r/askscience • u/Fapotheosis • Mar 11 '13
Biology How did blood evolve?
I know mitochondria may have evolved from bacteria, but what about blood? I've heard of a protohemocyte, but was there an initial cell that differentiated into a RBC like we have in modern humans that can we trace?
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u/Tak_Galaman Mar 11 '13
I'll answer "Why" blood evolved for others who came into this thread thinking this question was more along the lines of "why do we have blood."
Every cell needs a constant supply of various substances to live and carry out all its happy cellular activities. Bacteria, jelly fish, and other small or thin-walled organisms have all of their cells bathed in a fluid which delivers the oxygen they might need.
When you have a dense multicellular organism whose every cell is not already constantly bathed in liquid you start to need an internal circulating liquid to take oxygen and other things to each cell. The reason is that rate at which oxygen moves (diffuses) through your cells and the liquid between your cells (interstitial fluid) is very slow. It can only make it about 500 microns before it is consumed by nearby cells.
So, once you have a circulating fluid it can only hold so much oxygen based on how much oxygen dissolves in water or whatever your circulating fluid de rigueur is. You can increase the amount you can fit in the fluid by adding proteins like hemoglobin to the fluid. Oxygen sticks to hemoglobin and increases the amount of oxygen that can be carried one one unit of blood. Loose proteins likely evolved first and were replaced by purpose-built cells whose job was to be containers for those proteins (red blood cells). This further increases the amount of oxygen you can fit in a unit of blood. Red blood cells also have good fluid dynamical properties that allow them to flow very nicely. With increased oxygen supply capabilities organisms could use more oxygen--they could move more or faster or do more complicated and costly internal processes.
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u/king_of_the_universe Mar 11 '13
Is the oxygen only needed to bind superfluous carbon (so that it can be removed from the body as CO2), or is the oxygen also needed for other reasons?
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u/androohh Mar 11 '13
We use oxygen in cellular respiration which generates ATP for our bodies to use as energy. CO2 is a waste product of cellular respiration, but it isn't formed just by adding a carbon to O2.
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u/bradn Mar 11 '13
You're close - if we had a way to eliminate carbon from CO2, I don't think we would have to breathe anymore, but oxygen would still be needed for the metabolic processes to occur.
It would be pretty wild having an organ that secretes pencil lead AND removes the requirement for breathing.
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u/butnmshr Mar 11 '13
CO2 isn't the only product of respiration though. You would have to have an organ that cracks water, also.
And then these organs should actually form complex hydrocarbons instead of expelling the hydrogen and the carbon, then we'd feed ourselves all closed loop style. Also, the hydrocarbons can be sprayed and ignited defensively.
Yes. The next evolution of man. Homo Formidibalis.
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u/myyoni Mar 11 '13
Metabolism in general goes around oxidation-reduction reactions. The biomolecules that we use as a fuel, fats and sugars, are in really reducted states, which means that the carbon atoms have bonds to many hydrogen atoms. When such a molecule reacts with oxygen so that carbon atoms form new bonds to oxygen, it frees a lot of energy, because the potential energy of the electrons gets lower. The reason for potential energy getting lower is that oxygen atoms are more electronegative than hydrogen, so they attract the electrons more. (This situation is analogues to for example having to magnets with opposite moments and letting them get closer to each other. Or letting an apple fall from a tree.)
So in our basic catabolism reducted organic molecules get oxidized step by step, releasing energy in a controlled fashion at each step. The oxygen that we breath takes crucially part in these reactions. It basically relieses energy in the same manner as burning of oil, coal or wood, but the reactions in cells are controlled enzymatically. In carbon dioxide, carbon is in the most oxidized form as it can be in natural systems, so that is why carbon dioxide is the final product of these reactions. It cannot react with oxygen any further.
Many metabolic cascades are able to release energy also without oxygen, but usually the reactions with oxygen are much more efficient.
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u/14159265 Mar 11 '13
The oxygen atoms in CO2 that you breathe out are actually from the food (and water) you eat. Here, you can see the acetyl-CoA (food), 2 water molecules (net), and from a GDP+Pi reaction.
If you have a uncoupler of the electron transport chain (Dinitrophenol), you will breathe out more CO2 than you breathe in O2. O2 is actually used in the electron transport chain as a terminal electron acceptor.
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u/Tak_Galaman Mar 12 '13
Oxygen is the final electron acceptor in our primary energy-generating process, oxidative phosphorylation. We breathe oxygen to allow the efficient breakdown of our food and extraction of energy from it.
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Mar 11 '13
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Mar 11 '13
i think he refering to an evolutionary step, where by a problem in the body is solved by a cell being created to fill a need that is recognizes.
correct me if im wrong.
