Have you ever wondered what your blood does for you? Or how your body has the ability to stop a cut from bleeding? Blood is a pretty special substance in our bodies. It has many special responsibilities, the most important one being carrying oxygen to all of the cells in our body, so they can continue to do their jobs, and then carrying carbon dioxide (CO2) to the lungs so we can breathe it out. Blood also has many different parts to it, beyond just the red blood cells that everyone usually knows about. On the surface, blood seems like a pretty simple substance with a pretty simple job; the more you learn about it, however, the more you see just how much blood does to keep our bodies running, helping show how important of a substance it really is. 

There are two major parts to blood: cells and plasma. Cells make up around 45% of our blood, and plasma makes up around 55%. When looking at blood that comes out of a cut, all we see is red. This substance is a mix of cells and plasma. When we spin tubes down, though, we can see that the cell section is at the bottom of the tube, and is in two sections: red and white. The plasma section is at the top and is a yellow, straw-colored liquid. Cells settle at the bottom of the tube because they’re denser than the plasma. As tubes are spun down in special machines called centrifuges, the different sections of blood split up into these distinct areas. In this article, we are going to talk all about the cells that are in blood; check out the next article for all things plasma-related! 

The cell section is composed of three different main types. There are red blood cells, white blood cells, and platelets. Each type of cell has a different look and each does a different, important job to keep our body running properly.

Red Blood Cells (RBCs, also called Erythrocytes)

RBCs look like circular discs that concave (dip) in their centers. They do not have any organelles within their cell wall; this makes them different from every other kind of cell in the body. The only thing inside their cell membrane are structures called hemoglobin. These structures help RBCs accomplish their one major job. RBCs are responsible for bringing oxygen from the lungs to all of the cells of the body, and to take carbon dioxide from the cells and bring it back to the lungs so we can expel it. The hemoglobin within grips onto the oxygen molecules we breathe in, and hold on to them until the RBCs make it to their destination. Once they reach their end spot, the hemoglobin lets go and passes the oxygen from the RBC into the desired cell. This cell then trades its carbon dioxide for the oxygen. After this trade happens, the RBCs travel back through the body until it reaches the lungs again, and makes another trade- this time trading CO2 for another oxygen molecule. After this trade is complete, the cycle begins again. 

This cycle of taking oxygen to cells and returning CO2 to the lungs continues over and over for 90-120 days. At this point, RBCs have been doing this cycle so much they become old and sometimes damaged. When RBCs cannot do their job correctly, they are taken out of the circulation and moved to the spleen. Once they reach the spleen, the cells are broken down into their different parts and recycled to help the body do other important functions. But don’t worry- as old cells are taken out of circulation, brand new cells are entering it from the bone marrow. The new cells take over for the old cells, keeping the oxygen-CO2 cycle running smoothly.  

White Blood Cells (WBCs, also called leukocytes)

Another important kind of cell in blood is the white blood cell, WBC. White blood cells are very important for keeping our immune system healthy and functioning. When we get sick, WBCs step in and fight the invaders on the inside. WBCs are a little more complicated than RBCs. Red blood cells only have one kind; they all have the same shape and the same structures inside. White blood cells, on the other hand, have five main kinds of cells, all with different looks and different functions. Listed below are the five most common types of WBCs seen, and a little about how they fight to keep our bodies safe and protected. 

Neutrophils (50-70%)

• Neutrophils are the body’s first line of defense when something is found that shouldn’t be there. They aren’t picky when it comes to attacking invaders; they jump in and start defending our body against anything!

Basophils (0-2%)

• Basophils are key players in allergic reactions. When a person has a reaction to something, like peanut butter or bee stings, basophils are called to help out. Basophils release two important chemicals to help the body fight against the allergen.

Eosinophils (1-5%)

• Eosinophils are easy to pick out because of their unique color- they’re orange! And they have big purple dots inside. These cells have a similar effect as Basophils, except they are summoned when the body detects a parasite rather than an allergen. 

Monocytes (1-6%)

• Monocytes are big cells! Their main job is to “eat” up harmful substances in the body. They do this by a process called phagocytosis- “cell eating”. So Monocytes “eat” a bacteria or virus by bringing it inside its cell membrane, then breaks it down and stops it from harming the body. 

Lymphocytes (20-40%)

• Lymphocytes have two main types, B-cells and T-cells. B-cells are made in bone marrow, and are called on when the body detects a certain structure (antigen) that is foreign to the body. B-cells help make antibodies that attack the antigen. T-cells are made in the thymus and are called on mainly when there’s a viral infection or if cancerous cells are detected. T-cells can also help B-cells, if needed. 

Platelets (also called thrombocytes)

Last, but certainly not least, are platelets. Platelets are fragments of cells that are broken off of very large cells called megakaryocytes. Megakaryocytes are found in bone marrow; as platelets break off of this cell, they are released from the bone marrow and sent into circulation. Once in circulation, platelets have one very important job: they help your blood clot. When you get a cut or a scrape, it usually bleeds for a little bit and then eventually stops. Platelets are what helps the cut stop bleeding. When a cut is detected, there are three steps the body goes through to stop the bleeding. 

• First- the blood vessels around the cut are constricted, or squeezed, to make less room for blood to flow. With less room for blood flow, the cut starts bleeding less.

• Second- platelets are sent through the blood vessels to the area that was injured. Once they arrive, they start to form a platelet plug around the cut. Platelets also release different substances into the bloodstream in order to get more platelets sent to the area so the plug can be formed faster. 

• Third- the blood starts to clot, meaning it forms a glue-like substance that helps hold the platelet plug in place so all bleeding stops. Once bleeding stops, the body can start to repair the cut.

The cells in our blood all have very important, very different responsibilities in order to help keep us healthy and functioning. RBCs are responsible for making sure oxygen reaches our cells, and CO2 leaves cells. WBCs are responsible for fighting any type of sickness or infection that is detected in the body. Platelets are used to help the body stop bleeding from any cut that may form. All of these cells are incredibly important in our bodies, and thankfully we have millions of them floating around, waiting to be called upon to help make our bodies work as best they can. 

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