|Embryology - 24 Nov 2017 Expand to Translate|
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- 1 Introduction
- 2 Some Recent Findings
- 3 Reading
- 4 Placental Classification
- 5 Placental Villi Blood Vessels
- 6 Human Villi Timeline
- 7 Trophoblast Cells
- 8 Maternal Blood Flow
- 9 Term Placenta Measurements
- 10 Placental Factors
- 11 Placental Arteries and Vein
- 12 Placental Cord Histology
- 13 Placental Abnormalities
- 14 Comparative Placentation
- 15 References
- 16 Additional Images
- 17 Terms
- 18 External Links
- 19 Glossary Links
The placenta (Greek, plakuos = flat cake) named on the basis of this organs gross anatomical appearance. The placenta a mateno-fetal organ which begins developing at implantation of the blastocyst and is delivered with the fetus at birth. During that 9 month period it provides nutrition, gas exchange, waste removal, a source of hematopoietic stem cells, endocrine and immune support for the developing fetus.
There are essentially 3 separate aortic/venous circulatory systems: umbilical, systemic and vitelline. The umbilical system is lost at birth, the vitelline contributes to the portal system and the systemic (embryonic) is extensively remodelled to form the mature cardiovascular system.
Nutrition is derived from about 100–150 maternal uterine spiral arteries located in the basal plate and the human term placenta is about 9 cm in diameter.
2013 Meeting Presentation
Some Recent Findings
|More recent papers|
This table shows an automated computer PubMed search using the listed sub-heading term.
References listed on the rest of the content page and the associated discussion page (listed under the publication year sub-headings) do include some editorial selection based upon both relevance and availability.
Ting Tian, Zhenhai Yu, Naili Zhang, Yingwei Chang, Yuqiang Zhang, Luping Zhang, Shuai Zhou, Chunlei Zhang, Guoying Feng, Fei Huang Modified acellular nerve-delivering PMSCs improve functional recovery in rats after complete spinal cord transection. Biomater Sci: 2017; PubMed 29106428
Martin Gauster, Sabine Maninger, Monika Siwetz, Alexander Deutsch, Amin El-Heliebi, Dagmar Kolb-Lenz, Ursula Hiden, Gernot Desoye, Florian Herse, Andreas Prokesch Downregulation of p53 drives autophagy during human trophoblast differentiation. Cell. Mol. Life Sci.: 2017; PubMed 29080089
Amer Heider Fetal Vascular Malperfusion. Arch. Pathol. Lab. Med.: 2017, 141(11);1484-1489 PubMed 29072954
Hamutal Meiri, George Osol, Irene Cetin, Sveinbjörn Gizurarson, Berthold Huppertz Personalized Therapy Against Preeclampsia by Replenishing Placental Protein 13 (PP13) Targeted to Patients With Impaired PP13 Molecule or Function. Comput Struct Biotechnol J: 2017, 15;433-446 PubMed 29034064
D Fietz Transporter for sulfated steroid hormones in the testis - expression pattern, biological significance and implications for fertility in men and rodents. J. Steroid Biochem. Mol. Biol.: 2017; PubMed 29017936
- Human Embryology (2nd ed.) Larson Chapter 7 p151-188 Heart, Chapter 8 p189-228 Vasculature
- The Developing Human: Clinically Oriented Embryology (6th ed.) Moore and Persaud Chapter 14: p304-349
- Before we Are Born (5th ed.) Moore and Persaud Chapter 12; p241-254
- Essentials of Human Embryology Larson Chapter 7 p97-122 Heart, Chapter 8 p123-146 Vasculature
- Human Embryology Fitzgerald and Fitzgerald Chapter 13-17: p77-111
Classification of placenta is on the basis of histological (microscopic) structural organization and layers between fetal and maternal circulation.
Three main groups:
- Haemochorial - placenta where the chorion comes in direct contact with maternal blood (human).
- Endotheliochorial - maternal endometrial blood vessels are bare to their endothelium and these comes in contact with the chorion (dogs, cats).
- Epitheliochorial - maternal epithelium of the uterus comes in contact with the chorion, considered as primitive (pigs, cows).
