be careful where you clique
One of the most captivating subjects in all Medical School is First Year Embryology. It’s the subject you keep coming back to. One of the best teachers in the field is the affable, Dr. Gerald Cizadlo. He teaches in Duluth, Minnesota, but makes free podcasts of all his lectures. With a recent, decent copy of Langman’s Embryology textbook and the direction of Doc C, one can glean quite a lot of useful understanding about why we work the way we do.
All tissues of the human body- brain, lungs, skin, the lining of your gut- can be traced back to what embryologists consider the three main starters- the germ layers of endoderm, mesoderm and ectoderm. By the seventh day after fertilization, the cells of a fetus are rapidly dividing and sending all sorts of chemical messages to each other, sealing the fate and destiny of many cells- the ones on the outside are destined to make up your outer skin, hair and nervous system, the cells in the middle will create the scaffolding of bones,muscle, heart and connective tissue, while the inner group will go on to make your lungs, gut and associated organs. Some of these cells will serve only as tech support and placenta not “going the distance” wth the rest of the body.
Notice in the photo that between 3 and 4 weeks the neural tube has gone from open to closed, notice also that a human embryo looks like a fish. Interesting that normal fish gestation is about 28 days…. whereas “higher” organisms gestate longer and thus fall off the embryo family tree later.
Day 24 and 25 of pregnancy are critical, as failure to close the neural tube can bring severe and downright scary results- i’ll let you google neural tube defects at your own risk. Things that can affect closure are high temperatures and vitamin deficiencies. As most women have no idea they are pregnant at this point- things can get pretty complicated. In Finland, neural tube defects were so common that people began to think Finn genetics were to blame. This persisted until a law was passed that pregnant women weren’t allowed admission to saunas.
Before modern debates arose about life, choice and rights of the unborn… Before we had ultra sound and other diagnostic techniques to check on development, a fetus wasn’t confirmed to be alive until “the quickening”. This refers to the first sensed movements by the mother in and around the 19th week.
It is at this point that neuronal circuitry is hooked up enough to jolt a kick. Laws passed about murder and abortion were based upon either quickening or formation (the period around 8 weeks after conception when designation changes from embryo to fetus or foetus if you’re into the o thing. this designation is a macroscopic one as it represents the point when the thing starts looking humanoid). In Ireland in the 1800’s If a woman was sentenced to death for a crime and she was pregnant- she was executed if quickening hadn’t arrived. If the baby was kicking, momma got a reprieve.
When a baby is born it’s proportionally all out of wack. That’s because the brain developing in utero has been siphoning off almost all the available oxygen for growth. In fact, one of the reasons why dependence of children lasts so long after birth is brain development- Whereas many species drop their kids off in egg mode and never cross paths, humans are fragile, soft and pink… requiring protection, stimulation and attention.
This of course is where all the problems may or may not begin- note Cult and paste does not endorse staples office supply.