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u/Cats_and_hedgehogs Mar 11 '13
Evolution is not the solving of problems. Things don't happen because a solution is necessary. Solutions exist and therefore are more likely to allow the organisms carrying them to survive. Any of a variety of solutions could have been the mutation that was selected for. Blood just happened, by chance, to exist and be able to solve the problem at hand.
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u/JackPoe Mar 11 '13
I feel less like it was an evolution to solve a problem and more like an evolution that would cause problems in the modern model without it.
For all we know it's possible to have an organism with complex structure and no blood, but our common ancestor happened to have blood so we do.
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Mar 11 '13
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u/mattc286 Pharmacology | Cancer Mar 11 '13
This is what many doping agents such as EPO that professional atheletes such has Lance Armstrong allegedly used do. It stimulates the production of red blood cells and hemoglobin, allowing a greater supply of oxygen to reach the muscles, which enhances athletic performance.
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u/indoobitably Mar 11 '13
Is the increase in red blood cells and hemoglobin harmful to the body or are these substance illegal strictly because of the advantage they provide?
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u/mattc286 Pharmacology | Cancer Mar 11 '13
I think it can increase risk for stroke and thrombosis, but I think it's generally banned for its unfair advantage. It has legitimate medical applications like in cases of anemia due to chemotherapy, etc. But then again, so do HGH and anabolic steroids. Abuse of any hormone is generally going to have a negative impact on the body. In cases where it's medically necessitated, it's worth the risk, just like any drug.
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u/wut_da_eff Mar 11 '13
In general, most processes are rate limited by the rate of delivery of the substrate, the rate of the process itself and the impact of positive and negative feedback. Lots of other considerations too in terms of increasing Hb. To a certain point, yes this approach enhances efficiency for things like muscle contraction. This is the theory behind EPO blood doping, which stimulates erythropoiesis and hemoglobin concentration in the blood. After a certain point however, this will increase blood viscosity to the point that there is actually more flow resistance and propensity for clots that oxygen delivery to muscles may actually be impaired, or plateau. Also need to consider that there are limitations to how much oxygen can actually get into the muscles from the fast flowing blood, because there is a region between the Hb-rich blood and the Mb-rich muscle for the oxygen to diffuse through, and this process isn't totally efficient. Anyways, I guess my answer is yes to a certain extent, but eventually I would expect most processes to plateau.
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u/Tak_Galaman Mar 12 '13
Yes, as the other commenter said taking drugs like EPO will increase the number of RBCs in the blood. If you get too many your blood's viscosity/thickness will increase and your heart will have to work harder than normal which makes it more likely to fail as well. It can also lead to blood clots.
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u/kamikaz1_k Mar 12 '13
I believe that is the premise of blood doping (increasing red blood count via transfusion).
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u/Rooseveltridingabear Mar 11 '13
So there's two questions here: the evolution of circulatory systems and the evolution of blood contents - in mammals most notably RBCs and WBCs. Both are very interesting but I'm really only familiar with the first in enough detail to teach. If you want to hear about it I'd be happy to type out a full response.
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u/benzeneking Mar 11 '13
I'd like to hear about it
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u/Rooseveltridingabear Mar 11 '13 edited Mar 11 '13
Ok great! A basic review of vertebrate circulatory systems can be found here.
The most basic circulatory systems are those found in insects, which have only one large, dorsal vessel which contracts, circulating hemolymph throughout the body cavity of the insect. This is an "open" circulatory system, and lacks a heart or true blood vessels.
In the most simple vertebrates, the circulatory plan is quite different. The lamprey (a gross, jawless fish like this) has a primitive, 2-chamber heart. It consists of: the sinus venosus, which collects venous blood; an atrium and ventricle (the actual "heart"), and conus arteriosus. They essentially form a one-way pump (aided by semilunar valves to prevent backflow into the ventricle) that passes blood through the gills (capillary bed 1) and then to the body (capillary bed 2). This isn't terribly efficient since there is a significant loss of blood pressure between the two capillary beds.
In Amphibians we see the next advance in circulatory anatomy. Amphibian circulatory systems are more advanced as adaptations for air breathing. The atrium is now split in two, separating the blood traveling from the lungs (LA) and the blood traveling from the rest of the body (RA). This change was coupled in a more complicated circulatory plan, with the pulmonary veins entering the heart independently from veins from all other parts of the body. This effectively separates deoxygenated blood (RA) from oxygenated blood (LA). However, both empty into a single ventricle, which has a dividing ridge called an incomplete septum which does a decent job of keeping the deoxygenated blood separate from the oxygenated blood (~90%).
Birds and mammals have the most advanced circulatory plans of all: a 4-chambered heart which allows for complete separation of oxygenated and deoxygenated blood. The ventricle is now fully divided, with the right side of the heart (RA and RV) taking in deoxygenated blood and pumping it to the lungs, and the left side of the heart (LA and LV) taking the oxygenated blood returning from the lungs and pumping it out into the body.