The presence of these three differing types of placenta have also been used to describe the pattern mammalian evolution.
|Postnatal Animal Models||Mouse||Rat||Pig|
|Pregnancy period (days)||18 – 21||21 – 23||110 – 118|
|Placenta type|| Discoidal, decidual
| Discoidal, decidual
|Litter size||6 – 12||6 – 15||11 – 16|
|Birth weight (g)||0.5 – 1.5||3 – 5||900 – 1600|
|Weaning weight male/female (g)||18 – 25/16 – 25||55 – 90/45 – 80||6000 – 8000|
|Suckling period (days)||21–28||21||28–49|
|Solid diet beginning (days)||10||12||12 – 15|
|Puberty male/female (week)||4 – 6/5||6/6 – 8||20 – 28|
|Life expectancy (years)||1 - 2||2 - 3||14 – 18|
Placenta MRI (37 weeks) Placenta located at the upper segment of uterus.
Placental Villi Blood Vessels
Some of the following data is from a histological study of human placental villi.
- macrophage-like cells first cells to differentiate at day 21 (post-conception) from mesenchymal precursors.
- haemangioblastic cell cords (angiogenic cell cords, ACC) at day 21 (post-conception) also from mesenchymal cells, are the precursors of the capillary endothelium and haematopoietic stem cells
- pericytes form later and are a third cell population derived from the mesenchymal cells
- first main vascular patterns grow towards the longitudinal axis of the developing villi
- capillary basal lamina cannot be detected earlier than in the third trimester
- third trimester - fetal villous angiogenesis occurs by proliferation of the existing endothelium and pericytes rather than through haemangioblastic cells.
Human Villi Timeline
The placental vill development data below is based upon a recent immunochemistry confocal laser scanning microscope (CLSM) study.
Note that the paper uses clinical gestational age (GA) from last menstrual period (LMP) and has been corrected for post-conception (fertilization) age, approximately 14 days later.
|Vessel Lumen Diameter
(range in microns)
|3 to 4||5 and 6||10 - 15||
|5 to 6||7 and 8||10 - 26||
|7 to 8||9 and 10|| 60 - 75 two central vessels
26 - 34 capillary network
|9 to 10||11 and 12|| 70 - 90 two central vessels
26 - 34 capillary network
|Term|| Terminal villi
CD31 - (PECAM-1, Platelet Endothelial Cell Adhesion Molecule) is a cluster of differentiation molecule found on endothelial and other blood cells.
Following implantation the initial trophoblast cells can differentiate into 2 pathways:
- Extravillous - cytotrophoblastic cells proliferate and differentiate into an invasive phenotype that invade (interstitial trophoblast) the maternal decidual stroma and the spiral arteries (endovascular trophoblast) of the myometrium.
- Villous - cytotrophoblastic cells proliferate and fuse to form the multi-nucleated syncytiotrophoblast cells that form the outer surface of the fetal placental villi.
Maternal Blood Flow
Maternal blood pressure normally decreases or remains unchanged during pregnancy while both cardiac output and vascular volume are increased. Uterine blood flow changes are principally due to a decrease in uterine vascular resistance. There is also an associated structural enlargement of both the uterine arterial and venous trees, reduced vascular tone (vasodilation) and placenta development.
Uteroplacental blood flow (UPBF) was historically measured by a number of different mathematical calculations and probe methods, currently the method involves transvaginal doppler ultrasonography.
In human singleton pregnancies, uteroplacental blood flow (UPBF) begins at 20–50 ml/min and increases (linearly) to 450–800 ml/min, with twin pregnancy values in excess of 1 l/min.
Uterine Artery Diameter
The following data is from a study of 18 pregnant women using ultrasound and doppler analysis of the uterine artery.
- GA week 21 doubled (from 1.4 to 2.8 mm).
- GA week 21 to 30 remained constant (2.9mm).
- GA week 30 to 36 increased (to 3.4 mm).
Uterine artery mean flow velocity also increased nearly eight times from non-pregnant (8.4 cm/second) to GA week 36 (61.4 cm/second).
Arcuate and Radial Arteries
These branches from the paired uterine arteries also remodel enlarging in lumen diameter between 25 to 220% with either no change or an increase in wall thickness. Arcuate arteries also elongate either by longitudinal growth or by the progressive straightening of these coiled vessels.
Term Placenta Measurements
There are a variety of diagnostic and morphological measurements that can be made of the placenta during pregnancy and at term.
Simple measurements of overall placental diameter, thickness and volume:
- placental diameter - is measured in the transverse section by calculating the maximum dimensions of the chorionic surface.
- 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 volume - is measured by a range of different methods and calculations, more recently with three-dimensional ultrasound.
