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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!




Pregnancy Timeline

Prescription Drug Effects on Pregnancy

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Female Reproductive System

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Disclaimer: The Visible Embryo web site is provided for your general information only. The information contained on this site should not be treated as a substitute for medical, legal or other professional advice. Neither is The Visible Embryo responsible or liable for the contents of any websites of third parties which are listed on this site.
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No dirivative works may be made or used for commercial purposes.


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
Google Search artcles published since 2007

Home | Pregnancy Timeline | News Alerts |News Archive June 10, 2014


About four days after the sperm merges with the egg, a cavity known as a blastocele
forms in the center of the early embryo. Cells flatten and compact on the inside
of the blastocele cavity, while the outer shell (zona pellucida) still surrounds
the floating embryo. The appearance of the cavity in the center of the egg changes
the structure into what is now called a blastocyst. The blastocyst indicates that
two cell types are forming: the embryoblast (inner cell mass on the inside),
and the trophoblast (the cells on the outside). The expanding cells break free
from the zona as the early embryo begins to burrow into the uterine wall.


WHO Child Growth Charts




First steps to stem cells becomming 3 fetal cell layers

A research team has found the precise combination of mechanical forces, chemistry and timing to help stem cells differentiate into three germ layers, the first step towards developing specialized tissues and organs of a fetus.

The gap between stem cell research and regenerative medicine just became a lot narrower. A new technique coaxes stem cells, which have the potential to become any tissue type, to take the first step into specialization. It is the first time this critical step has been demonstrated in a laboratory.

University of Illinois researchers, in collaboration with scientists at Notre Dame University and the Huazhong University of Science and Technology in China, published their results in the journal Nature Communications.

“Everybody knows that for an embryo to form, somehow a single cell has a way to self-organize into multiple cells, but the in vivo microenvironment is not well understood,” said study leader Ning Wang, a professor of mechanical science and engineering at the U. of I. “We want to know how they develop into organized structures and organs. It doesn’t happen by random chance. There are biological rules that we don’t yet understand.”

During fetal development, all the specialized tissues and organs of the body form out of a small ball of stem cells.

First, the ball of generalized cells separates into three different cell lines, called germ layers, which will become different systems of the body.

This crucial first step has eluded researchers in the lab. No one has yet been able to induce the cells to form the three distinct germ layers, in the correct order – endoderm on the inside, mesoderm in the middle and ectoderm on the outside.

This represents a major hurdle in the application of stem cells to regenerative medicine, since researchers need to understand how tissues develop before they can reliably recreate the process.

“It’s very hard to generate tissues or organs, and the reason is that we don’t know how they form in vivo,” says Wang. “The problem, fundamentally, is that the biological process is not clear. What is the biological environment that controls this process making stem cells become more organized and specialized?”

Wang’s team demonstrated that not only is it possible for mouse embryonic stem cells to form three distinct germ layers in the lab, but also that achieving the separation requires a careful combination of the timing of chemical factors with the help of a mechanical environment. The team used cell lines that fluoresce in different colors when they become part of a germ layer, which allowed the researchers to monitor the process dynamically.

They first deposited the stem cells in a very soft gel matrix, attempting to recreate one of the properties of the womb. They found several mechanical forces had an affect on how the cells organized and differentiated – the stiffness of the gel, the force each cell exerts on its neighbors, and the matrix of proteins that cells deposit internally as scaffolding within the developing embryo.

By adjusting these mechanical elements, the researchers were able to observe how each force affected the dividing cells, and found one particular combination that yielded three germ layers. They were even able to change these elements causing the layers to form in reverse order.

Now, Wang’s group is working to improve their technique for greater efficiency. He hopes that other researchers will be able to use the technique to bridge the gap between stem cells and tissue engineering.

“It’s the first time we’ve had the correct three-germ-layer organization in mammalian cells,” Wang said. “The potential is huge. Now we can push it even further and generate specific organs and tissues. It opens the door for regenerative medicine.”

Mammalian inner cell mass cells undergo lineage-specific differentiation into germ layers of endoderm, mesoderm and ectoderm during gastrulation. It has been a long-standing challenge in developmental biology to replicate these organized germ layer patterns in culture. Here we present a method of generating organized germ layers from a single mouse embryonic stem cell cultured in a soft fibrin matrix. Spatial organization of germ layers is regulated by cortical tension of the colony, matrix dimensionality and softness, and cell–cell adhesion. Remarkably, anchorage of the embryoid colony from the 3D matrix to collagen-1-coated 2D substrates of ~1 kPa results in self-organization of all three germ layers: ectoderm on the outside layer, mesoderm in the middle and endoderm at the centre of the colony, reminiscent of generalized gastrulating chordate embryos. These results suggest that mechanical forces via cell–matrix and cell–cell interactions are crucial in spatial organization of germ layers during mammalian gastrulation. This new in vitro method could be used to gain insights on the mechanisms responsible for the regulation of germ layer formation.

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