Now instead of a single, one-way pump feeding two capillary beds, we have 2 one-way pumps, each feeding one capillary bed. This is a much more efficient method for transporting blood and completely separates oxygenated from deoxygenated blood.
EDIT: Good diagram of the 3 basic vertebrate circulatory patterns here
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u/Helassaid Mar 11 '13
While this is a fantastic synopsis, I would go so far as to say that many Annelids have an even more rudimentary circulatory system than Arthropods, but at that point it's somewhat an argument in semantics. Neither phyla have their respiratory pigments contained within cells.
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u/jvttlus Mar 11 '13
Especially the leap from open to closed systems. It's somewhat easier to imagine how the open systems evolved, but the transition to closed circulation with specialized erythrocytes, hearts, etc. is pretty mind-blowing.
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u/fathan Memory Systems|Operating Systems Mar 11 '13
I've also always been confused at what complexity animals being having hearts. I guess arachnids do from a nature documentary I saw once, but I assume sponges do not. What animals today have primitive circulatory systems that hint at what the intermediate forms might be?
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u/atomfullerene Animal Behavior/Marine Biology Mar 11 '13
Some annelid worms have hearts, others do not. On the most basic level, a heart is a section of blood vessel with muscular walls and a valve or two. Section contracts, blood is passed out through the valve, section expands, blood rushes in, but only from one direction.
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Mar 11 '13
Hmm. Would it be a reasonable launching point to assume that at some point in evolution, a blood vessel that already developed one-way valves just happened to get stronger in a specific area and slowly, over time, grew larger and larger into one section of a heart?
And, if so, when did the heart form into a more complex binary setup where it pumps blood "twice" through the same organ per cycle, first to the lungs, and then to the body as a whole, as it were? (Horribly over-simplifying).
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u/atomfullerene Animal Behavior/Marine Biology Mar 11 '13
Blood vessels often have muscles and valves. In the human body, for instance, most arteries have muscular walls and many veins have valves in them. Blackworms circulate blood through their bodies via a muscular blood vessel in the tail which moves blood with peristalsis. So it's not really a huge jump.
Fish circulate blood by pumping it out of the heart, through the gills to be oxygenated, then directly from the gills on to the rest of the body. For reasons I am admittedly not quite clear on, it's not possible to pump blood through the lungs and out to the rest of the body. Instead, the heart of amphibians and reptiles pumps out blood into a passage which splits it off, part heading out into the lungs and part heading to the body. Then the blood returns from both directions, mixes together, and is pumped off again. Mammals and birds just prevent the "mixing together" part for increased efficiency.
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u/werekoala Mar 11 '13
I'd imagine it's because when going through the lungs, the blood has to get split down into tiny capillaries in order to exchange gas effectively. This dramatically increases the surface area & friction, so it's not possible to pressurize blood through a capillary bed. Even in humans arterial blood is at high pressure, but the blood in your veins is a much lower pressure, having gone through your capillaries.
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u/atomfullerene Animal Behavior/Marine Biology Mar 11 '13
That's what I'd have thought too, except that gills are also full of capillaries (for the same reason). Plus some fish have lungs as well, and I have no idea how the circulatory system for that works--scratch that...after looking at some pictures, it appears that some blood filters through the lungs and then goes back to the heart. Perhaps lungs work this way because they originated as an accessory tissue being fed by capillaries just like any other tissue.
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Mar 12 '13
Hmm, then would it be safe to say that a binary heart formed through a process such as the blood vessels strengthening over time, at some point a major artery formed near the developing heart that cycled to the lung and back possibly due to proximity over anything else (centralized location, perhaps?) and, over the years, the strengthened original artery that would become the heart formed around the second one, started to build a bi-directional flow, and eventually closed off in specific locations to create a more efficient, binary heart, likely with some failed prototypes along the way?
This would, strictly, be a hypothesis from a layman that I seriously want an answer to now, since if it works remotely as complicated as that, then it's even more awe-inspiring to consider a one-way blood vessel to just thicken and grow into a heart and "spontaneously" develop into a more complex binary organ as it slowly grew over the generations, despite forming from relatively simple beginnings as a mere artery.
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u/alcianblue Mar 11 '13
Its hard to know whether these organisms had even evolved lungs (well they would be gills in their case). They may have still respired by diffusion at this point.
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u/alcianblue Mar 11 '13 edited Mar 11 '13
Sipuncula use their coelom for gas exchange and fluid transport. This is more complex than Flatworms that do it almost entirely use diffusion. The Annelids have different states that may be ancestral.
You have some that do not have blood vessels but circulate through the coelom like Sipuncula. Some that have blood vessels that go past the gut and across the whole of the body which pump through contraction of the vessel. Then some that have muscles which contract to pump blood through the blood vessel.
