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Veteran Member
Join Date: Jul 2001
Location: Seattle
Posts: 4,261
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Ok a quick recap of this thread, without all the insults:
MrDarwin started this thread to illustrate that the fetal circulatory system is perhaps suboptimally-designed, and therefore could be proof of evolution:
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MrDarwin:
The circulatory system of the human fetus is considerably different from that of the adult, or even of the newborn. Oxygen reaches the fetus from the mother by way of the umbilical cord, rather than through the lungs.
Entering at the chest would allow a direct and efficient bypass of the lungs, yet the umbilical cord of all mammals enters the body through the belly. This necessitates all kinds of odd arrangements in the fetus, including a mixing of oxygenated and deoxygenated blood, and also necessitates a drastic reorganization of the circulatory system at the moment of birth. This odd system fails to work often enough that some serious and potentially life-threatening birth defects occur regularly.
Perhaps not coincidentally, in egg-laying tetrapods (birds, reptiles) nutrients enter the fetal body from the yolk, again through the belly. Indeed, we find the same arrangement in amphibians and fish. But in fish and amphibians, however, the eggs do not have shells and develop in the water; oxygen does not enter at this point of attachment to the yolk because the developing embryos obtain their oxygen directly from the surrounding water.
The evolutionary explanation is a simple one: the position of the umbilical cord has been constrained by the position of its precursors. As we see over and over, evolution doesn't come up with new solutions from scratch, it works with what is already there, even when the resulting solution is not the best one.
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Then pz chimes in with the following:
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pz:
I'd also mention that the adult circulatory system carries peculiar vestiges of evolutionary history, as well. The primitive condition was for a single ventral major efferent vessel that branched into a pair and then branched meristically to pass through the branchial arches, where blood was oxygenated; these branches then rejoined to form a dorsal aorta that passed back into the systemic tissues. You see this same condition in modern fish, and most interestingly, in fetal mammals.
In adult mammals, our circulatory system is based on that same structure, but has been extensively modified. That primary ventral vessel pair has been reduced to the carotids, which no longer carry the full cardiac output. Instead, a short circuit has evolved to shunt most of the output directly to the dorsal aorta. That peculiar aortic arch, where the left ventricle pumps blood anteriorly which then immediately makes a hard curve posteriorly, is a consequence of that historical accident.
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Then Vanderzyden posts some stuff here:
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Vanderzyden:
There is no "drastic reorganization of the circulatory system at the moment of birth. It is not reorganized. Three "valves/ducts" close, the umbilical cord is tied off, and the baby is on its own. The original schematic of the system remains largely intact. Amazingly, at birth, the lungs begin to function (immediately!). This relaxes the pressure in the lungs, which in turn invites more blood to flow from the pulmonary arteries. Instead of crossing from the right to the left atrium (through the foramen ovale), blood now flows freely from the right atrium down to the right ventricle and into the pulmonary arteries. This reduces pressure on the foramen ovale from the right side. Since the lungs are now operational, more blood flows from the pulmonary veins into the left atrium, increasing the pressure on the foramen ovale to the point of complete closure! As the web site says, the heart therefore becomes two pumps, one that is high pressure for the arterial system and one that is low pressure for the pulmonary system! Eventually, the foramen ovale fuses to become the fossa ovalis--a permanent part of the septal wall (divider between the left and right atria).
Also, the ductus arteriosis, which connects the right ventricle with the aortic arch, normally closes within 2 days. This duct then becomes--amazingly--connective tissue which lends additional structural rigidity and cohesiveness between the aorta and the pulmonary trunk. It also prevents the one from "pinching off" the other when the upper torso is in motion. Surely this is the mark of a caring, anticipatory designer! The same thing occurs with the unbilical remnants: the umbilical vein and ductus venosus both become ligaments for the liver. In summary, the nearly simultaneous closure of the foramen ovale, the ductus arteriosis, and the ductus venosus seals off both ends of the now autonomous circulatory system.