Detailed morphometric indices at term of placental composition, villous capillarization and the mean cross-sectional areas of peripheral villi and capillaries, data from a study sample of 15 normal placenta (mean placental volume, 652 ml). 
|Variable||Unit||Placenta (mean, n = 15)|
|TS area villi||µm2||3700|
|TS area capillary||µm2||150|
|Length ratio||km km-1||3.6|
As the placenta develops it becomes the source of many different factors (hormones, growth factors) and also has the ability to metabolise both maternal and fetal factors.
Placental Growth Factor
(PGF, 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. See review.
Insulin/insulin-like Growth Factor
- IGF1 and IGF2 are both synthesized in the placenta and the fetus.
- IGF1 present in syncytiotrophoblast and cytotrophoblast at all stages.
- IGF2 not found in the syncytiotrophoblasts.
- IGF2 expression in the villous and extravillous cytotrophoblasts in the first trimester becomes undetectable at term.
Placental Arteries and Vein
Placental Cord Histology
Note there is also a specific page covering the topic of placental abnormalities.
- Placenta Accreta - abnormal adherence, with absence of decidua basalis. The incidence of placenta accreta also significantly increases in women with previous cesarean section compared to those without a prior surgical delivery.
- Placenta Increta - occurs when the placenta attaches deep into the uterine wall and penetrates into the uterine muscle, but does not penetrate the uterine serosa. Placenta increta accounts for approximately 15-17% of all cases.
- Placenta Percreta - placental villi penetrate myometrium and through to uterine serosa.
- Placenta Previa - In this placenatal abnormality, the placenta overlies internal os of uterus, essentially covering the birth canal. This condition occurs in approximately 1 in 200 to 250 pregnancies. In the third trimester and at term, abnormal bleeding can require cesarian delivery and can also lead to Abruptio Placenta. Ultrasound screening programs during 1st and early 2nd trimester pregnancies now include placental localization. Diagnosis can also be made by transvaginal ultrasound.
- Vasa Previa - (vasa praevia) placental abnormality where the fetal vessels lie within the membranes close too or crossing the inner cervical os (opening). This occurs normally in 1:2500-5000 pregnancies and leads to complications similar too those for Placenta Previa.Type II is defined as the condition where the fetal vessels are found crossing over the internal os connecting either a bilobed placenta or a succenturiate lobe with the main placental mass. Some recent evidence of successful in utero laser ablation of type II vasa previa at 22.5 weeks of gestation.
- Abruptio Placenta - a retroplacental blood clot formation, abnormal hemorrhage prior to delivery.
- Chronic Intervillositis - (massive chronic intervillositis, chronic histiocytic intervillositis) Rare placental abnormality and pathology defined by inflammatory placental lesions, mainly in the intervillous space (IVS), with a maternal infiltrate of mononuclear cells (monocytes, lymphocytes, histiocytes) and intervillous fibrinoid deposition.
- Hydatidiform mole - placental tumor with no embryo development. Several forms of hydatidiform mole: partial mole, complete mole and persistent gestational trophoblastic tumor. Many of these tumours arise from a haploid sperm fertilizing an egg without a female pronucleus (the alternative form, an embryo without sperm contribution, is called parthenogenesis). The tumour has a "grape-like" placental appearance without enclosed embryo formation. Following a first molar pregnancy, there is approximately a 1% risk of a second molar pregnancy.
- Links: Placenta - Abnormalities
Placental Cord Abnormalities
There are few abnormalities associated with umbilical cord development, other that abnormally short or long cords, which in most cases do not cause difficulties. In some cases though, long cords can wrap around limbs or the fetus neck, which can then restrict blood flow or lead to tissue or nerve damage, and therefore effect develoment.
- Cord knotting - can also occur (1%) in most cases these knots have no effect, in some cases of severe knotting this can prevents the passage of placental blood.
- Cord torsion - Rare event where even without knot formation can also affect placental blood flow, even leading to fetal demise.
- Links: Placenta Cord Development | Placenta - Abnormalities | WebPath - umbilical cord knot 1 | WebPath - umbilical cord knot 2 | WebPath - Pseudoknot of umbilical cord, gross | WebPath - Torsion of umbilical cord, gross | WebPath - Torsion of umbilical cord, with fetal demise, gross
- Several infective agents may cross into the placenta from the maternal circulation, as well as enter the embry/fetal circulation. The variety of bacterial infections that can occur during pregnancy is as variable as the potential developmental effects, from virtually insignificant to a major developmental, abortive or fatal in outcome.