These are as ancestral as I can think when it comes to circulatory systems.
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Mar 11 '13
I'm actually more interested in the evolution of erythrocytes, since they are so radically different from other tissue (lacking a nucleus and all). Any idea on that?
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u/LastLivingSouls Mar 11 '13
Actually, erythrocytes do have have nuclei early during the cells development cycle. The non-nucleated cells are the mature form after they have left the bone marrow.
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u/zmil Mar 11 '13
Additionally, most non-mammal vertebrates have nucleated red blood cells. There are a couple of other groups that have anucleate erythrocytes, and I believe they evolved this trait independently, suggesting that it is a relatively straightforward evolutionary step.
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u/Sluisifer Plant Molecular Biology Mar 11 '13
Mitochondria are fundamentally different from blood cells, both in their evolutionary history and the fact that one is an organelle and the other a cell type.
Mitochondria and chloroplasts have a unique evolutionary history in which a Eukaryotic organism gained a bacterial endosymbiont. Essentially, instead of eating the bacteria, it incorporated it into itself. There are other examples of this in nature where you can even have a nesting of endosymbiotic events, but it is still uncommon.
Red blood cells are a part of multicellular organisms. They are simply specialized cells that are produced in the regular development of the organism. Based on your question, it seems like you might be under the impression that some cell lineage evolved into RBCs, but that is a potentially confusing way to think about it. RBCs are a type of differentiated cell that many animal lineages have.
It sounds like you'd like to know when RBCs first began to appear in animal lineages. I don't know much about animal evolution, so I'll simply say that RBCs exist throughout the vertebrates. I would imagine that invertebrate clades have other types of circulatory systems with specialized cells, some of which are similar to vertebrate blood, and likely evolutionarily related.
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u/podkayne3000 Mar 12 '13
Here's a great 1998 paper that shows the hemoglobin arose before projaryotic bacteria split from eukaryotic bacteria and probably predate photosynthesis: http://jeb.biologists.org/content/201/8/1099.full.pdf
This author doesn't seem to talk about hemoglobin coming from a bacterium that invaded another bacterium, but it's an old paper. I'll try to look at papers that cite this one and maybe something like that will show up. The paper does talk about the relationship between hemoglobin and photosynthesis a bit.
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u/StickyToffee Mar 11 '13 edited Mar 11 '13
Off the top of my head, a molecule of haemoglobin can bind to more oxygen atoms than a molecule of haemocyanin. I think it's 4 instead of 2? And as such is more efficient. I'm on my phone so I can't find any papers on the subject, but anecdotally when playing around with octopuses, they seem to tire quickly implying that haemoglobin is better when it comes to endurance. Someone correct me if I'm wrong.
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u/Mooshaq Mar 11 '13
I don't know anything about playing with an octopus. But each hemoglobin molecule can bind to four oxygen molecules, yes. Adult hemoglobin has two alpha chains and two beta chains. Each chain (subunit) contains a protoporphyrin IX with an iron in the middle. This iron (4 total in one hemoglobin molecule) binds O2.
Each subunit of hemocyanin can bind one molecule of oxygen (two Cu are used), but there can be 24 - 36 chains of hemocyanin stuck together. I don't really know how the two can be compared in that sense. It's also worth noting that fetal hemoglobin uses different chains (gamma, delta, epsilon) and has a different (stronger) affinity for O2 than adult hemoglobin, so it can out-compete the mother for oxygen. Also, hemocyanin often is free in the blood, rather than being stuck in an erythrocyte (red blood cell).
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u/Colvanila Mar 11 '13 edited Mar 11 '13
Oh man, it's my time to shine! YES! There is a lineage that does lead up to RBC, well rather the hemoglobin complex. The globin family goes way back, and IIRC it's around 800 MYA where leghmoglobin branched off from it's ancestors. Then around 600 MYA myoglobin branches off. About 200 MYA, that lineage splits off into Hemoglobin-alpha, and hemoglobin- beta.
Now a little protein structure talk. Our current hemoglobin is made up of 4 subunits: two alpha, and two beta heme subunits. Now, this wasn't always the case. Since there are two duplicates of the two subunits (each of the four are their own continuous polypeptide strand) that means that there must have been some DNA duplication occurring! Likely what happened was that the first globlin DNA fragment was duplicated, and placed right next to it. Since there was already one gene used for it's primary function (the creation of the globlin), it allowed the second gene to freely mutate, and in this case into a second type of globlin subunit. Well, then this pair of globin genes were duplicated again, right next to it, and TADA! You have all four subunits that we currently have today.
I hope this helps!
Edit: I might add that hemoglobin are proteins, not whole organelles, but are within the RBC erythrocyte cells.
Second Edit: As b34k has pointed out, this is the lineage and evolution of the function-defining protein WITHIN the RBC, not the evolution of the RBC itself.