This narrow assessment ignores the fact that the heart is located in the extreme anterior (front) of the chest cavity. The aorta has three branches immediately downstream of the exit from the heart. These branches are the brachiocephalic, the left carotid, and the subclavian. The right carotid branches downstream on the brachiocephalic. These arteries supply the brain and the arms, the access points of which are located above and to the rear of the heart. So, there must be some rotation to the posterior to serve the head (through the neck) and the arms (which are connected at the upper posterior of the torso). These parts of the body require less blood supply than the vital organs and the legs, and so do not need to "carry the full cardiac output". In fact, much blood must be supplied to the lower abdomen and the legs. Another oversight concerns the extremities of entire cardiovascular system, also known as the circulatory system. Throughout the entire body, the blood is reoxygenated and returned 180 degrees back towards the heart. Turns in the system are not defects whatsoever!
(silly and irrelevant threats to MrDarwin were left out)
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Scigirl rebuts several of Vanderzyden's claims above, and includes a passage from Moore's anatomy:
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From Moore's anatomy:
Because of abnormal folding of the embryonic heart, the position of the heart may be completely reversed so that the apex is directed to the right instead of the left - dextrocardia. Dexrocardia is associated with mirror image positioning of the great vessels...in dextrocardia with situs inversus, the incidence of accompanying cardiac defects is low and the heart usually functions normally; however, in isolated dextrocardia the congenital anomaly is complicated by severe cardiac anomalies such as transposition of the great arteries.
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Congenital malformations of the interatrial septum--usually in the form of incomplete closure of the oval foramen--are referred to as atrial septal defects (ASDs). A probe-sized patency appears in the superior part of the oval fossa in 15 to 25% of adults.
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The membranous part of the interventricular septum develops separately from the muscular part and has a complex embryological origin. Consequently, this part is the common site of ventricular septal defects (VSDs). This congenital heart anomaly ranks first on all lists of cardiac defects. Isolated VSD accounts for approximately 25% of all forms of congenital heart disease.
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With pulmonary valve stenosis, the valve cusps are fused, forming a dome with a narrow central opening. In infundibular pulmonary stenosis, the conus arteriousus is underdevelopoed. Both types of pulmonary stenosis produce a restriction of right ventricular outflow and may occur together.
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Congenital aortic stenosis refers to a group of anomalies that cdause obstruction of bloodflow from the left ventricle to the aorta. Although the stenosis usually occurs at the aortic valve, the lesion may be above or below the valve. Aortic stenosis causes extra work for the heart, resulting in left ventricular hypertrophy.
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Then she posits the following:
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Scigirl:
I wouldn't say that the human body is poorly designed, in general. It is quite amazingly "designed," and complex. However, I would say that it has the following features:
1) It is constrained by certain features of its biology. We just aren't as strong as, say, gorillas, or as fast as, say, cheetahs. These facts can be explained by our physiology.
2) These constraints, from our physiology, make sense in the light of evolution - and our evolutionary history. We would expect to have similar physiology, and similar constraints, as a chimp, than as a fish. And we do.
3) We have some evolutionary 'leftovers' which may or may not have new functions. The evolutionary relationships between these structures is confirmed through embryological studies.
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Then Lpetrich brings in some more data about the heart:
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However, the human circulatory system goes through some major reorganization as it grows, especially in the first few weeks. It starts out in a fashion suitable for a fish! The embryo has gill arches and gill pouches that are serviced by appropriately-arranged blood vessels:
Heart ->
Ventral Aorta ->
Aortic Arches that parallel the gill bars on each side of the body ->
Two Dorsal Aortas, one on each side of the body
Here are some diagrams for the chick embryo -- the human-embryo version looks remarkably similar! Or check out these comparisons (the rest of that comparative-anatomy site is also very good!).
As the embryo grows, the gill arches and the gill pouches either get reused or get resorbed (the first gill arch set becomes the jaws), and the same happens to the aortic arches. Arch set 3 becomes the internal carotid arteries, arch set 4 becomes the systemic arch, becoming effectively an aorta part, and arch set 6 becomes the pulmonary arteries. Interestingly, only one of arch set 4 does aorta duty -- the left one drops out in mammals and the right one in birds.
Also, the early embryo has vitelline arteries and veins -- these service the yolk sac! Now why would an embryo in a womb need yolk???
And the heart starts off like a fish heart -- it has two chambers and one blood path through it. As it grows, its chambers split in two and the blood path splits into two blood paths. An incomplete splitting produces the "Blue Baby" birth defect, the "tetralogy of Fallot".
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Mr. Darwin did -- connection of placental vessels directly to the heart. The pulmonary circulation could have a branch that goes to the placenta, as if it was some extra lungs. And the circulatory system could have developed in an adultlike form from the beginning.
