BLOODY USEFUL CELLS MAKING UP YOUR BLOOD

You know what your blood looks like.. it's red! Right? Unless maybe if you're a royalty.. Just a plain red liquid. Or is it? Have you ever considered what it would look like under a microscope? Or how the immune system actually does its thing? Or where it even is?

You're lucky - we have the answer to all those questions and more! Join us on a fascinating adventure into your veins!

The blood is made up of three main components: the plasma (55%), red blood cells (44%), and white blood cells (1%). The plasma is the actual liquid part of the blood and helps with the transportation of blood cells, nutrients, and waste products around the body. The red blood cells are really important for the transportation of oxygen around the body, which is crucial for all your cells to function. The blood also has several other functions, such as temperature regulation, clot formation to prevent excessive blood loss following injury, and carrying cells of the immune system to sites of infection.

The white blood cells are a small but super important part of your blood as they are the cells that form your immune system and protect you against diseases using a really high-tech defence system. All of the immune cells are born in the bone marrow from a common stem cell which is able to divide and form different types of immune cells. There are two main types of immune cells: myeloid and lymphoid. In general, myeloid cells remain in the bone marrow or migrate to your organs, while the lymphoid cells (lymphocytes) move to the lymph nodes. Myeloid cells include cells like platelets, neutrophils, monocytes, and macrophages which are generally part of the initial, rapid, but non-specific immune response. The lymphoid cells include T cells and B cells which make up your highly specific and long-term (adaptive) immune response. As an exemption to the rule, natural killer cells are lymphocytes which are part of the innate response. Meet all these guys down below!

Selected members of the white blood cell family:

MONOCYTES

Monocytes are the largest white blood cells. They are a type of myeloid cell which is important for the innate immune response. When the monocytes leave the bone marrow, they circulate in the bloodstream for one to three days before they move into tissues throughout the body. Once in the peripheral tissues, such as your skin, they can develop into macrophages or dendritic cells. Both macrophages and dendritic cells are phagocytes (phago- = eating), cells which can engulf bacteria, viruses, and infected cells to clear them away from the body. Once engulfed, enzymes and toxic peroxides inside the phagocyte digest and kill the pathogen. This is an important part of the innate immune response. As they are located in the peripheral tissues, they are really the first-responders of the immune system. However, phagocytes can not distinguish certain types of bacteria or viruses, they just recognise "dangerous" from "safe" and thus, they are quick to react but don't have any memory.

Importantly, macrophages which have phagocytosed and digested a pathogen can present little pieces of it on their cell surface like trophies and in this way, they can help stimulate the adaptive immune response.

Monocle-cyte?

T CELLS

After being born in the bone marrow, the T cells move to the thymus to become fully educated, and that's where they get their "T" from. T cells are an important part of your adaptive immune response, and so, they are incredibly specific in what they attack and they can develop a very long memory. There are many different types of T cells. As their name suggests, cytotoxic T cells contain toxic substances which can be released to kill cells that have been infected with viruses or bacteria. They are real serial killers and very efficient in eliminating infections.

However, to be able to function properly, the cytotoxic T cells get some assistance from T helper cells. Because of their violent nature, it's important that the cytotoxic cells are tightly regulated and only attack foreign material and not your own body. T helper cells also provide important help to B cells so that they can develop appropriate responses.

Tea helper cell?

B CELLS

The B cells also contribute to the adaptive immune response. B cells can both be antigen presenting cells (like macrophages), which present parts of foreign material such as bacteria or parasites to T cells, and they also have their own defence strategy which is secretion of antibodies. Antibodies are Y-shaped molecules which are released from B cells ("B" for bone marrow), and each B cell produces a unique type of antibody. This means that within your body, you have antibodies against many different types of viruses and bacteria. The antibodies can for example coat viruses to make the harmless, and to make them more visible for macrophages, which can then engulf and digest the virus to remove it from the body.

Antibodies are also critical for the function of vaccinations. When you get a vaccination, a part of a virus or bacterium is injected into your body, and this can be recognised by B cells which start to produce antibodies with specificity for the virus or bacteria you're getting vaccinated against. This means that when you next encounter the real bug, you already have a protection in place which gets a head start, and most likely you'll never even notice the infection!

Bee cell?

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