The Poll question:
Are Red blood Cells alive? Yes? No? Maybe? Can you give your reasoning or belief?

Happy thinking!

viruses are DNA or RNA in a protein capsule that can enter a specific host cell and uses the cell's machinery to selfreplicate. Their exactly like a computer virus - a piece of selfreplicating material.

But it all depends on what definition you want to use.

Some keep it loose - any "ability to replicate". Some narrow the definition a bit - "ability to self-replicate"; some add "reacts or adapts to environment"; some add more "can maintain an internal environment" (homeostasis), etc.

look up life in wikipedia and they have 7 or 8 guidelines that biologists use to define life. By those guidelines a virus is not alive.

One interesting definition is living things "extract energy from it's environment." (which goes hand-in-hand with the energy needed to maintain homeostatis). Viruses don't do this.

So, if you define a WBC cell as alive, then so is a RBC. However, WBC cell cannot create more WBCs only the stem cells in the marrow can do that, this is also true of RBCs. Usually, a cell the undergoes terminal differentiation loses the ability to reproduce, but I may be behind on my literature on this one. the field of stem cell biology is crazy right now and thank god for that!

When you compare life, it's not a fair comparison to talk about RBCs and viruses. An RBC is a component of a living organism. Is a mitochondria alive? I would not hazard a guess now, but it likely was at some point. Now a virus, that's one for the philosophers but it seems pretty clear that the definition of life is on a sliding scale.

Leslie

Yes, RBCs in mammalian cells are anucleated. But they most definitely have nuclei in birds and reptiles, yet do not replicate and perform the same function.

To your point "Normal cells- eat, grow, adapt, replicate"
Well, no. actually they do not. They definitely eat and grow and some can adapt but not all- many terminally differentiated cells just die in a new envrionment. Many cannot replicate- as I said above. Are those dead? No they are part of an organism.

I think we maybe be thinking of different meanings of 'adapt.' I'm thinking adapt as used in the science of pathology - typically adaptation to cellular injury caused by noxious stimuli. Anucleated (i.e. dead) cells don't adapt.

Edit: Also differentiated cells can replicate - T-cell and B-cell proliferation to cytokines are one example.

Note that differentiated cells aren't permanently that way - they still have the original genome - it's just turned off. With the right nuclear signals you can turn them back on. It all depends on the stimuli. Also note there is a thing called dedifferentiation (not in humans though...)

So I still stand by eat, grow, adapt, replicate - even for differentiated cells. it all depends on the stimuli. Any cell can die in a noxious enough environment. Some cells are more sensitive. But they are alive.

Mature human (I had though human was implied, but i'll be explicit) RBCs don't adapt at all to noxious stimuli. They just get destroyed. In fact they don't eat, or grow, or adapt, or replicate.

It's cause they're dead.

I looked at the requirements you listed for a cell to be considered "alive". If all of these are required, then we might as well say thay we are all brain dead after about 25 years of age, which you may think about me at this moment. Brain cells (neurons) do not have many of the qualities that are listed here - such as homeostasis (since they do not exist independently), growth, adaptation (very limited, especially after age 25), or reproduction. I would suspect there are a variety of cells (other than RBCs) within living animals that also lack many of these qualitiies. These requirements would seem more appropriate for independent living organisms.

Neurons do go thru all the guidelines of life - they grow and adapt - neural plasticity is an example nicely covers all those. the only thing it doesn't do on it's own is replicate -- but with the right signals it can be pushed from G0 state to G1 - but that is considered a pathology of neurons. Dead cells dont respond to signals. All the rules of life are there for every cell- it's just the proper signals keep everything in check.

quote:

---

RBCs don't 'die'

---

Yes I was thinking of evolutionary adaption and you were thinking environmental, but they do cross. And you do realize that this is like debating the length of a string, right? LOL.

You are correct on that blood cells do adapt, in a sense, in those cases. B & T Cell Proliferation is a very specialized kind of terminal differentiation and also requires marrow and stem-like progenitor cells. The cytokines trip the process to create specialized pools of differentiated B/T cells. Once those specialized cells are created they cannot go back to being non-specialized. There are also cells in the brain and gut that are actually a better example for your argument because they do not require a progenitor pool and probably other places that I do not know about. 8-)

And as you note dedifferentiation is not in humans and only very recently found in a planaria-like thing (I cannot recall what it was..). Also not all differentiated cells contain the full genome, many do not. There were a number of chimera studies in the early 90s that showed that during development in certain tissues genes were not just turned off during embryonic development but genetic material was lost. Those were in mice, mommies frown on freezing and slicing up little bobby.

However, I think my argument of blood cells as a part of a living organism and therefore the apples and apple orchards argument is the most reasonable.

Is a mitchondria alive? A nucleus? A panceas? Testes? (still reading?) All of those are living tissues. Blood is living tissue and RBCs are a component of living tissue. I don't think that the argument stands up because you are talking about something that is an integral part of a living tissue. It is complex and cannot be sustained outside of the body. Can you keep a glass full of blood alive or active or whatever, without some preservative outside of the body? No, you need something to keep it liquid and slow down the reactions. You cannot do that with compacted RBCs either, they turn into a mass of useless goo, even if you clean away everything else. It's because there are complex biochemical reactions (ATP is definitely--> ADP in a mature RBC), they have lysosomes and lytic reactions and are chowing through glucose in a manner that we call life for whatever is going on inside them. So if you want to keep them to play with outside the body you have to slow them down. They are definitely jumping around - at least biochemically.

Mature RBCs are sufficiently complex and integral part of a tissue to be considered alive.

First I don't see the connection between Differentiation and the criteria for life. Second, just calling a tissue 'living' doesn't make it so. Is it the serum - the platelets, the proteins, the lipids, the sugars, etc - that's 'living'? Or did you mean the cells in blood tissue are 'living'? Just makin' a point...

But moving on...I'm getting the idea that you're trying to say using terms like 'alive' or 'dead' is moot since it's all biochemistry anyway.

But then why even call *any* cell alive at all? - just call the entire human body dead or inanimate since it's all molecular interactions anyway. We can say it's all bio-machinery - it's all inanimate stuff reacting to it's environment on a massive scale.

...Or is there a specific criteria beyond the sum interaction of biomoleclues that is defined as 'living'? I think you can agree there is. Then what is that criteria for living cells? - and do RBCs have it?

I'd wager they don't.

To me, homeostasis is the topmost necessary (but not sufficient) criteria for life - and RBCs don't even have that.

Mitochondria and gametes are definitely on the fence since they fit most of the criteria for life.

On those two I could swing either way and it would probably require refining the criteria to come to a definite conclusion.

Tree branches and bark are not alive. Plants only grow from certain regions within the plant (Meristems) the epidermal regions of humans are the same, our skin does not develop on the surface cells are produced, cease to function, and shed.

Here is my take.

A. Red blood cells are cells whether they have a nucleas or not.

B. There is a big difference between a functional (live) RBC and a nonfunctional (dead) RBC.

When it no longer functions does it change? yes.

Therefore I agree with the person above who characterizes the blood cell as functioning or not functioning.