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Then there's a bunch of debate about what the word "design" means.
Pangloss asks for some references that Vanderzyden had promised.
Then scigirl asks,
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Many facets of biology, whether they are poorly designed or not, are indicators of our evolutionary history. "Snapshots" of evolution. Evidence.
Read Lpetrich's excellent summary of the embryological development of the heart. We can yammer away about the "point" or "usefulness" of aortic arches and gill slits ad nauseum but that is not the point.
The point is - their very existence, irrespective of their function indicates and supports our theory of evolutionary history! We evolved from fish, and lo and behold, we have fishy-like hearts at one point in our embryological development.
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Then Dr Rick rebuts many of Vanderzyden's claims - here's some examples:
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rbochnermd:
These defects are real, not potential, and they are inconsistent with intelligent design.
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Elimination of omphaloceles (massive umbilical herniation), nuchal strangulation (cord wrapping around the neck), intestinal incarcerations (entrapment), and umbilical torsions (cord twisting on itself) are just some of the problems the sub-optimal design causes that could be eliminated with thoughtful consideration.
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There is no reason an intelligent design made by an omipotent and omniscient designer should have any flaws; a good design would not have any problems to discuss.
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Criticism of a sub-optimal design is not dependent on offering a superior design.
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Substitutes sought after to compenste for the sub-optimal design of the human circulatory system in the first place.
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An intelligent design would do exactly that: the oxygen requirements of the liver are much less critical than those of the brain and heart.
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It wouldn't be difficult at all if it was designed intelligently. The organs of the chest are no more compressed than the abdominal viscera, and they are better protected. An intelligent design would take advantage of the latter and place something as critical as the fetal "lifeline" in a position where the thoracic skeleton could protect against injury and herniation.
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Bad design; it can reopen later in life and create a hernia requiring surgery. The ligamentous remanants can also act as fulcrum that can twist the intestines into a fatal knot (volvulus)
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A nice summary of conversion from a undesigned fetal circulation to a undesigned anterograde circulation. The description does not support intelligent design.
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Zetek brings up this point:
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Zetek:
And this explains the circuitous route of the recurrent laryngeal nerve. In fish, the nerve has a direct route under the fourth arch. In mammals however, the modification of the arch setup results in the nerve being "dragged" into the mediastinum with the descent of the heart.
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Then MrDarwin restates his original question:
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MrDarwin:
Apparently I wasn’t specific enough. It’s really very simple: if the umbilical cord entered at the chest, i.e., closer to the heart, the umbilical artery could attach to the trunk of the pulmonary arteries, which would normally be taking deoxygenated blood to the lungs. With this attachment, it would take them to the placenta instead to pick up oxygen (and other nutrients). Of course a small amount of blood would still flow to the lungs, as it does in the current system. Meanwhile, the blood returning through the umbilical vein could attach to any one of the pulmonary veins (another odd design feature—why are there 4 pulmonary veins, one from each lung, each with its own entrance to the left atrium?)--or even directly to the left atrium itself--which would normally be bringing freshly oxygenated blood from the lungs. The entire circuit, with the exception of the umbilical vessels, is exactly the same as in the newborn and adult. When blood flow to and from the umbilical cord is shut off, the attachments close (as they do in the current system, except there are fewer of them). The three major advantages of this are that there is no hole in the heart that has to close (one of the major sources of birth defects), no ductus arteriosus to be patent, and no mixing of oxygenated and deoxygenated blood (one of the reason why these defects are so serious in newborns).
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Dr Rick confirms his speculation:
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rbochnermd:
MrDarwin's intelligently designed fetal blood flow would be an improvement over the evolutionary one that humans are stuck with, and for precisely the reasons he gave as it would obviate the need for either a ductus arteriosus or foramen ovale. MrDarwin's concept would work even if the the umbilical artery attached to the thoracic systemic vasculature instead of the pulmonary arteries as the lungs receive blood not only via the pulmonary arteries but also the systemic bronchial arteries. In other words, there are several potential design possibilities that would be an improvement over the unintelligent one we now have.
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Now we are on page 3.
Vanderzyden asks some more questions (and interestingly enough, continues to ignore a major portion of the scientific data presented to him, such as aortic arches.
