Gross Anatomy of Bone: Bone Marrow - Online Tutor, Practice Problems & Exam Prep

Bone marrow consists of two types: red marrow, responsible for hematopoiesis (the formation of blood cells), and yellow marrow, which stores triglycerides (fat). In adults, red marrow is found in spongy bone, while yellow marrow predominates, located in both spongy bone and the medullary cavity of long bones. Red marrow produces platelets, red blood cells, and white blood cells, crucial for maintaining blood health. As individuals age, yellow marrow can revert to red marrow if increased blood production is needed, highlighting the dynamic nature of bone marrow's function.

Bone Marrow

We've previously said that the inside of bone is filled with all sorts of different little spaces, but, of course, those spaces aren't just empty. They're filled with something, and what they're filled with is bone marrow. We're going to talk about bone marrow in a lot more detail here. So we'll just start out by saying that there are going to be 2 types of tissues that fill the space inside of bone, and those types of tissue are going to be the red marrow and the yellow marrow. Now, we'll start with red marrow.

Red marrow is just going to be the site of hematopoiesis, and hematopoiesis is just a long, kind of difficult to pronounce word that means the formation of blood cells. And you're probably familiar with that as a function of bone marrow. Most people, if you ask them what does bone marrow do, they know that it produces blood. If you're thinking about that as a function of marrow, you are thinking about red marrow. Now red marrow is going to be found only in spongy bone in adults.

Now importantly, not all spongy bone is filled with red marrow, but if you're looking for red marrow, you've got to look in the spongy bone. And red marrow is going to be the primary marrow type in babies. When a baby is born, they really only have that red marrow to produce a lot of blood because they're growing. And as you age and get older, you don't need to be making as much blood all the time, so more and more of your marrow becomes yellow marrow. We'll talk about that in just a second.

First, I want to look down at this picture, though. So, we have the end of the femur here, and we're looking at it in cross section. And if we look up at the end of the femur, where it's all red, that's the spongy bone, and it's filled with that red marrow. And it's showing us what it's doing here. It has a factory

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This little cartoon of the factory used to think, well, what is that red marrow making? Well, what's coming out of the factory? We have platelets, red blood cells, and white blood cells. All our blood cells are being made in that spongy bone in the red marrow. So, onto the yellow marrow.

Yellow marrow is going to be the site of triglyceride or just fat storage, and it's yellow because fat is kind of yellowish in color. This is going to be found in spongy bone, but it's also going to be found in that medullary cavity of a long bone. Now, we haven't defined the medullary cavity yet, but the shaft of a long bone, you may know, is going to be hollow and filled with bone marrow. That hollow space is the medullary cavity, and we're going to talk about that in more detail in a coming video. So when you think of bone marrow, a lot of people know that if you crack open a long bone, you can see that marrow.

When you crack open a long bone like that or if you feed a marrow bone to your dog, for example, you are seeing the yellow marrow, and sometimes people like to eat it because it tastes good. So yellow marrow, though, we should know that it can also revert to red marrow. As you age, red marrow becomes yellow marrow, but if you need a lot of blood for some reason, some yellow marrow can go back and become red marrow and produce more blood for your body. So how much red and yellow marrow you have isn't a fixed thing. Yellow marrow is going to be the primary marrow type in adults.

So if you are an adult, most of your marrow is yellow marrow. Now to illustrate this, again, we see the femur, and down here in the shaft of the bone, it's colored yellow for that yellow marrow, and we see a refrigerator. And that refrigerator is supposed to illustrate that it's holding all sorts of nutrients. And we can see all sorts of good foods in here. Well, it's mostly meat and cheese, and I'm vegan, so I wouldn't eat that.

But you get the idea. There are some fat cells on the bottom. It's storing nutrients for your body. Okay. So remember, red marrow, hematopoiesis, produces blood found in spongy bone. Yellow marrow stores nutrients in the form of fat found in spongy bone and the medullary cavity. And with that, I'll see you in the next video.

Gross Anatomy of Bone: Bone Marrow Example 1

This example tells us that Priyanka is informed that she has the bone disorder myelodysplastic syndrome, and she needs a blood transfusion. Based on this information, what type of bone marrow do you think is affected in myelodysplastic syndrome? And explain your reasoning. Alright. Based on this information, there's not a lot of information present.

