In this lesson, we’ll answer the question: ‘Do red blood cells have a nucleus?’ We will discuss how stages of red blood cell maturation complicate this question and come to a final answer on the topic.
Not a Simple Answer
Do red blood cells have a nucleus? Well, the short answer to this question is no.Red blood cells, or erythrocytes (erythro being Greek for ‘red’ and cyte meaning ‘cells’) are actually anucleated cells, meaning that they don’t have a nucleus. But wait! Don’t go away just yet because this is actually a much more tricky question than you would expect.Why so tricky? Well, while mature blood cells are anucleated, the precursor cells that mature into erythrocytes actually do. Kind of like a tadpole losing its tail to become an adult frog.So, the question depends on whether you are referring to a mature erythrocyte or an immature erythrocyte. Whoa- did I just blow your mind? Okay, maybe not, but it’s still pretty interesting.
Why don’t mature erythrocytes have a nucleus? That might be an even better question.
What Is a Red Blood Cell?
Let’s get some facts straight first. You might know that erythrocytes are red because of their hemoglobin, which is the protein molecule that fills the interior of the cell and is responsible for binding with oxygen. But, did you know that your blood is produced within your bones? Actually, to be specific, erythropoiesis, the production of erythrocytes, occurs within your bone marrow.
It all starts with your kidneys – that’s right, your little bean-shaped kidneys do play a role in this.
Your kidneys’ job is to filter your blood for pathogens and old erythrocytes, which need to be removed from circulation, so, in the process, they keep tabs on the general health of your blood. Kidneys secrete a hormone called erythropoietin when they sense that your blood supply is getting low based on your body’s oxygen levels. No wonder they are so important, right? Anyway, this release of erythropoietin into your blood stream in turn stimulates your bone marrow to start producing more erythrocytes.Your bone marrow houses nucleated stem cells, called hemocytoblasts, which are capable of becoming any type of blood cell – they just need direction as to which one. Now, once a hemocytoblast has been given its orders to become a erythrocyte, it becomes a proerythroblast, or a nucleated cell committed to becoming a erythrocyte – sort of like a soldier starting off under the rank of private before they can graduate into becoming a general.
The proerythroblast undergoes a series of divisions to become an erythroblast (one step closer to its final goal of erythrocyte). During this process, the nucleus decreases in size and activity while other non-essential contents of the cell shrink. When all is said and done, the erythroblast splits into two cells:
- A pyrenocyte, which is composed mostly of the condensed nucleus and is absorbed (recycled) back into your body
- A reticulocyte, which is composed mostly of cytoplasm and matures into a fully functioning, anucleated erythrocyte
This division of the cell, where the nucleus is removed from one cell rather than replicated, is called enucleation . This entire process takes about 4 days, and, since erythrocytes only live about 120 days, this process is ongoing and never-ending.
Why Expel the Nucleus?
So why expel the nucleus? Good question! Well, the function of the nucleus is to house DNA so that cells can divide and recreate themselves. However, since erythrocytes are a terminal stage cell that do not divide, the nucleus becomes a waste of space.
The big job of your erythrocytes is to carry oxygen (bound to the hemoglobin) and deliver it to the rest of the body. Therefore, if they enucleate they have more room for that oh so important hemoglobin.
Erythrocytes (erythro meaning ‘red’ and cyte meaning ‘cells’) are anucleated mature cells filled with hemoglobin (a protein molecule responsible for binding with oxygen). However, immature erythrocytes, called proerythroblasts and erythroblasts, are nucleated.
In other words, at first there’s a nucleus, later there isn’t.Erythropoiesis (the production of erythrocytes) occurs within bone marrow and is stimulated by the hormone erythropoietin. This hormone stimulates undifferentiated, nucleated, stem cells, called hemocytoblasts, to become a proerythroblast (a cell committed to becoming an erythrocyte). After many changes the cell enucleates (remove its nucleus) via dividing into two cells, one of which, the reticulocyte, will go on to mature into an anucleated erythrocyte.