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MCAT
Course: MCAT > Unit 7
Lesson 16: Skeletal systemMicroscopic structure of bone - the Haversian system
In this video we will explore the microscopic structure of bone or the Harvesian system in depth. Created by Tracy Kim Kovach.
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what is the trabeculae of a spongy bone made of?(4 votes)
Bone. Bone is composed of a calcium, phosphorus mixture called hydroxyapatite layered over protein than gives bone some flexibility and much support. Spongy bone looks weak but it is actually strong and responding to the torque and stress on the bone as we grow and move. Spongy is a poor description for something that is forming the 'flying buttresses' of our bones. https://en.m.wikipedia.org/wiki/Cancellous_bone
https://depts.washington.edu/bonebio/ASBMRed/structure.html(6 votes)
Can someone please explain what are lacunae and canaliculi ?(1 vote)- The osteocyte, when immature, is called an osteoblast. This cell produces the boney matrix, releasing it outside of the cell. As a result of it's work, as well that of other osteocytes, they form the boney caves or spaces in which they reside, called lacunae. The lacunae are connected by caniculi, or little canals. Inside the caniculi, extensions or arms of the osteocytes travel to touch the osteocyte next to them, above them, and below them So they can exchange materials even though they are encased in lacunaes. Long ago, when people first looked at bone they did not have all the equipment we have today and they named things based on what it looked like to them. They thought the small spaces must be filled with fluid, so they called them lacunae or little lakes. These lacunae are connected by many tunnels, so these were called caniculi, or little canals. We now know this is incorrect, but the names have remained. They are a poetic reminder of where we came from, and how something so preposterous as having live active cells interacting in a material that appears so inanimate might actually be true. Excellent stuff bones! Rock on osteoblasts.(7 votes)
Hi ,
At1:32, it is said that the spongy bone is there to make the bone lighter.
I would have made the bone empty to make it even more lighter.
So, I guess this is not the only reason of the existence of spongy bone ?
thanks for the response(0 votes)
Spongy bone is important for a number of reasons. Firstly it is weaker but more flexible than cortical (compact) bone which it is very hard and strong but ridged (generally things that are ridged and hard do well under compression but not tension/flexure), so areas that come under flexure (eg ribs, ends of long bones) may benefit. Also it has a larger surface area than compact bone and therefore can exchange ions such as calcium easily, which is important in bone metabolism (freeing calcium vs storing). Finally as you say having hollow bones would be lighter than having spongey bone however there needs to be a compromise to provide enough structural integrity without being too heavy, which combining a spongy flexible interior and hard tough exterior provides (think of a knights armour chain mail covered in steel plate armour). Hope that helps(10 votes)
- What is periosteum made of?(2 votes)
It's made up of CaCo3, osteocalcin, osteopalpin,
The periosteum is the hardest tissue in the body
the hardest material is enamel that form the covering of the teeth(2 votes)
Whats are the differences between microscopic appearance, location, and function between spongy and compact bone?(2 votes)
Spongy bone is the inner framework of the bone in which the bone marrow resides. Hematopoiesis takes place here or fat cells might be stored depending on the location. Microscopically compact bone has the features elucidated in the video (osteons), while the spongy bone is less dense and shows a framework of trabeculae.(2 votes)
what are cartilage bones and dermal bones?(3 votes)
Cartilage
Cartilage is not a type of bone but is rather a type of connective tissue (like tendons are).
From flexible to rigid:
Elastic cartilage = ex. ear, larynx, epiglottis
Hyaline cartilage = ex. between joints, nose
Fibrocartilage = ex. between bones and ligaments (bone to bone), between bones and tendons (muscle to bone)
As you can see, it is used in places where bone would be too rigid of a structure for human needs. It is also the precursor to bones in endochondral ossification: as the body develops certain cartilage areas become bone.
Dermal bones
There are 2 ways in which ossification occurs (creation of bones).
Dermal (also called membrane) bones are formed through intramembranous ossification: creation of bone in layers. Ex. Flat bone ossification.
