Kelli Wise has issued an August Blog Challenge, and this post is part of the my response to the challenge.
Can I write 31 blog posts in 31 days?
We'll see. I'm getting a late start, coming in on the 5th of August, but I think that's not going to be a problem. As she said, there are no blog police enforcing this goal.
Can I keep those blog posts to less than 350 words?
No, I can't--asked and answered. What I will aim for is to stay on point, and provide valuable information, rather than just indulging my long-windedness.
You'll be the ones to let me know how well--or not--I have succeeded at that task.
The Renaissance artist Leonardo da Vinci is famous for, among other things, his sketches in which his eye for detail and his technical proficiency are immediately evident.
The veterinary medicine program at Colorado State University offers tons of information for free about comparative anatomy, physiology, and pathology in different species of animals, enough information to lose yourself in hours of reading, learning, and imagination.
In the reproductive biology e-Book, Richard Bowen has a post called "Leonardo's Error", demonstrating how even an artist as meticulous as Leonardo da Vinci can make a mistake--in his case, one that continues to this day, since he's no longer in any position to correct it.
No blame, no shame: we all make errors, and if we are fortunate, then we get an opportunity to correct those errors. The most important thing is to learn from the errors we make, and use them to do better in the future.
To understand Leonardo's error in his embryological drawings, we'll first talk a little bit about the placenta, and then go back to see how and why he got that confused.
In mammals, including humans, the placenta is an organ shared by a pregnant female and the developing fetuses.
The shared blood supply between the mother and the fetuses permits food, other nutrients, and oxygen to be delivered from the mother, and it also takes waste products away from the fetuses to be disposed of.
Source: http://upload.wikimedia.org/wikipedia/commons/f/f1/Placenta.svg accessed 6 August 2012
That's where the comparative anatomy and physiology comes it--what we just said about the placenta is true for mammals in general.
But when we look more closely at how the placenta does that job in specific mammals, then we see very real differences in how it goes about doing it.
Bowen describes the different structures in this way, with a couple of explanatory notes added in brackets:
Classification Based on Placental Shape and Contact Points
Examination of placentae from different species reveals striking differences in their shape and the area of contact between fetal and maternal tissue:
Diffuse: Almost the entire surface of the allantochorion [the membranes between the mother and fetuses] is involved in formation of the placenta. Seen in horses and pigs.
Cotyledonary: Multiple, discrete areas of attachment called cotyledons are formed by interaction of patches of allantochorion with endometrium. The fetal portions of this type of placenta are called cotyledons, the maternal contact sites (caruncles), and the cotyledon-caruncle complex a placentome. This type of placentation is observed in ruminants.
Zonary: The placenta takes the form of a complete or incomplete band of tissue surrounding the fetus. Seen in carnivores like dogs and cats, seals, bears, and elephants.
Discoid: A single placenta is formed and is discoid in shape. Seen in primates and rodents.
Source: http://www.vivo.colostate.edu/hbooks/pathphys/reprod/placenta/plac_types.jpg accessed 6 August 2012
The discoid placenta--the kind we humans have--is one discrete organ, and looks kind of like a single disk, which is where the name comes from. You can see it in the previous drawing of the mother and child--it's drawn in a uniform red color.
By contrast, a cotyledonary placenta, like sheep and other similar animals have, looks like this:
Source: http://www.ansci.wisc.edu/jjp1/ansci_repro/lab/lab12_03/images/cotelydonary_lec.jpg accessed 6 August 2012
And now, you can see Leonardo's error. He drew the human fetus like this:
Clearly, he envisioned it having a cotyledonary placenta. He confused it with the kind of placenta cows, sheep, and other similar animals have--probably because he had access to dissections of those animals, but opportunities to observe autopsies of pregnant women were relatively rare or non-existent for him.
There are, I think, 2 lessons for us here. The first is:
Consult the final authority, the human body itself.
--Stephen W. Carmichael
Even more than that, though, don't be afraid to make mistakes.
Errors happen to the best of us, even to famous artists like Leonardo da Vinci.
We can't hope to never make a mistake--they're unavoidable, simply by nature of our being human.
What we can do is to approach learning with a certain amount of humility in the face of that fact, and to hope that, when we inevitably do make errors, that we get an opportunity to correct them and to continue learning.