ELI5- What are blood groups? Why do they differ from person to person? Why can’t a person of one blood group receive blood from a person of a different blood group?

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In: Biology

20 Answers

Anonymous 0 Comments

There are four groups of blood types, A, B, AB, and O. They can all be positive, or negative.

what makes you fall in one of the groups is whether or not you have A and/or B antigens, or none of them:

> A type blood has only A antigens on red blood cells
> B type blood has only B antigens on red blood cells
> AB has both A and B antigens on red blood cells
> O has neither A nor B antigens on red blood cells

As for the plus or minus, that depends on if you have a protein called RhD on your red blood cells (positive meaning you have it, negative meaning you don’t).

The way blood can be transferred works like this: You can only receive blood from blood types that don’t have any antigens you don’t have. So, O can give to any type, A and B can give to AB and their own types, and AB can give to only themselves.

On top of that though, while negative blood types can give to both positive and negative blood, positive blood cannot transfer to negative. So, while O- can give to literally any blood type, O+ can only give to positive ones.

Anonymous 0 Comments

They’re basically genetic markers that you have in your blood.

If the donor has a marker that the recipient doesn’t have the body will detect it as foreign and the immune system will attack. Which can cause blood clotting, kidney failure, pain all over, breathing problems (and possibly death)…all the bad stuff that can happen when bloodcells are breaking down inside your body.

Even if you have the same bloodtype you might still get an allergice reaction, which is why doctors always perform a compatibility test before doing a transfusion.

As for why they’re different? Some people are tall, some people have red hair, some people have brown eyes, some people have AB+ bloodgroups. There is really no reason except that at some point someone got the genetics for these markers and then their kids got them etc.

Anonymous 0 Comments

Your blood cells have little markers on them that say ‘I belong to this body’

If you give someone blood with the wrong tag, then your immune system starts attacking the other person’s blood thinking it’s an invader causing an allergic reaction. Which is bad.

Anonymous 0 Comments

In some blood types, it’s like the blood cells are wearing little hats. If you get some blood cells wearing hats and you don’t normally have them, your body is like, whoah, these shouldn’t be here, and it attacks them. Type A only likes type A hats, and type B only likes type B hats. Type AB is cool with either kind of hat. Type O doesn’t have any hats itself, so the bodies of Type O people will attack A or B or AB blood cells. People with A, B, or AB blood types are ok receiving the hatless Type O blood cells.

The positive and negative refers to Rh blood types. Rh blood types are like the cells have mustaches. Rh+ types, they’ve all got mustaches but they’re ok accepting blood cells with no mustaches. Rh- types, they don’t want any of those stupid mustaches. Maybe they could tolerate it a bit, if it’s an emergency, but really no mustaches would be better. So an AB+ person is cool with blood that has any kind of hat and mustaches or no mustaches, so they can take any kind of blood, while an O- person can only accept blood with no hats and no mustaches.

There are other accessories that affect blood type, representing more detailed blood types. For surgery and stuff usually ABO type and Rh type are all that matters, but for some transplants you really need the closest type possible, like blood with the exact same hat and facial hair and jewelry and clothes and haircut. That’s why people who need kidneys or bone marrow will sometimes ask lots and lots of people to check if they’re a potential match, and maybe never find anyone.

Anonymous 0 Comments

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Anonymous 0 Comments

What about Rh+ and RH-? What do those mean?

Anonymous 0 Comments

Your cells respond to each other by producing proteins. A significant part of the immune system works by detecting proteins that cells display on their surface like a kind of braille. Your immune cells literally creep up on your blood cells (and all other cells) and ‘feel’ this braille to see if the cell is doing what it is supposed to be doing. This is how they can detect foreign objects, bugs like bacteria, and things like cancerous cells (most people actually develop ‘technically cancer’ at multiple times in their lives and their immune system just deals with it without them ever noticing, ‘actual cancer’ is the result of several things going wrong at once!).