Endochondral bones are formed through endochondral ossification: creation of bone with a cartilage precursor. Ex. Long bone ossification.(1 vote)
Is this true for all bones?(2 votes)- for anything that classifies as a “bone”, yes.
notice that some parts of the body that are "hard" are not necessarily “bone”. such as teeth, they are not classified as "bone" because they are made of Enamel and Dentin rather than how bones are made of calcium phosphate and Collagen. Also, there are different types of bones with other different structures (Flat Bones, Long Bones, Short Bones, Irregular Bones), though this video describes a structure true for all(1 vote)
3:05. Are the gap junctions in the Haversian canal? The video says that canaliculi connect the lacunae to the Haversian canal to allow osteocytes to communicate, but the osteocytes are all in the lacunae, right? So why go via the Haversian canal?(2 votes)- No, gap junctions are in between the canaliculi and osteocytes which are in the lacunae.
Osteocytes are the cells and they use canaliculi to communicate with each other. Gap junctions are systems that connect the cytoplasms of cells so they could communicate (in this case it goes: Osteocytes -> gap junction -> canaliculi -> other Osteocytes gap junction -> other Osteocytes).
Osteocytes do not need to connect to the Haversian canal to communicate with each other. It is just that the canaliculi “stem” from the Haversian canal. They are really just a web that connect all the osteocytes in the lacunae.(1 vote)
can you actually explain the term osteon?(2 votes)- osteon is the functional unit of mature compact bone (aka Haversian system)(1 vote)
describe microscopic features ofosseous tissue to help longbones without breaking(1 vote)- How are the Volkmann related to the Harversian canals(2 votes)
1:32
Video transcript
- [Instructor] All right so
we're going to be talking about the microscopic structure of bone and in particular, we're
going to be talking about what is called the haversian system. Now let's take a piece of
bone and cut it in half and see what it looks like on the inside. Here, we basically have a cross
section of a piece of bone. So let's take a look inside. Now the inner most portion of this bone is made up of, what is
called, spongy bone, which is otherwise known as
cancellous or trabecular bone. And here you can see
this arrow pointing to the trabecula of spongy bone. So it's no surprise
that if you take a look at spongy bone, that it looks pretty much a lot like a sponge and
in fact, because of all these various trabeculae or cavities, the surface area of
spongy bone is 10 times that of the outer layer of compact bone. So basically spongy bone
is just this porous network of spikes surrounding
the innermost portion of bone marrow. And the overall effect
of this spongy network in the center of the bone is that of making the bone lighter. Now if you look at the
periphery of the bone, you have what is the harder, denser layer that surrounds the spongy bone. That is called compact bone. Compact bone, it's no
surprise, that it's, well, more compact than spongy bone. It has fewer gaps and spaces, but what really makes
compact bone different from spongy bone, is that
it has a specific type of organization made up of these osteons, these repeating functional units. Here's a blown up view of an osteon. Another word for these osteons
is the haversian system. So let's talk more about
this haversian system. So each of these osteons
looks like of like a cylinder and it has multiple
concentric layers of bone, or sheets really, that
wrap around each other to form this osteon. Each of these layers is called a lamellae. In the center of these layers is a canal called the haversian
canal, or central canal. In this canal travels blood
vessels, lymph vessels and nerves as well. Now in between these sheets
of lamellae are these tiny channels that are called canaliculi, which you can kind of see here. They branch out from the
central haversian canal to these empty spaces
that are called lacunae. Whenever you see the
word lacuna or lacunae, you should think empty space. So each of these lacunae is
really just an empty space or osteocytes or bone cells. These osteocytes have these
long cellular processes that branch through the canaliculi to contact other osteocytes
via gap junctions which allow these cells to
communicate with each other and exchange nutrients and
signals with each other. Finally, you have these volkmann canals which are canals that run perpendicular to the haversian canals. And these connect osteons to one another and also, as you can
see, carry their own set of small blood vessels. Let's not forget that the
very outer most superficial layer of bone is called the periosteum. Peri meaning around or surrounding and so that's the layer of
bone that is on the outermost that you can actually
see with the naked eye.