There's myelodysplastic syndrome, and she needs a blood transfusion. Myelodysplastic, that's a complex word. I'm not going to worry about what it means or how to break it down because we have this information about a blood transfusion, which is significant. To remind ourselves of this, we have a femur depicted over here on the right. This picture shows a femur at the epiphysis, which is colored red to represent red marrow. Out of this, an arrow points out that all these different types of blood cells—red blood cells, white blood cells, and platelets—are produced there.

In contrast, the diaphysis is portrayed in yellow, indicating yellow marrow, and there we have adipose tissue or storage of fat triglycerides. Just knowing this, knowing that someone needs a blood transfusion, it indicates it must be related to the red marrow. So, I'm going to write down red marrow, and my reasoning is that the condition concerns blood. Of course, not all blood conditions have to deal exclusively with red marrow, but if it pertains to the type of marrow being affected, it's likely to do with the red marrow.

Myelodysplastic syndrome is actually a group of disorders that affect the proper development of blood cells. With that, we have more practice problems to follow, and I'll see you there.

Which of the following could be a reason why babies have relatively more red marrow than adults?

• A. Babies require red blood cells to be produced quickly to accommodate growth.
• B. The red marrow will aid in heat production keeping babies warm.
• C. Red marrow is located in spongy bone and babies' bones need to be softer than adults'.
• D. The triglycerides in red marrow aid in brain development.

In 1820, George Pollard and Charles Ramsdell were rescued after 93 days at sea in a small whaling boat after a sperm whale charged and sank their ship in what would become the inspiration for the novel Moby Dick. The two men were found adrift, sucking on the broken long bones of their dead shipmates. What nutrients were they receiving by sucking on the bones?

• A. Glucose and glycogen from the marrow.
• B. Triglycerides from adipose tissue.
• C. Protein and amino acids from epithelial tissue.
  
• D. NaCl from the bone matrix.

Here’s what students ask on this topic:

What is the primary function of red bone marrow?

The primary function of red bone marrow is hematopoiesis, which is the formation of blood cells. This includes the production of red blood cells, white blood cells, and platelets. Red marrow is crucial for maintaining blood health and is predominantly found in the spongy bone of adults. In infants, red marrow is more widespread, reflecting their higher need for blood cell production due to rapid growth. As individuals age, some red marrow converts to yellow marrow, but it can revert back if increased blood production is needed.

Where is yellow bone marrow found in adults?

In adults, yellow bone marrow is primarily found in the medullary cavity of long bones and also in some spongy bone. The medullary cavity is the hollow central part of the shaft of long bones. Yellow marrow stores triglycerides (fat), which serve as an energy reserve. While red marrow is responsible for blood cell production, yellow marrow's main function is nutrient storage. However, yellow marrow can revert to red marrow if the body requires increased blood cell production.

How does bone marrow change from infancy to adulthood?

In infancy, bone marrow is predominantly red, reflecting the high demand for blood cell production to support rapid growth. As individuals age, a significant portion of red marrow converts to yellow marrow, which stores fat. By adulthood, most bone marrow is yellow, found in the medullary cavity of long bones and some spongy bone. However, the body retains the ability to convert yellow marrow back to red marrow if increased blood production is needed, demonstrating the dynamic nature of bone marrow.

Can yellow bone marrow revert to red bone marrow?

Yes, yellow bone marrow can revert to red bone marrow if the body requires increased blood cell production. This process is essential during situations like severe blood loss or certain diseases where the demand for new blood cells rises. The ability to switch between yellow and red marrow highlights the dynamic and adaptive nature of bone marrow, ensuring that the body can meet its hematopoietic needs as required.

What types of cells are produced by red bone marrow?

Red bone marrow produces three main types of blood cells: red blood cells (erythrocytes), white blood cells (leukocytes), and platelets (thrombocytes). Red blood cells are responsible for carrying oxygen throughout the body. White blood cells play a crucial role in the immune system by fighting infections. Platelets are essential for blood clotting and wound healing. This production process, known as hematopoiesis, is vital for maintaining overall blood health and function.