- Pregnant women have an increased susceptibility to malaria infection. Malarial infection of the placenta by sequestration of the infected red blood cells leading to low birth weight and other effects. There are four types of malaria caused by the protozoan parasite Plasmodium falciparum (main), Plasmodium vivax, Plasmodium ovale, Plasmodium malariae). This condition is common in regions where malaria is endemic with women carrying their first pregnancy (primigravida).
- Chronic Villitis - can occur following placental infection leading to maternal inflammation of the villous stroma, often with associated intervillositis. The inflammation can lead to disruption of blood flow and necrotic cell death.
- Massive Chronic Intervillositis (MCI) - maternal blood-filled space is filled with CD68-positive histiocytes and an increase in fibrin, occuring more commonly in the first trimester.
- Meconium Myonecrosis - prolonged meconium exposure leads to toxic death of myocytes of placental vessels (umbilical cord or chorionic plate).
- Neuroblastoma - a fetal malignancy that leads to an enlarged placenta, with tumor cells in the fetal circulation and rarely in the chorionic villi.
- Thrombophilias - (protein C or S deficiency, factor V Leiden, sickle cell disease, antiphospholipid antibody) can generate an increased fibrin/fibrinoid deposition in the maternal or intervillous space, this can trap and kill villi.
The Comparative Placentation website has been available online for many years providing valuable information about placentation in a wide range of species. The site was developed by Dr Kurt Benirschke, a longstanding expert in the field. Dr Kurt Benirschke retired in 1994 and continued to develop and maintain the website (that is still available) until 2012, but it has not been updated since that time.
- Martina Scotti, Marie Kmita Recruitment of 5' Hoxa genes in the allantois is essential for proper extra-embryonic function in placental mammals. Development: 2012, 139(4);731-9 PubMed 22219351
- Alexandre Bonnin, Nick Goeden, Kevin Chen, Melissa L Wilson, Jennifer King, Jean C Shih, Randy D Blakely, Evan S Deneris, Pat Levitt A transient placental source of serotonin for the fetal forebrain. Nature: 2011, 472(7343);347-50 PubMed 21512572
- Brian Cox, Max Kotlyar, Andreas I Evangelou, Vladimir Ignatchenko, Alex Ignatchenko, Kathie Whiteley, Igor Jurisica, S Lee Adamson, Janet Rossant, Thomas Kislinger Comparative systems biology of human and mouse as a tool to guide the modeling of human placental pathology. Mol. Syst. Biol.: 2009, 5;279 PubMed 19536202
- Anthony M Carter, Allen C Enders Comparative aspects of trophoblast development and placentation. Reprod. Biol. Endocrinol.: 2004, 2;46 PubMed 15236656 | Reprod Biol Endocrinol.
- Binoj Varghese, Navdeep Singh, Regi A N George, Sareena Gilvaz Magnetic resonance imaging of placenta accreta. Indian J Radiol Imaging: 2013, 23(4);379-85 PubMed 24604945 | PMC3932583 | Indian J Radiol Imaging.
- Joanne Hempstock, Tereza Cindrova-Davies, Eric Jauniaux, Graham J Burton Endometrial glands as a source of nutrients, growth factors and cytokines during the first trimester of human pregnancy: a morphological and immunohistochemical study. Reprod. Biol. Endocrinol.: 2004, 2;58 PubMed 15265238 | Reprod. Biol. Endocrinol.
