Erythrocytes - Online Tutor, Practice Problems & Exam Prep

Erythrocytes, or red blood cells, are small, biconcave, anucleate cells crucial for gas transport, specifically oxygen and carbon dioxide. Their unique shape enhances flexibility and surface area, facilitating efficient gas exchange. Packed with hemoglobin, erythrocytes can adapt to narrow capillaries, folding to pass through and returning to their original shape in larger vessels. The cytoplasmic protein spectrin maintains their structure, highlighting the relationship between cell structure and function in the cardiovascular system.

Structure of Erythrocytes

In this video, we're going to talk about the structure of erythrocytes. And so erythrocytes, red blood cells, or RBCs are relatively small cells in comparison to most other body cells. In fact, they're about 3 times smaller than most other body cells, so that's a pretty notable fact. Also, these erythrocytes, or red blood cells, are biconcave shaped, which really just means that they are flattened discs, as you can see here, with a depressed center. And so notice that we're showing you a cross section of the red blood cells that you can see that biconcave shape even better. And notice once again that they are a flattened disc with a depressed center. And so really, the biconcave shape of these red blood cells is very similar to the shape of a donut, because they are both flattened discs with a depressed center. However, most donuts have a complete hole going through the middle of them, whereas that's not the case with these red blood cells. The red blood cells only have a depressed center, not a complete hole going through the middle.

Now, these erythrocytes or red blood cells are different than most other body cells in that they lack a nucleus. And so, these erythrocytes or red blood cells are considered anucleate since they do not have a nucleus. They also lack many organelles as well, including mitochondria, endoplasmic reticulum, and Golgi apparatus, among others. The structure of these erythrocytes, or red blood cells, is going to be highly linked to its function, which recall from our previous lesson videos that the main function of these erythrocytes or red blood cells is gas transport, oxygen gas, and carbon dioxide gas transport. The biconcave shape of these erythrocytes increases the red blood cells' overall flexibility so that they can fit into really tight and narrow spaces, and the biconcave shape also increases the red blood cell's surface area to volume ratio, which is critical to help maximize the efficiency of gas exchange and transport.

Again, it's the structure that's going to help dictate the function. These erythrocytes or red blood cells also have a meshwork of cytoplasmic proteins, including a family of proteins known as spectrin. Spectrin is going to help maintain the red blood cell's shape. What's important to note is that these erythrocytes, or red blood cells, are often going to need to fit into really tiny blood vessels or capillaries, where the red blood cells themselves are actually bigger and wider than those blood vessels. This means that the red blood cells often need to fold up on themselves and bend in order to fit through the tight and narrow spaces of the capillaries. However, when those red blood cells get back into a larger vessel with more space, those red blood cells will spring back into their original biconcave shape. Again, it's these cytoplasmic proteins like spectrin that help to maintain the red blood cell shape.

A very important fact to note about red blood cells is that they are packed with tons and tons of hemoglobin, which can be abbreviated as HB. This hemoglobin is really just a protein that functions in gas transport, specifically oxygen and carbon dioxide gas transport. As we move forward in our course, we'll get to talk more about the structure and function of the hemoglobin molecule. But for now, what you should note is that each individual red blood cell is packed with tons of hemoglobin protein.

Let's take a look at our table down below so that we can differentiate between erythrocytes on the left and most other body cells on the right. The first thing that you'll notice is that erythrocytes are quite small in size in comparison to most other body cells. In fact, the diameter of the erythrocyte is about 7 and a half micrometers, whereas most other body cells are going to be larger in size and have a diameter that is about 25 micrometers. Again, most other body cells are about 3 and a half times larger than erythrocytes. In terms of their shape, erythrocytes are biconcave, which means that they have this flattened disc with a depressed center, whereas most other body cells do not have a biconcave shape. Erythrocytes also lack a nucleus, so they are anucleate. They also lack many organelles, such as mitochondria, endoplasmic reticulum, and Golgi apparatus, for example. Whereas most other body cells do contain a nucleus and also contain these organelles. Again, erythrocytes are coated with flexible proteins such as spectrin, which helps them to maintain their shape even after they squeeze through tiny blood vessels and have to fold up and bend, whereas most other body cells are not going to be coated with those spectrin proteins. And last but definitely not least, erythrocytes are going to be packed with tons of hemoglobin protein molecules, which again are going to function in gas transport, oxygen, and carbon dioxide gas transport. Whereas most other body cells are not going to be packed with those hemoglobin proteins. This concludes our brief lesson on the structure of erythrocytes. As we move forward in our course, we'll be able to learn more. So I'll see you all in our next video.

Erythrocytes Example 1

Here we have a pretty straightforward example problem asking, which of the following statements about erythrocytes is false? And we've got these 4 potential answer options down below. Option A says they use mitochondria to make their own ATP. B says they are smaller than the average body cell. C says their shape is flexible, and D says they don't have a nucleus. Now, of course, recall from our last lesson video that erythrocytes, or red blood cells, lack a nucleus and many organelles, including mitochondria. And so erythrocytes don't have mitochondria, and to say that they use mitochondria to make their own ATP is simply a false statement. Again, because they don't have mitochondria, and so they have to use other means to make their own ATP.