Your ‘blood group’ then is a kind of protein that blood cells display on their surface. I think why these exist is beyond ELI5 (to do with sorting of cells during development in the womb I think?), but basically it turns out that between humans these proteins are fairly similar between people, there are only two types! A and B, how easy is that!? You then also have some people who don’t express either of these, which we call O. Because your immune system uses these proteins to recognize that the blood cell is actually *you* and not something foreign, this is quite convenient as the system is dumb enough for us to trick it. So long as the immune system is feeling this same braille pattern on the blood cell, it can’t *actually* tell where that cell come from it just moves along.

So then why people fall into different groups is kind of a separate question to do with genetics that others have kind of already answered, to do with what blood group proteins your parents express.

You also have the ‘positive’ and ‘negative’ rhesus blood groups, which is the same principle as the A/B/O blood group types, but another protein braille pattern that’s being felt.

Anonymous 0 Comments

Think of it as mixing colors. Your blood can be tagged as either Black, white, red, blue, yellow, green, purple or orange.

If you are “red”, you can donate to other red, orange, purple, or white. All of those “include red”.

If you are “green”, you can receive from green, blue, yellow and black. None of those “add” a color to your green.
But if you donate to someone who’s blue, you poison him with the yellow in your green.

If your color is white, you can accept anything (universal receiver), but will poison anyone who isn’t also white.

And if your blood is black, you can’t poison anyone (universal donor) but any blood that isn’t black will poison yours.

Anonymous 0 Comments

The blood cells each contain a code on them somewhat like a key, this key only lines up with certain ‘locks’ in the body. This key can be used for your body to identify friendly blood cells from foreign ones. ( the body is hella xenophobic for obvious reasons)
Basically if the body recognizes a cell that is foreign (fungus, bacteria, anything without the key) it sends the security guard cells (WBC/phagocytes) to go and surround the foreign invader to keep it from causing trouble, eventually killing it.
If you where to trade blood with a person of a certain type of blood (ie You are A+ and he is B-) then your body would have bad reaction and you would likely die.
The A part is one part of the key, the + part is a separate part. If the receiving locks do not match either of these you will have a bad time.

Anonymous 0 Comments

There are lots of different blood groups, ABO and Rhesus D are the most commonly known. Your red blood cells which carry oxygen have little markers all over them called antigens. A group A person’s red cells have A antigens, a group B person’s red cells have B antigens, a group AB person’s red cells have A and B antigens and a group O person has neither A or B antigens. People will naturally have antibodies in their plasma (the liquid part of blood) which are produced by white cells (the immune cells that protect the body) to the antigens that they don’t have. So Group A will have Anti-B antibodies, Group B will have Anti-A antibodies, Group O will have Anti-A and Anti-B antibodies and Group AB will not have either Anti-A or Anti-B antibodies. These antibodies when they detect antigens that they are specific for will stimulate the immune response to destroy these cells. That’s why if you give a Group O person Group A red cells their immune system will attack the new cells that their immune system recognises as foreign and they will have a transfusion reaction which can be fatal. Transfusing people red cells from the same ABO group as they are prevents the persons immune system from realising that these new cells introduced are foreign, preventing a reaction.

Rhesus D and also Kell are the two most immunogenic antigens of all the other blood group families. Immunogenic means the most likely antigens the person’s immune system receiving foreign red cells will recognise as foreign and create antibodies against if the individual receiving the red cells doesn’t have these antigens on their own red cells. Antigens being recognised as foreign and the immune system creating antibodies is known as sensitisation. This is typically not dangerous the first time as is the case with allergies. The first attack by the body is weak because its ‘defenses’ weren’t ready. The second time the person is exposed to the foreign antigen the immune system will rapidly spring into action to destroy the foreign cells causing a more serious transfusion reaction that can be life threatening. As a general policy people who are rhesus D negative are only given Rhesus D negative units to prevent sensitisation and women of child bearing years and children are always given Kell negative units also to prevent sensitisation. Any unit of red cells will always have these 3 pieces of information on them; ABO group, Rhesus family status and Kell type.