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Welcome to The Visible Embryo, a comprehensive educational resource on human development from conception to birth.

The Visible Embryo provides visual references for changes in fetal development throughout pregnancy and can be navigated via fetal development or maternal changes.

The National Institutes of Child Health and Human Development awarded Phase I and Phase II Small Business Innovative Research Grants to develop The Visible Embryo. Initally designed to evaluate the internet as a teaching tool for first year medical students, The Visible Embryo is linked to over 600 educational institutions and is viewed by more than one million visitors each month.

Today, The Visible Embryo is linked to over 600 educational institutions and is viewed by more than 1 million visitors each month. The field of early embryology has grown to include the identification of the stem cell as not only critical to organogenesis in the embryo, but equally critical to organ function and repair in the adult human. The identification and understanding of genetic malfunction, inflammatory responses, and the progression in chronic disease, begins with a grounding in primary cellular and systemic functions manifested in the study of the early embryo.

WHO International Clinical Trials Registry Platform

The World Health Organization (WHO) has created a new Web site to help researchers, doctors and
patients obtain reliable information on high-quality clinical trials. Now you can go to one website and search all registers to identify clinical trial research underway around the world!




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Pregnancy Timeline by SemestersFetal liver is producing blood cellsHead may position into pelvisBrain convolutions beginFull TermWhite fat begins to be madeWhite fat begins to be madeHead may position into pelvisImmune system beginningImmune system beginningPeriod of rapid brain growthBrain convolutions beginLungs begin to produce surfactantSensory brain waves begin to activateSensory brain waves begin to activateInner Ear Bones HardenBone marrow starts making blood cellsBone marrow starts making blood cellsBrown fat surrounds lymphatic systemFetal sexual organs visibleFinger and toe prints appearFinger and toe prints appearHeartbeat can be detectedHeartbeat can be detectedBasic Brain Structure in PlaceThe Appearance of SomitesFirst Detectable Brain WavesA Four Chambered HeartBeginning Cerebral HemispheresFemale Reproductive SystemEnd of Embryonic PeriodEnd of Embryonic PeriodFirst Thin Layer of Skin AppearsThird TrimesterSecond TrimesterFirst TrimesterFertilizationDevelopmental Timeline
CLICK ON weeks 0 - 40 and follow along every 2 weeks of fetal development
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Home | Pregnancy Timeline | News Alerts |News Archive Jan 24, 2014


Above, 3 day old zebrafish larva.
Green Flourescent Protein (GFP) is expressed in the liver (Top)
folowing exposure to an estrogen like chemical.
An unexposed response was also found in the developing
heart valves (Left) open valve state and (Right) closed valve state.

WHO Child Growth Charts




Developing heart valves sensitive to bisphenol A

Exposure to environmental endocrine disrupters — such as bisphenol A or BPA — mimic estrogen and are associated with adverse health effects. BPA is commonly found in plastic bottles and plastic food containers.

New research from Daniel Gorelick and Marnie Halpern of the Carnegie Institute of Sciences, followed the effects of endocrine disrupters on zebrafish and found that embryonic heart valves are particularly at danger of malformation. Gorelick, lead author, Halpern and Alice Hung, along with Luke Iwanowicz and Vicki Blazer of the Fish Health Branch of the U.S. Geological Survey, used genetically modified zebrafish to show estrogen receptor activity on a cell's DNA.

Their findings indicate that these specially developed zebrafish are not only great tools for detecting environmental endocrine disruptors in river water, but also for identifying which tissues are being targeted by these disruptors.

It was unexpected that estrogen receptors in developing heart valves would be activated by river water samples as it was unseen in previous experiments. This observation raises interesting questions about the role of estrogen in valve formation and whether other environmental chemicals can contribute to valve abnormalities.

The work is published in Environmental Health Perspectives.

Estrogen hormones are important in all stages of life. They work by binding to receptors inside a cell, which then travel to the nucleus and promote the DNA to turn select genes on or off.

But some synthetic chemicals mimic these estrogen hormones by also binding to gene receptors. Exposure to these chemicals during early development is associated with increased risk of cancers and abnormal formation of the reproductive tract. So the ability to detect such chemicals and identify their mechanisms of action is of great importance for developmental science.

Background: Environmental endocrine disruptors (EED) are exogenous chemicals that mimic endogenous hormones, such as estrogens. Previous studies using a zebrafish transgenic reporter demonstrated that the EEDs bisphenol A and genistein preferentially activate estrogen receptors (ER) in the larval heart compared to the liver. However, it was not known whether the transgenic zebrafish reporter was sensitive enough to detect estrogens from environmental samples, whether environmental estrogens would exhibit similar tissue-specific effects as BPA and genistein or why some compounds preferentially target receptors in the heart.

Methods: We tested surface water samples using a transgenic zebrafish reporter with tandem estrogen response elements driving green fluorescent protein expression (5xERE:GFP). Reporter activation was colocalized with tissue-specific expression of estrogen receptor genes by RNA in situ hybridization.

Results: Selective patterns of ER activation were observed in transgenic fish exposed to river water samples from the Mid-Atlantic United States, with several samples preferentially activating receptors in embryonic and larval heart valves. We discovered that tissue-specificity in ER activation is due to differences in the expression of estrogen receptor subtypes. ERα is expressed in developing heart valves but not in the liver, whereas ERβ2 has the opposite profile. Accordingly, subtype-specific ER agonists activate the reporter in either the heart valves or the liver.

Conclusion: The use of 5xERE:GFP transgenic zebrafish has revealed an unexpected tissue-specific difference in the response to environmentally relevant estrogenic compounds. Exposure to estrogenic EEDs in utero is associated with adverse health effects, with the potentially unanticipated consequence of targeting developing heart valves.

This work was supported by the National Institutes of Health National Research Service Award Postdoctoral Fellowship from the Eunice Kennedy Shriver National Institute of Child Health and Human Development and the USGS Chesapeake Bay Priority Ecosystems program.

The Carnegie Institution for Science is a private, nonprofit organization headquartered in Washington, D.C., with six research departments throughout the U.S. Since its founding in 1902, the Carnegie Institution has been a pioneering force in basic scientific research. Carnegie scientists are leaders in plant biology, developmental biology, astronomy, materials science, global ecology, and Earth and planetary science.