- R Demir, P Kaufmann, M Castellucci, T Erbengi, A Kotowski Fetal vasculogenesis and angiogenesis in human placental villi. Acta Anat (Basel): 1989, 136(3);190-203 PubMed 2481376
- B A M Lisman, M J B van den Hoff, K Boer, O P Bleker, K van Groningen, N Exalto The architecture of first trimester chorionic villous vascularization: a confocal laser scanning microscopical study. Hum. Reprod.: 2007, 22(8);2254-60 PubMed 17545656
- George Osol, Maurizio Mandala Maternal uterine vascular remodeling during pregnancy. Physiology (Bethesda): 2009, 24;58-71 PubMed 19196652
- S K Palmer, S Zamudio, C Coffin, S Parker, E Stamm, L G Moore Quantitative estimation of human uterine artery blood flow and pelvic blood flow redistribution in pregnancy. Obstet Gynecol: 1992, 80(6);1000-6 PubMed 1448242
- T M Mayhew, H Jenkins, B Todd, V L Clifton Maternal asthma and placental morphometry: effects of severity, treatment and fetal sex. Placenta: 2008, 29(4);366-73 PubMed 18328557
- Terry M Mayhew A stereological perspective on placental morphology in normal and complicated pregnancies. J. Anat.: 2009, 215(1);77-90 PubMed 19141109
- Sandro De Falco The discovery of placenta growth factor and its biological activity. Exp. Mol. Med.: 2012, 44(1);1-9 PubMed 22228176 | PDF
- K Benirschke Remarkable placenta. Clin Anat: 1998, 11(3);194-205 PubMed 9579593
- Kurt Benirschke Placentas, peccaries, and pathologists: reminiscences of Kurt Benirschke on his career: an interview with Rebecca N. Baergen. Int. J. Gynecol. Pathol.: 2002, 21(3);289-300 PubMed 12068178
Kirsten Ferner, Andrea Mess Evolution and development of fetal membranes and placentation in amniote vertebrates. Respir Physiol Neurobiol: 2011, 178(1);39-50 PubMed 21470579
G Riquelme Review: Placental syncytiotrophoblast membranes--domains, subdomains and microdomains. Placenta: 2011, 32 Suppl 2;S196-202 PubMed 21272934
Judith E Cartwright, Rupsha Fraser, Karin Leslie, Alison E Wallace, Joanna L James Remodelling at the maternal-fetal interface: relevance to human pregnancy disorders. Reproduction: 2010, 140(6);803-13 PubMed 20837731
Wang Y, Zhao S. Vascular Biology of the Placenta. San Rafael (CA): Morgan & Claypool Life Sciences; 2010. Bookshelf NBK53247
C M Salafia, M Yampolsky, D P Misra, O Shlakhter, D Haas, B Eucker, J Thorp Placental surface shape, function, and effects of maternal and fetal vascular pathology. Placenta: 2010, 31(11);958-62 PubMed 20933281
J F Yetter Examination of the placenta. Am Fam Physician: 1998, 57(5);1045-54 PubMed 9518951
- Wang Y, Zhao S. Vascular Biology of the Placenta. San Rafael (CA): Morgan & Claypool Life Sciences; 2010. Available from: http://www.ncbi.nlm.nih.gov/books/NBK53247
- Boyd, J.D., Hamilton, W.J. 1970. The utero-placental circulatory system. In: The Human Placenta. W Heffer and Sons Ltd, London.
Historic Textbooks and Research
- The Elements of Embryology (1883)
- Atlas of the Development of Man Volume 1 (1907)
- Manual of Human Embryology (1910)
- Manual of Human Embryology (1917) (unedited)
- Text-Book of Embryology (1921) | The Foetal Membranes in Man
- Contributions to Embryology No.64 Cyclic changes in the ovaries and uterus of swine, and their relations to the mechanism of implantation. George W. Corner.
Search April 2010
- Placenta Development - All (10032) Review (1896) Free Full Text (2435)
- Placental Development - All (9103) Review (1762) Free Full Text (2219)
- Placental Membranes - All (10083) Review (748) Free Full Text (1728)
|Historic Disclaimer - information about historic embryology pages|
|Embryology History | Historic Embryology Papers)|
| Gray H. Anatomy of the human body. (1918) Philadelphia: Lea & Febiger.
| Bailey FR. and Miller AM. Text-Book of Embryology (1921) New York: William Wood and Co.
|Placenta Terms (expand to view)|
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External Links Notice - The dynamic nature of the internet may mean that some of these listed links may no longer function. If the link no longer works search the web with the link text or name. Links to any external commercial sites are provided for information purposes only and should never be considered an endorsement. UNSW Embryology is provided as an educational resource with no clinical information or commercial affiliation.
- Comparative Placentation homepage | index | glossary
- The Human Placenta Project - a collaborative research effort, launched by the NICHD to understand the role of the placenta in health and disease.Human Placenta Project | Video
- International Federation of Placenta Associations IFPA Meetings | 2011 IFPA Meeting, Geilo, Norway
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Cite this page: Hill, M.A. 2017 Embryology Placenta Development. Retrieved November 24, 2017, from https://embryology.med.unsw.edu.au/embryology/index.php/Placenta_Development
- © Dr Mark Hill 2017, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G