Specialized Connective Tissue: Bone - Online Tutor, Practice Problems & Exam Prep

Bone tissue, or osseous tissue, is a specialized connective tissue that forms the skeleton, consisting of approximately 206 bones. It is highly vascularized, allowing for rapid healing after injury. The extracellular matrix comprises organic components like collagen fibers, providing strength and flexibility, and inorganic minerals such as calcium phosphate, contributing to its hardness. Key cell types include osteoblasts, which build bone, and osteocytes, which maintain it. Bones serve multiple functions, including structural support, protection of organs, mineral storage, and hematopoiesis, the formation of blood cells.

Intro to Bones

So, now that we've covered cartilages in our previous lesson videos, in this video, we're going to begin talking about the second type of specialized connective tissue in our lesson which is bone. Now, it's important to note that moving forward in our course in separate chapters and separate videos, we're going to talk a lot more details about bones and the skeletal system. And so here in this video, we're only going to do a brief introduction and a brief overview of some of the basics of bone tissue. And so that's important to keep in mind as we move forward. And so when it comes to bone tissue, it's important to note that it's sometimes referred to as osseous tissue.

And so, it turns out that in the human body, there are about 206 different bones. And each individual bone is its own complex living organ that needs to be able to undergo repair and remodeling in order for the bones to serve their functions. Now, we already know that bones or osseous tissues are going to be tissues with a rock-like hardness to them. We know that our bones are very very hard. Now, what's surprising to a lot of students is that bones or osseous tissues are actually very highly vascularized.

Which means that yes, our bones have lots of blood vessels. And so, when they break our bones can bleed. And so, the high vascularization of bones or osseous tissue is actually going to allow for relatively quick and complete healing of bone or osseous tissue upon being injured or damaged. Now the blood vessels actually travel through these areas known as central canals. And bone or osseous tissue is actually going to be extremely durable because bones need to support our entire bodies, and they need to be able to handle the compression forces that come with load-bearing the weight of pretty much our entire body and all of the other tissues.

Now, in terms of the extracellular matrix of bone or osseous tissue, it can actually be broken up into 2 parts. An organic part and an inorganic part. The organic part is going to include lots of collagen fibers, which we know is going to give this tissue a lot of strength and some flexibility as well. And then the inorganic part is going to include minerals such as calcium phosphate crystals. And the calcium phosphate crystals, this inorganic part, is really what gives bones its rock-hard hardness and its rock-like hardness.

And it's also what's going to give bones its rigidity and give the extracellular matrix its rigidity as well. Now, in terms of the cell types, there are 2 main cell types that we identify here that are going to be important for bones. And so it's important to note that the root osteo is a root that means bone. And so, you can find this root osteo in the 2 cell types that we identify including osteoblasts and osteocytes. Now, the osteoblasts are going to be blast cells that are going to be immature cells that are more active and actively build and secrete components of the extracellular matrix, including ground substance and protein fibers.

And then the osteocytes are going to be site cells that are more mature, less active, and are more about maintaining the extracellular matrix through minor repairs and routine maintenance. And so, these more mature osteocytes are actually going to be found in chambers called lacunae. Just like we saw cartilage chondrocytes are found in chambers called lacunae as well. And so, the lacunae are going to be chambers that house those osteocytes. Now, there is another relevant cell type in bones that we'll talk more about later in our course called the osteoclast.

And the osteoclast is going to break down bone in order to release those calcium and phosphate minerals that the body may need. But again, we'll talk about those later in our course. Now, in terms of the functions, bones actually have surprisingly a lot of different functions including the obvious function of structural support. It gives our bodies its structure and its shape. But it also allows for protection because bones such as our skull, which we know is really hard, can actually protect the delicate organs that lie underneath such as the brain, for example.

Now, bones are actually going to be important for storing calcium and other minerals such as phosphates, and they can also store fats as well inside of the bones, as we'll talk about more later in our course. And also, bones provide a cavity for a process known as hematopoiesis, which is just a fancy name for the process of blood cell formation. And so, yes, blood cells are actually formed inside of bones. Again, a process that we'll get to talk more details about later in our course. And so, notice over here what we have is an image of a person and you can see the bones that lie underneath of this person in this image.

And notice that here we have a micrograph showing you some bone or osseous tissue, and you can see that the osteocytes are these darker spots that you can see, throughout, and they are going to lie within those lacunae. And, you can also see that the central canal is being labeled as well. And again, the central canal is going to have the blood vessels which make the bone or osseous tissue highly vascularized. And so this here concludes our brief introduction to bone and osseous tissue. And again, later in our course, we'll be able to talk a lot more details about bones and osseous tissue and skeletal tissues and the skeleton in its entirety.

And so, this here concludes this video and we'll be able to apply these concepts as we move forward. So, I'll see you all in our next video.

