Crazy elegant

If you can identify the object below please ignore the fact for just a moment and tell me what the image reminds you of. It looks to me like a leaf, complete with midrib and lots of ramifying veins. The dark nodules remind me of the sort of damage produced by certain aphid infestations. In fact, this is a photo of part of a sheep placenta delivered here the other day. The mammalian placenta is a fascinating structure and one which I have discussed before. Joanna agrees that the placenta is remarkable but wonders how an image of one will be received by those who frequent this blog. Mammals are classified as either monotremes, marsupials, or placentals and differ in the way in which they house and nourish their developing embryos. Monotremes such as the platypus have retained the egg-laying habit of their avian and reptilian ancestors, marsupials develop for a brief time within the uterus and complete their growth in an external pouch, and placental embryos develop within the uterus and are nourished by a remarkable structure called the placenta, the physical and chemical link between a mother and her developing offspring. The intent of this post is not to teach anatomy and physiology but to stop to appreciate this remarkable structure. The image reveals the delicate membranes and blood supply so important in sustaining fetal life. The four nodules are cotyledons. Remember that a developing fetus is connected, via the umbilical cord, to the placenta. How the circulation of the placenta communicates and interdigitates with that of the mother is amazing. Suffice it to say that the two blood supplies do not mix (it is a popular misconception that they do) but are separated by the thinnest of protoplasmic layers. This syncytial trophoblast may be thought of as a single cell covering the entire placenta. The two blood supplies flow past one another so closely that material exchange may occur via diffusion and by active transport. Oxygen and all of the nutrients required of the developing fetus are supplied to and across the placenta and wastes such as carbon dioxide and urea are removed via the same route, but in the opposite direction. To increase the surface area for exchange, placental capillaries ramify and spread into twenty or more structures, the cotyledons, which then communicate with the maternal blood flow. Often I find myself admitting to my students that this sort of stuff is just crazy fascinating and crazy elegant. What do you think?

placenta

15 thoughts on “Crazy elegant

  1. Very interesting image and post David … I did guess biological, but because of my line of experience I thought tumours. Great to hear that it’s a healthy life producing growth 🙂

    • I love it Shimon … ‘inspirational reality.’ What great motivation to continue, without hesitation, to construct similar sorts of posts in the future. I have always been just a bit hesitant to write about such things but if even a very few appreciate them … so be it. Thanks for your supportive opinion and for taking the time to write it down. D

  2. I think I’ll go with fascinating more than elegant, though you are right that nature is indeed incredible. The colors here are beautiful and I am impressed with the level of clarity in all the vessels. I hope you share these pics with your students. A picture is worth a thousand words and really gets the point across!

  3. To answer the question, what does the image remind me of, I say it’s a little like sausage casings. I like this post, to answer Joanna’s musings. It reminds me of an essay by Mark Taylor, “The Betrayal of the Body: Live Not,” on illness and immunity. Taylor writes about the separation between mother and fetus, “the original relation between fetus and mother is not unity and harmony but discord and conflict. From the beginning, even before the beginning, self and other are divided.” He is also discussing how the mother’s immune response must be turned off for the fetal organism to develop. This statement follows Taylor’s exploration of the way we culturally discriminate, separate or “other” in terms of how we protect from illness. Fearful of death, we are fearful of sickness. To secure ourselves against disease (which is really a dis-ease), we construct mythologies of purity and immunity. Our historical use of bloodlines to create alliances and separations is an example of this fear of illness at play in our culture. Taylor’s argument focuses on the way disease is chronic, always present and endless, and that we are never unified, or whole, social units. Even from before the beginning of our lives, we are separate from each other. I don’t do the essay justice, but I like how Taylor weaves life and death together and undoes the binary that separates them, and then applies it to an ethical consideration of bias and exclusion.

