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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.

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The World Health Organization (WHO) has created a new Web site to help researchers, doctors and
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Pregnancy Timeline by SemestersLungs begin to produce surfactantImmune system beginningHead may position into pelvisFull TermPeriod of rapid brain growthWhite fat begins to be madeHead may position into pelvisWhite fat begins to be madeImmune system beginningBrain convolutions beginBrain convolutions beginFetal liver is producing blood cellsSensory 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 Mar 11, 2015

Taste cells regenerate about every 10 days, almost as frequently as skin cells.
Taste preferences and aversions can be modified before birth based on mom's diet.




Developing a sense of taste

Our sense of taste is actually a combination of smell, taste and texture. A single taste bud can have dozens of receptor cells sending signals of sour, sweet, salty and bitter through nerve pathways to our brain. Taste even plays a role in digestion, preparing the stomach for a meal. But more significantly, taste cells regenerate every 10 days.

Our tongue is covered with taste buds allerting us to the quality and safety of our food, for example the back of our mouth is sensitive to bitter — perhaps in a last-ditch effort to have us expel anything toxic. But one of the most interesting things about taste, according to University of Virginia neuroscientist David Hill, is that taste cells regenerate about every 10 days, almost as frequently as skin cells.

"Brain cells generally don't regenerate, which is why Alzheimer's is so devastating," said Hill, who is a U.Va. psychology professor and department chair. "However ...understanding the way neurons regenerate may come from studies of our olfactory system. Olfactory receptor neurons are constantly dying and being replaced."

Hill operates one of only a handful of laboratories worldwide studying the development of the taste system - the least studied of our five senses. In contrast, vision and hearing are studied much more commonly and thoroughly in hundreds of labs. Hill has published numerous studies on taste, including a January 7, 2015 finding on the mouse taste system in The Journal of Neuroscience.

Hill admits there are no devastating diseases directly associated with taste. "I need to be able to see and hear, to smell and feel, but I could do without my sense of taste, if I had to. But as a neuroscientist, I've chosen to study taste because we...can learn a great deal about all the senses and the development of the nervous system by studying the many interesting facets of taste."

Using mice as models, Hill is looking at how huge changes occur in neurodevelopment in the womb, depending on the diet of the mother during pregnancy.

"One of our questions is, 'If taste cells are constantly turning over, how does the nervous system keep reliable information coming to the brain when the reception system is always in flux? We want to understand how our wiring changes in early development and adulthood," Hill said.

Hill's findings demonstrate the importance of diet in pre-natal development. He has shown that our taste system is highly malleable, and taste preferences and aversions can be modified prior to birth and throughout life based on changes in diet.

Animals actively acquire sensory information from the outside world, with rodents sniffing to smell and whisking to feel. Licking, a rapid motor sequence used for gustation, serves as the primary means of controlling stimulus access to taste receptors in the mouth. Using a novel taste-quality discrimination task in head-restrained mice, we measured and compared reaction times to four basic taste qualities (salt, sour, sweet, and bitter) and found that certain taste qualities are perceived inherently faster than others, driven by the precise biomechanics of licking and functional organization of the peripheral gustatory system. The minimum time required for accurate perception was strongly dependent on taste quality, ranging from the sensory-motor limits of a single lick (salt, ~100 ms) to several sampling cycles (bitter, >500 ms). Further, disruption of sensory input from the anterior tongue significantly impaired the speed of perception of some taste qualities, with little effect on others. Overall, our results show that active sensing may play an important role in shaping the timing of taste-quality representations and perception in the gustatory system.

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