Red blood cell

Red blood cells, also called erythrocytes, are the most common type of blood cell in our bodies. They carry oxygen from the lungs to all the tissues and organs, helping them work properly. This is important because our cells need oxygen to stay alive.

Red blood cells are special because they are filled with a substance called hemoglobin. Hemoglobin contains iron and gives blood its red color. It also grabs oxygen from the air we breathe and drops it off where it’s needed in the body.

In humans, red blood cells are flexible and shaped like very thin disks. They don’t have a nucleus, a special part found in most cells, so they can hold more hemoglobin. Our bodies make about 2.4 million new red blood cells every second! These cells travel through our blood for about one to two months before they are recycled.

Structure

Vertebrates

Most animals with backbones, like mammals and humans, have red blood cells. These cells help carry oxygen through the blood. The only known animals with backbones that don’t have red blood cells are crocodile icefish. They live in very cold, oxygen-rich water and carry oxygen differently.

Red blood cells contain a special material called hemoglobin, which helps carry oxygen. Hemoglobin picks up oxygen in the lungs or gills and releases it into the body. It also helps carry some carbon dioxide, a waste product, back to the lungs.

Mammals

In mammals, red blood cells are usually shaped like flat, flexible disks. This shape helps them move easily through tiny blood vessels and allows them to release oxygen well. Some mammals, like camels and deer, have different shapes for their red blood cells.

Mammalian red blood cells lose their nuclei when they mature. This gives more space for hemoglobin, which is important for carrying oxygen.

Human

A typical human red blood cell is very small, about the size of a tiny dot. Adults have many red blood cells at any time, and these cells give blood its red color and help carry oxygen throughout the body.

Microstructure

Red blood cells in mammals do not have a nucleus when they are fully grown. This means they are "empty" inside, unlike red blood cells in other animals, which do have nuclei. Without a nucleus, red blood cells can be smaller and fit easily through tiny blood vessels.

The outside of red blood cells has a special layer called a membrane. This membrane has three parts: a sugary coating on the outside, a middle layer made of fats and proteins, and a network of proteins on the inside. These parts help the cell stay flexible, stick to other cells when needed, and work with the body’s defense system. The fats in the membrane help control what can pass through the cell and keep the cell strong.

Function

Red blood cells help carry oxygen and carbon dioxide in your body. They pick up oxygen from your lungs and take it to your tissues. They also move carbon dioxide from your tissues back to your lungs to be breathed out.

Besides carrying gases, red blood cells have other important jobs. When they go through small blood vessels, they release chemicals that help keep the vessels open. They also help control blood flow to places that need more oxygen. Red blood cells can help fight some germs by breaking down their walls.

Life cycle

Human red blood cells are made through a process called erythropoiesis. They come from special stem cells and take about 7 days to grow up. Once they are grown, these cells stay in our blood for around 100 to 120 days. In babies, this time is a little shorter, about 80 to 90 days.

Red blood cells are always being made in the red bone marrow of big bones. A special hormone called erythropoietin, made by the kidneys, can tell the body to make more of them. As red blood cells get older, they change and are taken out of the blood by certain cells in the body, which helps keep the blood healthy and balanced.

Clinical significance

Disease

Blood diseases that affect red blood cells can cause there to be too few of them or make them not work right. This can mean less oxygen reaches the body’s tissues. One common example is when the body does not get enough iron. Iron helps make a substance called hemoglobin that carries oxygen. Another example is when the body cannot absorb a vitamin called B₁₂. This vitamin is important for making red blood cells. Some people are born with conditions that make their red blood cells have unusual shapes. This can make it hard for blood to flow properly. There are also diseases where the body’s bone marrow does not make enough red blood cells.

Transfusion

Red blood cells can be given to people who need them through a process called a blood transfusion. The blood can come from another person or be stored from the patient’s own blood taken earlier. Before giving blood, it is tested to make sure it is safe and matches the patient’s blood type. This helps prevent problems during the transfusion. Red blood cells are often given to people who have low levels of these cells, are bleeding, or are about to have surgery where they might lose blood. Scientists are also working on making red blood cells in laboratories that could be used for transfusions in the future.

Tests

Doctors use blood tests to check red blood cells. These tests can count how many red blood cells there are, measure how much of the blood is made up of these cells, and determine a person’s blood type. Looking at a small sample of blood under a microscope can help diagnose diseases affecting red blood cells.

Separation and blood doping

Red blood cells can be separated from the rest of the blood using a process called centrifugation. This is used in medical treatments where only red blood cells are needed. Some athletes have tried to improve performance by storing their own red blood cells and putting them back into their bodies before competitions. However, this practice can be dangerous and is not allowed.

History

The first person to describe red blood cells was a young Dutch biologist named Jan Swammerdam. He used an early microscope in 1658 to look at the blood of a frog. Later, in 1674, Anton van Leeuwenhoek described them in more detail and guessed their size.

In 1901, Karl Landsteiner found the three main blood groups—A, B, and C, which he later called O. He showed how these blood groups act when mixed. Two of his friends found a fourth blood group, AB, the next year.

In 1959, Max Perutz found the shape of hemoglobin, the protein in red blood cells that carries oxygen, using X-ray crystallography.

The oldest intact red blood cells ever found were in Ötzi the Iceman, who lived around 3255 BCE. These cells were found in May 2012.