    • Taylor’s dissection sounds fascinating and based, firmly, in good science. Related questions concern what it is to be an individual. Once that is resolved then one can consider the division between self and non-self. It is interesting that a botanist and a mycologist will perhaps answer the question very similarly and that both will provide answers which differ from that offered up by a zoologist. The argument made by the botanist would rest, I think, on the fact that, in a clonal, or vegetatively growing plant, the genet defines the genetic unit while the ramet defines the physical, or individual, unit. Somehow zoologists have looked past the genet when they define individuals of a pair of identical twins as individuals, for example. The botanist would point out that the twins are ramets of a single genet. Your points about self and non-self are equally fascinating. What you point out about the mother and her developing fetus is very, very cool indeed. The placenta sequesters something called phosphochline which has been called a cloaking molecule, suppressor cells of the fetus inhibit the mother’s cytotoxic T cells and, my favorite, the trophoblast (which may provide a physical barrier to immune attack) does not express a couple of the major histocompatibility genes and this hampers detection by the maternal immune system. So the fetus is, immunologically, identified as foreign and goes to great lengths (evolutionarily that is) to avoid destruction. Although my understanding of the role of MHC genes in the immunology of fertilization itself is minimal, I believe that if the mother and father are TOO similar, in terms of these genes, fertilization may not be achieved. So, in this case, some difference from self is required! Crazy. And, finally, your point about the metaphysical, philosophical, social, and even cultural issues behind these scientific ones are really, really interesting. Thanks for taking the time to forward such an interesting and thought provoking response. D

      • Oh, more food for thought! I had to read this through a couple of times, I admit, but this opens the door for me to so many interesting connections and new things to explore. Fantastic!

  4. I wouldn’t have guessed right, I had no idea what it was. With a more bluish or black background the image might trigger reminiscences of a nebula or perhaps some other astronomical (or sci-fi0 object 😉

  5. The leaf analogy is bolstered even more by the botanical term ‘cotyledons.’ Beautiful image … it really brings out the complexity of the structure. This reminds me … when are you going to do a post about mucus? Another slimy substance without which life could not exist!

    • I would so love to do a post about mucus … but am not sure it would be met with either enthusiasm or appreciation. But you are correct in that I could title the post, “Without it, like would be impossible.” D

    • Although I’ve noticed occasional similarities across kingdoms (for example, some plant seeds look like animal sperm cells), until this post I was familiar only with the botanical sense of cotyledon. Turns out the animal-related sense came first. According to the Oxford Dictionaries, the word was brought into European languages in the “mid 16th century (denoting a patch of villi on the placenta of mammals): from Latin, ‘navelwort’ (which has cup-shaped leaves), from Greek kotulēdōn ‘cup-shaped cavity’, from kotulē ‘cup’.”

      • Wow. I wouldn’t have guessed that the zoologists jumped on this one first and the term was then co-opted by the botanists! Thanks for dissecting this one for me. Joanna found it of interest as well (she’s the botanist in the family). D

  6. I saw the image on the reader first and had a feeling it would turn into a game similar to the one you played with the cream separator last year. I did spend some time examining the mystery object before reading the article and admit I would not have guessed without a lot of help. Prior to this I had only considered the placenta with respect to the discussion around harvesting stem cells from human ones. It is an amazing structure and I had never considered the extent to which it is specialized to its task (ironic that I was thinking about stem cells, the opposite of specialization). Your picture is exquisite and I am curious as to how you obtained it. Did you need extra lighting or was there ambient light? It got as high as +4 here today and the skies are now clear although we are back to zero again.

    • I think it’s great when folks ask about technique. To set this one up I took a piece of plexiglass and placed it over the open end of a 5-gallon bucket. Then I broke open the bag of tissue and tried to lay it out in something approximating a single layer. I had to fuss with it quite a bit to flatten the wrinkles and remove the air bubbles. Then I flushed the thing with a bit of water. Use a macro lens and a tripod and that was it. Post-processing involved play with mostly the highlights for it was hear that a good amount of glare could be seen. And, there you have it. Indeed … stem cells … now there’s an interesting topic (for another day) … was just talking in lecture about those last week. D

Respond to this post if you'd like.

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

w

Connecting to %s

%d bloggers like this: