially extra-embryonic mesoderm forming the connecting stalk within which the placental blood vessels (arteries and veins) form. In human placental cords the placental blood vessels are initially paired, later in development only a single placental vein remains with a pair of placental arteries. This structure also contains the allantois, an extension from the hindgut cloaca then urogenital sinus. Blood collected from the placental cord following delivery is a source of cord blood stem cells.)
  • placental diameter - is measured in the transverse section by calculating the maximum dimensions of the chorionic surface.
  • placental growth factor - (PlGF) A growth factor of the vascular endothelial growth factor (VEGF) family, released from the placental trophoblast cells and other sources that stimulates blood vessel growth.
  • placental malaria - The malarial infection of the placenta by sequestration of the infected red blood cells. This condition can be common in regions where malaria is endemic with women carrying their first pregnancy (primigravida).
  • placenta membranacea - rare placental abnormality characterized by the presence of chorionic villi directly attached to and covering the fetal membranes. Placenta Membranacea
  • placenta previa - placenta overlies internal os of uterus, abnormal bleeding, may require cesarian delivery.
  • placental thickness - is measured at its mid-portion from the chorionic plate to the basilar plate, on a longitudinal plane (less than 4 cm at term). Excludes any abnormalities (fibroids, myometrial contractions, or venous lakes). The placental thickness approximates in millimeters to the weeks of gestation.
  • placental vein - (umbilical vein) In placental animals, the blood vessels which develop within the placental cord carrying relatively oxygenated blood from the placenta to the embryo/fetus. In humans, there are initially two placental veins which fuse to form a single vein. The resence of paired veins in the placental cord can be indicative of developmental abnormalities.
  • placentophagia - Term used to descrbe the maternal ingestion of afterbirth materials (placental membranes and amniotic fluid) that can occur following mammalian parturition (birth).
  • primary villi - (primary chorionic villi) Term describing the earliest stage of embryonic placenta development. In humans, the conceptus during week 2 this first stage of chorionic villi development consists of only the trophoblastic shell cells (syncitiotrophoblasts and cytotrophoblasts) forming finger-like extensions into maternal decidua. Initially these finger-like projections cover the entire surface of chorionic sac and later become restricted to the placental surface. The villi stages are ongoing as the placenta continues to grow through both the embryonic and fetal development.
  • pre-eclampsia - During pregnancy a combination of high blood pressure, protein in urine and fluid retention resulting in maternal sudden excessive swelling of the face, hands and feet. Eclampsia is the subsequent development of convulsions, kidney failure, liver failure, clotting problems or mortality.
  • Rh alloimmunization - feto-maternal haemorrhage generally in late pregnancy results in an Rh-negative woman becoming sensitised to Rh-positive fetal cells that enter her circulation. Clinically treated with anti-D immune globulin prophylaxis, alloimmunization occurs in 9–10% of at-risk pregnancies. immune
  • secondary villi - (secondary chorionic villi) Term describing the second stage of embryonic placenta development. In humans, the conceptus during week 3 onward this stage of chorionic villi development consists of the trophoblastic shell cells (syncytiotrophoblast and cytotrophoblasts) filled with extraembryonic mesoderm forming finger-like extensions into maternal decidua. Initially these finger-like projections cover the entire surface of chorionic sac and later become restricted to the placental surface. The villi stages are ongoing as the placenta continues to grow through both the embryonic and fetal development. Placental villi stages: primary villi - secondary villi - tertiary villi
  • syncytiotrophoblast - A multinucleated cell currently thought to form by the fusion of another trophoblast cell the cytotrophoblasts, within the trophoblast layer (shell) of the implanting conceptus. In early development, these cells mediate implantation of the conceptus into the uterine wall and secrete the hormone (Template:Human Chorionic Gonadotrophin, hCG) responsible for feedback maintainance of the corpus luteum (in maternal ovary) and therefore maintaining early pregnancy.
  • trophoblast - (trophectoderm, Greek, trophe = "nutrition" and blast = a primordial cell) cells that firstly support adplantation, implantation and endocrine support of pregnancy. Contribute to the extraembryonic tissues, fetal placenta and membranes. Initially form 2 populations individual cytotrophoblast cells and their fused multinucleate syncytiotrophoblast cells.
  • Twin-twin transfusion syndrome - (TTTS) in monozygotic twins with monochorionic and diamniotic placenta, with intrauterine blood transfusion from one twin (donor) to another twin (recipient) where there is an imbalance of blood flow from the donor twin to the recipient twin. Clinically diagnosed by the alternate presence of polyhydramnios in one fetus and oligohydramnios in the co-twin, occurs in about 10% of monochorionic twins.
  • umbilical cord (placental cord) fetal attachment cord 1-2 cm diameter, 30-90cm long, covered with amniotic attached to chorionic plate, umbilical vessels (artery, vein) branch into chorionic vessels. Vessels anastomose within the placenta.
  • umbilical vein varix - (fetal intra-abdominal umbilical vein varix, FIUV) focal dilatation of the umbilical venous diameter at the level of cord insertion, the dilatation diameter increases linearly with gestational age. Represent about 4% of umbilical cord abnormalities

with an incidence of about 2.8 per 1,000 pregnancies, there is also a rarer form of extra-abdominal varices. PMID 24883288