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Vanderzyden:
Major problem right from the start, as I explained in my first response. How are you going to negotiate the breastbone, ribs, pericardium, lungs and/or diaphragm in order to make this attachment robust and yet easily disconnected? How will you redesign these other organs/components to accomodate this new plumbing?
Also, with this configuration, how will you accomplish the management of fluid pressure, before and after the baby is born? In particular, how will you prevent the higher pressure of the umbilical flow from inflating the lungs? Since you have placed the junction downstream of the heart, how will you redesign the heart so that it (1) handles the significantly different (reverse) pressure load and (2) adjusts properly when the baby begins to breathe for himself?
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Lpetrich answers some of his questions here:
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lpetrich:
I don't see how Vanderzyden's "problems" are big disasters, because the existing arteries and veins already go through the pericardium, and umbilical blood vessels can easily attach to the pulmonary vessels once they are past the pericardium.
As to getting past the ribcage, the navel could be at the lower end of the breastbone, meaning that the umbilical blood vessels could follow the breastbone to it.
And this does not address such questions as:
Why the heart starts out with only a single blood path instead of two; it has to internally split into two sub-hearts.
Why the initial embryonic circulation is the fishlike arrangement of
heart -> ventral aorta -> aortic arches -> two dorsal aortas
and why it has to be extensively rearranged
Why jaws are made from the frontmost gill bars
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Dr Rick once again refutes Vanderzyden's claims, here:
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rbochnermd:
(v asked "Major problem right from the start, as I explained in my first response. How are you going to negotiate the breastbone, ribs, pericardium, lungs and/or diaphragm in order to make this attachment robust and yet easily disconnected?"
This isn't even a minor issue; we doctors routinely and easily access the thoracic vasculature with trocars and catheters above and below the clavicles. The thorax is not solid, there are lots of avenues to access the vasculature, the heart and the lungs through it, including between the ribs and above the sternum.
(v asked "How will you redesign these other organs/components to accomodate this new plumbing?")
We doctors don't have to redesign the thorax every time we insert a central line or catheter into the heart, lungs, subclavian vessels, or aorta; MrDarwin's intelligent design would not require any such reconfiguration, either.
(v asked, "Also, with this configuration, how will you accomplish the management of fluid pressure, before and after the baby is born? In particular, how will you prevent the higher pressure of the umbilical flow from inflating the lungs?")
Infant lungs are inflated by negative inspiratory pressure just as yours are, not by blood flow.
(Since you have placed the junction downstream of the heart, how will you redesign the heart so that it (1) handles the significantly different (reverse) pressure load and (2) adjusts properly when the baby begins to breathe for himself?)
The pressures would not be reversed.The direction of blood flow is maintained by the heart valves, not the placement of the umbilical blood vessels.
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What was Vanderzyden's amazing rebuttal to a physician discussing basic physiology about the heart?
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Vanderzyden:
Your reply doesn't really address what I said, and it is merely a collection of claims. Care to explain in detail, as I have done?
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Then Mr Darwin again asks Vanderzyden some questions:
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MrDarwin:
Can you tell me why blood coming from the placenta is under "higher pressure"? Higher than what? Precisely where and how is this pressure being generated? Of course, there's that tiny detail Rick raised about just why the pressure of blood would inflate the lungs; you might want to go back and review the website I linked to in the OP:
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Could you please point out in precisely which "many places" this mixing would occur?
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Then we get this question:
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NialScorva:
For a real question, if it can be answered in the midsts of Vander's floundering:
Going back to the original comparison of routing in the fetus to that of a fish's two-chamber mixed oxygenated/de-oxygenated blood, what are the evolutionary routes torwards mammalian hearts?
IOW, how does the development of amphibian and reptile ubilici (sp?) into a mature circulatory system progress?
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Then Dr Rick attempts once again to elaborate on his answers.
Vanderzyden, apparently tired of talking about fetal hearts, has chosen to change his tactic to proving doctors are arrogant, and quotes random bits of Dr. Rick's posts to do so.
Finally he attempts to answer a question:
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Vanderzyden:
Permit me to answer in your terse manner: False. The mother's blood pressure is indeed a factor in umbilical inflow pressure. The mother's and infant's blood pressure are somewhat correlated, as evidence by conditions such as preeclampsia. Anyway, it really doesn't matter. Most of my concerns are still valid, with or without additional umbilical pressure.
