Welcome to The Visible Embryo



Home-- -History-- -Bibliography- -Pregnancy Timeline- --Prescription Drugs in Pregnancy- -- Pregnancy Calculator- --Female Reproductive System- -Contact

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

Pregnancy Calculator

Female Reproductive System

Contact The Visible Embryo

News Alerts Archive

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.
Content protected under a Creative Commons License.

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 27, 2014


Crawling C. elegans by Bob Goldstein

WHO Child Growth Charts




How nerves tell top from bottom - front from back

Neurons and axons have polarity which gives them direction in the body. Positioning is fundamental to any organism. All cellular structures must be precisely oriented in order to work accurately.

To better understand how neuron and axon migration work, lead author Naomi Levy-Strumpf, PhD along with principal investigator Joseph Culotti, PhD investigated the netrin and Wnt signaling pathways in the humble worm C. elegans. Caenorhabditis elegans, or C. elegans, is a transparent, non-parasitic roundworm about 1 mm in length that lives in soil. As of 2012, it is the only organism to have its "wiring" completely genetically diagrammed.

Within the cytoplasm of cells, proteins emit signals which either attract or repel other proteins.

Levy-Strumpf and Culotti chose to examine the UNC-6/netrin system as each part of this system was known for its affect on migration. UNC-6/netrin emits an attract signal guiding cell migration along a middle axis (dorso-ventral or D/V). In a human D/V would indicate the path from our back to our belly. Meanwhile, the Wnts protein pathways are critical for determining polarity and guidance along a head to toe axis (antero-posterior or A/P).

The researchers unexpected finding is that UNC-6/netrin and Wnts pathway emit both A/P and D/V signals. This redundant behavior probably functions to increase the reliability of both systems. This is a new concept in how A/P and D/V guidance generates cell migration.

"This redundancy tends to mask the roles of netrin and Wnt signaling in various biological processes. Now that we have identified their redundancy - we have better insight into how these two key signalling pathways contribute in normal development as well as to tumor progression and metastasis."

Naomi Levy-Strumpf, PhD, research associate, Culotti lab, Department of Molecular Genetics, University of Toronto, Ontario, Canada

'In addition to providing polarity information for migration along the axis of their gradation, Wnts and netrin are each able to guide migrations orthogonal [lying at right angles] to the axis of their gradation. These results suggest the existence of novel mechanisms for guiding cell migrations that are different from previously demonstrated mechanisms involving simple attraction toward or repulsion away from a guidance cue."

Joseph Culotti, PhD, principal investigator, Lunenfeld-Tanenbaum Research Institute of Mount Sinai Hospital, Toronto, Ontario, Canada, Department of Molecular Genetics, University of Toronto, Ontario, Canada

"This is an excellent example of the power of genetic analysis of the worm in neurobiology," says Dr. Jim Woodgett, Director of the Lunenfeld-Tanenbaum. "Now that this pathway interaction has been shown to occur, it'll only be a matter of time for someone to replicate it in mice."

The work is published in the journal PLoS GENETICs.

Guided migrations of cells and developing axons along the dorso-ventral (D/V) and antero-posterior (A/P) body axes govern tissue patterning and neuronal connections. In C. elegans, as in vertebrates, D/V and A/P graded distributions of UNC-6/Netrin and Wnts, respectively, provide instructive polarity information to guide cells and axons migrating along these axes. By means of a comprehensive genetic analysis, we found that simultaneous loss of Wnt and Netrin signaling components reveals previously unknown and unexpected redundant roles for Wnt and Netrin signaling pathways in both D/V and A/P guidance of migrating cells and axons in C. elegans, as well as in processes essential for organ function and viability. Thus, in addition to providing polarity information for migration along the axis of their gradation, Wnts and Netrin are each able to guide migrations orthogonal to the axis of their gradation. Netrin signaling not only functions redundantly with some Wnts, but also counterbalances the effects of others to guide A/P migrations, while the involvement of Wnt signaling in D/V guidance identifies Wnt signaling as one of the long sought mechanisms that functions in parallel to Netrin signaling to promote D/V guidance of cells and axons. These findings provide new avenues for deciphering how A/P and D/V guidance signals are integrated within the cell to establish polarity in multiple biological processes, and implicate broader roles for Netrin and Wnt signaling - roles that are currently masked due to prevalent redundancy.

This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Funding was provided by the Canadian Institutes for Health Research, Canadian Foundation for Innovation, Canada Research Chairs, and Mount Sinai Hospital Foundation.

Return to top of page