  • vasculogenesis - formation of first blood vessels by differentiation of pluripotent mesenchymal cells (extraembryonic mesoderm) followed by angiogenesis which is the development of new vessels from already existing vessels.
  • vasculosyncytial membranes - localised areas of the placental villous membrane where the barrier thickness separating maternal and fetal circulations is reduced to as little as 1-2 microns. PMID 1287078
  • villi - Plural of villus, which is a thin projection from a surface. The term in development is used to describe the individual functional units together of the fetal placenta.
  • virus - small infectious agents that may cross the placental barrier. Can infect embryo and/or placenta and cause developmental abnormalities. (e.g. cytomegalovirus, rubella, measles).
  • Wharton's jelly - placental cord (umbilical cord) gelatinous connective tissue composed of myofibroblast-like stromal cells, collagen fibers, and proteoglycans. Increases in volume (myxomatous, connective tissue embedded in mucus) at parturition (birth) to assist closure of placental blood vessels. Matrix cells from Wharton's jelly have recently been identified as a potential source of mesenchymal stem cells (MSC), also called mesenchymal stromal cell. This placental cord substance is named after Thomas Wharton (1614-1673) an English physician and anatomist who first described this placental tissue.
Other Terms Lists  
Terms Lists: ART | Birth | Bone | Cardiovascular | Cell Division | Endocrine | Gastrointestinal | Genital | Genetic | Head | Hearing | Heart | Immune | Integumentary | Neonatal | Neural | Oocyte | Palate | Placenta | Radiation | Renal | Respiratory | Spermatozoa | Statistics | Tooth | Ultrasound | Vision | Historic | Drugs | Glossary

Carnegie Stage 5

Historically this early implantation stage was divided into 3 separate sub-stages (a-c).

Stage 5a

Stage 5b

Stage 5c

Maternal Immune

How does the implanting conceptus avoid immune rejection by the maternal immune system? There are a number of maternal and embryonic mechanisms that are thought to act to prevent immune rejection of the implanting conceptus, though the complete mechanism(s) are unknown. This is particularly relevant to Assisted Reproductive Technologies involving donor eggs.

Below are some examples of research on this topic.

Decidual Immune Cells

Specialised immune cells.
Decidual Macrophages (Mϕ) Decidual T cells Uterine Natural Killer cells
  • regulatory role at the fetal-maternal interface.
  • M2 macrophage phenotype involved in tissue remodeling and inhibit inflammation
  • maintenance of tolerance to the non-self semi-allogeneic fetus
  • activated by fetal HLA-C (expressed on extravillous trophoblast cells)
  • specific immune tolerance to fetal alloantigens
  • Killer Inhibitory Receptor (KIR) activation by fetal HLA-C (expressed on extravillous trophoblast cells)

Chemokine Gene Silencing

Remove the attraction of maternal immune cells.

A mouse study[1] has shown that the normal immune response to inflammation, accumulation of effector T cells in response to chemokine secretion does not occur during implantation. This is prevented locally by epigenetic silencing of chemokine expression in the decidual stromal cells.

Corticotropin-Releasing Hormone

Kill the maternal immune cells.

Both maternal and implanting conceptus release CRH at the embryo implantation site. This hormone then binds to receptors on the surface of trophoblast (extravillous trophoblast) cells leading to expression of a protein (Fas ligand, FasL) that activates the extrinsic cell death pathway on any local maternal immune cells ( T and B lymphocytes, natural killer cells, monocytes and macrophages).[2] (Note - This cannot be the only mechanism, as mice with dysfunctional FasL proteins are still fertile).

Implantation - Monotocous/Polytocous

Polytocous animals produce many eggs or young at one time, compared to humans that mainly monotocous. ImplantaTion in polytocous animals (pig, mouse, rat) implanting blastocysts become evenly spaced along the uterus before embedding by an unexplained mechanism.


  1. Nancy P, Tagliani E, Tay CS, Asp P, Levy DE & Erlebacher A. (2012). Chemokine gene silencing in decidual stromal cells limits T cell access to the maternal-fetal interface. Science , 336, 1317-21. PMID: 22679098 DOI.
  2. Makrigiannakis A, Zoumakis E, Kalantaridou S, Coutifaris C, Margioris AN, Coukos G, Rice KC, Gravanis A & Chrousos GP. (2001). Corticotropin-releasing hormone promotes blastocyst implantation and early maternal tolerance. Nat. Immunol. , 2, 1018-24. PMID: 11590404 DOI.

11590404

BGDsmall.jpg
Practical 14: Implantation and Early Placentation | Villi Development | Maternal Decidua | Cord Development | Placental Functions | Diagnostic Techniques | Abnormalities