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Dr Rick replies,
Quote:
rbochnermd:
You are wrong, and your answers and concerns are invalid. Circulatory fetal pressures are not driven by either placement of the umbilical vessels or the placenta. You asked me to educate you, so read the following carefully: placing the umbilical vessels in the thorax instead of the abdomen would have no affect on fetal circulatory pressures. There would be no change in the pressures, which are driven by a pump (the heart) whose effectiveness would not be compromised by moving the umbilical vessels into the thorax.
Thoracic umbilical vessels could access the thoracic vasculature by several different routes.
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Vanderzyden, like I said before, has abandoned once again the science, and characterizes Dr Rick's rebuttals in the following manner:
Quote:
Mere claims, Rick. Claims, not explanations. You do not explain.
Here is a characterization of our exchange:
V: Explain, explain, explain....
R: Wrong. That's it. Goodbye.
V: Explain, explain...
R: You don't know what you're talking about.
V: Tell me specifically what's wrong.
R: How dare you question me? I am a surgeon. I cannot possibly be wrong on this.
V: Explain more. Indicate that doctors are not divine.
R: No, you don't understand, you are "unqualified". You are "beneath" me.
V: Explain more...
R: You are "deluded".
I thought we could have a discussion. Instead, I'm told that I have no business questioning a medical authority.
So, what's the use of proceeding?
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Dr Rick replies:
Quote:
I've explained in very simple terms, despite your assertions to the contrary, why it's not hard to access the thoracic viscera and vasculature, why there would be no problems with pressure changes and reversed flows, why the fetal circulatory system does not appear to be intelligently designed, and why your objections to potential improvements if there was intelligent design to the system are groundless. I've also explained my background because you asked me about it and wrongly asserted that I don't know this subject, an ironic accusation, to say the least.
I can not more simply explain to you why you are wrong when I have employed such simple and straight-forward explanations already. There's no more simple explanation needed than that the thoracic innards are easy to get to (you claimed they are not) because the thorax is not solid, and the ribs and clavicles are easy to get around. I provided simple examples of how it is done every day. How can this be beyond your comprehension?
You have been repeatedly advised that the pressures in the fetal circulation would not be altered by moving the umbilical blood vessels because the pump that drives the pressure would not be affected by such a shift (you claimed it would be).
Here is a characterization of our exchange:
V: The proposed improvements to the fetal circulation wouldn't work for a bunch of reasons that make no sense.
R: They would work; your objections are not valid for the following reasons....
V: You're not a surgeon, you're not qualified to argue with me, and you're going to hell.
R: I'm a very specialized surgeon, in fact, and I know exactly what I am talking about, but you do not.
V: I'm shocked! What an unfair thing to do! How dare you question my qualifications?! You're going to hell!
R: You don't know what you're talking about.
V: Tell me specifically what's wrong.
R: One more time, here's why the thorax is easy to access, the circulatory pressures wouldn't be altered, and the design would work...
V: Explain more. Indicate that doctors are not divine.
R: No, you don't understand, you keep making spurious claims, and I never claimed to be divine: you're the one that first bought an ad hominem challenge. There is no reason that the proposed mechanism wouldn't work and prevent some of the problems that accompany the evolutionarily derived fetal circulatory system we now have.
V: Explain more...oh, don't bother: you're going to hell.
R: You are "deluded".
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Then Vanderzyden makes two more posts:
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Rufus: You're right I should not get hung up on this topic. However, I won't be contributing to that thread any time soon, since I have several other requests pending.
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and, my personal favorite, this last one here:
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DD,
You will note that I avoid engaging several people in various forums. In fact, there are many complaints and apologies that result from my refusal to waste time in pettiness.
You and I have had similar discussions, and you know that my concern is not damage to my vanity. Rather, I encourage efficiency and sensibility. My aim is to discover the truth about ultimate things. You should know me well enough now that I have no ulterior "ambitions" or "agenda".
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Hmm, insults were thrown around by both sides obviously. However, did we leave any of Vanderzyden's questions unanswered? No. He didn't like the answers, but we did answer them.
Did he answer our questions? Very rarely did he even attempt. The data is clear - Vanderzyden is not interested in having an enlightened science conversation. Instead, he is a 'question dodger,' a changer-of-the-subject, and when he can't put forward or defend a good science argument, he attacks the members of infidels.
My suggestion - put this guy on our ignore list and do something more efficient with our time.
scigirl
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10-23-2002, 11:28 AM