And so what this means is that answer option A is the false statement that we are looking for. So we can indicate that A here is the correct answer to this problem, and these other statements that we see down below are all true statements. It's true that erythrocytes are smaller than the average body cell. In fact, they're about 3 times smaller than the average body cell, which is pretty significant. It's also true that their shape is flexible. They have a biconcave shape that increases their flexibility. They lack a nucleus and many organelles, which also adds to their flexibility since that helps them be able to bend and fold easier. They also have proteins such as spectrin, which increases their flexibility and helps them maintain their shape even after they have to fold and bend through tiny blood vessels and capillaries, and when they get back into a larger space, they can spring back into their original shape because of those proteins.

Also, erythrocytes don't have a nucleus, and so they are considered anucleate. So again, option A is the correct answer to this problem. Now it is interesting to think, what if erythrocytes did have mitochondria? Well, recall from previous videos that mitochondria use or consume oxygen to make ATP. And erythrocytes play a huge role in delivering oxygen to tissues. And so if erythrocytes did have mitochondria, they would be consuming some of the oxygen that they were supposed to be delivering to the tissues, and so that would be similar to a pizza delivery guy taking a bite out of one of the slices before they deliver it to you. It's simply not going to work, and so thankfully, our erythrocytes have evolved to dispose of their mitochondria. And so again, this concludes this problem. Option A is the correct answer, and I will see you all in our next video.

What is the primary function of the protein spectrin in erythrocytes?

• A. To allow efficient gas exchange of oxygen and carbon dioxide into and out of erythrocytes.
• B. To maintain the shape of erythrocytes and allow them to change shape when needed.
• C. To make ATP, as there are no mitochondria in erythrocytes.
• D. To hold hemoglobin molecules in place.

Here’s what students ask on this topic:

What is the structure of erythrocytes and how does it relate to their function?

Erythrocytes, or red blood cells, are small, biconcave, anucleate cells. Their biconcave shape, resembling a flattened disc with a depressed center, increases their surface area to volume ratio, enhancing gas exchange efficiency. This shape also provides flexibility, allowing erythrocytes to navigate through narrow capillaries by folding and then returning to their original shape. The absence of a nucleus and most organelles, such as mitochondria, endoplasmic reticulum, and Golgi apparatus, maximizes space for hemoglobin, the protein responsible for oxygen and carbon dioxide transport. The cytoplasmic protein spectrin helps maintain their shape, ensuring they can withstand the mechanical stress of circulation.

Why do erythrocytes lack a nucleus and most organelles?

Erythrocytes lack a nucleus and most organelles to maximize their internal space for hemoglobin, the protein crucial for oxygen and carbon dioxide transport. The absence of these structures allows erythrocytes to carry more hemoglobin, enhancing their gas transport capacity. Additionally, the lack of a nucleus and organelles reduces the cell's metabolic demands, making erythrocytes more efficient in their primary function of gas exchange. This streamlined structure is essential for their role in the cardiovascular system, where they need to be highly efficient and flexible to navigate through narrow capillaries.

How does the biconcave shape of erythrocytes enhance their function?

The biconcave shape of erythrocytes enhances their function by increasing their surface area to volume ratio, which is critical for efficient gas exchange. This shape allows for more hemoglobin molecules to be exposed to the cell membrane, facilitating quicker oxygen and carbon dioxide transport. Additionally, the biconcave shape provides flexibility, enabling erythrocytes to deform and pass through narrow capillaries. Once they exit these tight spaces, they return to their original shape, thanks to the cytoplasmic protein spectrin, which maintains their structural integrity.

What role does hemoglobin play in erythrocytes?

Hemoglobin is a protein found in high concentrations within erythrocytes, playing a crucial role in gas transport. Each hemoglobin molecule can bind to oxygen and carbon dioxide, facilitating their transport throughout the body. Hemoglobin's ability to bind and release these gases efficiently is essential for maintaining proper oxygen levels in tissues and removing carbon dioxide, a waste product of cellular respiration. The high concentration of hemoglobin in erythrocytes maximizes their capacity to transport these gases, making them highly efficient in their primary function.

What is the function of the cytoplasmic protein spectrin in erythrocytes?

The cytoplasmic protein spectrin plays a vital role in maintaining the shape and structural integrity of erythrocytes. Spectrin forms a meshwork beneath the cell membrane, providing mechanical support and flexibility. This allows erythrocytes to deform as they pass through narrow capillaries and then return to their original biconcave shape once they enter larger blood vessels. By maintaining the erythrocyte's shape, spectrin ensures that the cells can efficiently perform their gas transport function without being damaged during circulation.