Specialized Connective Tissue: Bone Example 1

So here we have an example problem that says, osteoporosis is a condition where the bone mass decreases making bones brittle and susceptible to fracture. Based on the structure of bone tissue, is osteoporosis caused by an issue with the osteoblasts or the osteocytes and why? Recall from our previous lesson videos that all connective tissues, including bone or osseous tissue, is going to be similar and that the cells take up much less space than the extracellular matrix. If the bone mass is decreasing, what we're saying is that there's going to be less extracellular matrix.

Recall that osteoblasts are blast cells, and blast cells are more active cells that actively secrete and build components of the extracellular matrix. Whereas, osteocytes are site cells, and they are more focused on maintaining the matrix through minor repairs and routine maintenance. Hence, the osteocytes are not going to be actively building the extracellular matrix while the osteoblasts are. With less bone mass, because that means less extracellular matrix, we can assume that this issue involves the osteoblasts.

For that reason, we can put an arrow here and indicate that osteoblasts will be our answer. Now, in reality, osteoporosis is not caused just by one type of cell. It's actually caused by an imbalance in multiple cells functioning improperly. Recall that, in addition to osteoblasts and osteocytes, we briefly mentioned that there are also osteoclasts. Osteoclasts, which we'll talk more about later in our course, are more about breaking down the bone.

Whereas, osteoblasts are more about building up the bone. It's important to have a healthy functioning balance between osteoblasts and osteoclasts in order for bones to function properly. However, osteoporosis results when there is an improper balance between osteoblasts and osteoclasts causing the extracellular matrix to become less, leading to less bone mass and making those bones more susceptible to fracture. But, the correct answer to this example problem is osteoblasts, not the osteocytes. This concludes this example and I'll see you all in our next video.

How does the ECM of bone differ from the ECM of cartilage?

• A. ECM of cartilage is flexible: ECM of bone is rigid.
• B. ECM of cartilage is rigid: ECM of bone is flexible.
• C. Bone and cartilage have the same ECM.
• D. The difference between the ECM can't be determined.

Osteonecrosis is a condition where blood flow to bones is cut off resulting in tissue death. Which of the following would you expect to be most directly affected by the loss of blood flow?

• A. The inorganic matrix.
• B. Collagen fibers.
• C. Osteocytes.
• D. A-C are correct.

Here’s what students ask on this topic:

What are the main functions of bone tissue in the human body?

Bone tissue, or osseous tissue, serves several critical functions in the human body. Firstly, it provides structural support, giving the body its shape and enabling movement by acting as a framework for muscles. Secondly, bones protect vital organs; for example, the skull protects the brain, and the ribcage shields the heart and lungs. Additionally, bones store essential minerals such as calcium and phosphate, which can be released into the bloodstream as needed. Bones also house bone marrow, where hematopoiesis, the formation of blood cells, occurs. Lastly, bones store fats in the form of yellow marrow, which can serve as an energy reserve.

What is the composition of the extracellular matrix in bone tissue?

The extracellular matrix of bone tissue is composed of both organic and inorganic components. The organic part includes collagen fibers, which provide strength and some flexibility to the bone. The inorganic part consists mainly of calcium phosphate crystals, which give the bone its rock-like hardness and rigidity. This combination of organic and inorganic materials allows bones to be both strong and durable, capable of supporting the body's weight and withstanding various forces.

What are the different cell types found in bone tissue and their functions?

Bone tissue contains several key cell types, each with specific functions. Osteoblasts are immature, active cells responsible for building and secreting components of the extracellular matrix, including ground substance and protein fibers. Osteocytes are mature cells that maintain the extracellular matrix through minor repairs and routine maintenance; they reside in chambers called lacunae. Another important cell type is the osteoclast, which breaks down bone tissue to release calcium and phosphate minerals into the bloodstream. These cells work together to ensure the bone's growth, maintenance, and repair.

How does the vascularization of bone tissue contribute to its function?

Bone tissue is highly vascularized, meaning it has an extensive network of blood vessels. This vascularization is crucial for several reasons. Firstly, it allows for the rapid delivery of nutrients and oxygen to bone cells, which is essential for their survival and function. Secondly, it enables the efficient removal of waste products. Importantly, the high vascularization also facilitates quick and complete healing of bone tissue after injury, as blood vessels can deliver the necessary cells and nutrients for repair. This vascular network travels through central canals within the bone, ensuring that even the innermost cells receive adequate blood supply.

What is the role of collagen fibers in bone tissue?

Collagen fibers play a crucial role in bone tissue by providing it with strength and flexibility. These fibers are part of the organic component of the bone's extracellular matrix. Collagen's tensile strength helps bones resist stretching and twisting forces, while its flexibility allows bones to absorb impact without breaking easily. This combination of properties ensures that bones are both strong and resilient, capable of supporting the body's weight and withstanding various physical stresses.