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Do Red Blood Cells Have a Nucleus? Anatomy and Purpose

Mature Human Red Blood Cells

Red blood cells, also known as erythrocytes or RBCs, are round, disc-shaped cells that carry oxygen to supply the body. Oxygen diffuses from the lungs and into the blood where it dissolves as a free molecule. Then, it enters a red blood cell and binds to a protein called hemoglobin. Hemoglobin is a carrier protein that transports and delivers oxygen to cells and tissues. It also contains a red pigment called heme that provides red blood cells with its signature color.

The term erythrocyte is derived from the Greek word erythros and the Latin ending cyte with a combined meaning of "red cell." The hallmark of a eukaryotic (ie. humans, other mammals, plants, fungi, etc.) cell is the presence of organelles. Organelles are specialized structures that perform a specific job within the cell. The most prominent and, arguably, most important organelle is the nucleus. The purpose of a nucleus is to:

  • House the genetic information of the cell
  • Control cell growth and multiplication
  • Serve as the backdrop for DNA replication
  • Regulate the synthesis of enzymes. Enzymes are proteins that help biological reactions occur.
  • Regulate cellular differentiation

Do erythrocytes have a nucleus? While immature red blood cells contain a nucleus, mature human red blood cells do not. During the maturation process, red blood cells expel their nuclei as well as other organelles. Anucleated is the term used to denote a cell without a nucleus.

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.

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  • 0:02 Not a Simple Answer
  • 0:57 What Is a Red Blood Cell?
  • 1:20 Erythropoiesis
  • 3:20 Why Expel the Nucleus?
  • 3:48 Lesson Summary
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Red blood cells are disc-shaped cells that carry oxygen to tissues and organs.

A group of red blood cells on a black background.

Red Blood Cell Production

Erythropoiesis is the body's process of making red blood cells. The adult human body has the ability to produce approximately 2.5 billion red blood cells per day, and one red blood cell has an approximate lifetime of 120 days.

Erythropoiesis occurs in many different stages over the course of a lifetime. It occurs in the:

  • Yolk sac of an early fetus
  • Liver and spleen during months 2-5 of gestation
  • Bone marrow from 5 months of gestation forward

There are multiple stages to erythropoiesis:

  • The process begins with hemocytoblasts, a multipotent hematopoeitic stem cell. Multipotent cells have the ability to differentiate into many different types of cells. Hematopoietic means of or relating to the formation of red blood cells.
  • Hemocytoblasts differentiate into common myeloid progenitor cells.
  • Myeloid progenitor cells differentiate into normoblasts, also known as proerythroblasts. Myeloid progenitor cells can also differentiate into a selection of white blood cells through a different cellular lineage.
  • Normoblasts lose their nucleus and a few other organelles to become reticulocytes, also referred to as an immature RBC. The process of losing the nucleus is called enucleation. The expelled red blood cell nucleus is wrapped by a plasma membrane and called a pyrenocyte. Pyrenocytes are recycled back into the body.
  • Reticulocytes lose even more organelles to become mature erythrocytes.

Erythropoiesis is governed by a hormone called erythropoietin. This hormone is constantly secreted by the kidneys to maintain regular red blood cell turnover; however, secreted concentrations will fluctuate based on the needs of the body. For example, in instances of low blood oxygen levels, erythropoietin secretion will increase to produce more red blood cells. In turn, this creates more hemoglobin and an increased ability to bind and deliver oxygen. Erythropoietin is also responsible for telling red blood cell precursors how and when to differentiate into their immediate cellular descendants.

Erythropoiesis is the formation of mature red blood cells.

The cellular pathway of erythropoiesis.

Why Don't Mature Red Blood Cells Have a Nucleus?

Scientists are still evaluating the process of enucleation. It is proposed that the expulsion of intracellular contents:

  • Makes room to hold additional hemoglobin
  • Allows the cells to maintain a concave disc-like shape
  • Provides red blood cells with the flexibility and malleability to maneuver through the circulatory system

Why don't red blood cells have a nucleus? Most likely, red blood cells expel the nucleus in exchange for the aforementioned physiological advantages. The absence of organelles makes more room for hemoglobin and increases its ability to carry and deliver oxygen.

Additionally, red blood cells maintain a concave center which would not be possible if the cell contained organelles. This is because there would be no additional space for the cell membrane to dip into the center of the cell. The concave surface of the cell membrane increases its surface area as well as the amount of oxygen that can be delivered to tissues and organs at one time.

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.

Erythropoiesis

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.

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Video Transcript

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.

Erythropoiesis

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.

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Frequently Asked Questions

Why don't red blood cells have a nucleus?

It is proposed that the absence of a nucleus provides more space inside the cell. More space equates to the ability to carry more hemoglobin and flexibility to maneuver through the cardiovascular system. Red blood cells also do not undergo cell division and do not depend on genetic material for cellular replication.

Do red blood cells have a nucleus?

Immature red blood cells have a nucleus while mature red blood cells do not. Mature red blood cells lose their nucleus during the process of erythropoiesis, the formation of red blood cells.

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