Cartilage and Bone - Key Points

Image from:http://normankpoppenmd.blogspot.ie/

Here are some points I want to emphasize about cartilage and bone.

1. Cartilage is avascular. Therefore it heals poorly and the damaged cartilage is replaced by dys/non-functional scar tissue.

2. Cartilage can grow both by apposition (deposition on surface) and by interstitial growth (expansion from within)

3. In growing cartilage, the perichondrium is the source of new chondroblasts/chondrocytes

4. Both fibrocartilage and articular hyaline cartilage entirely lack perichondrium.

5. Shrinkage of the nucleus pulposus of the IV disk occurs as a normal part of aging and results in a decrease in height of the individual.

6. Bone is highly vascular. Therefore it heals well and damaged bone is (generally) replaced by new fully functional bone.

7. Bone deprived of its normal blood supply will undergo avascular necrosis and die. This has important implications in the management of certain fractures which interrupt the normal blood supply of the bone.

8. Bone deposition and growth is always appositional, never interstitial

9. The highly vascular nature of bone also facilitates its role as a reservoir or sink of important metal ions. These can be rapidly absorbed from blood, or resorbed from bone and secreted into the blood.

10. The internal cavity of bones (medulla) is where bone marrow is found. Bone marrow is the source of stem cells from which all blood cells are derived. Some bone marrow stem cells can also give rise to other tissues. The medullary microenvironment is an important regulatory factor controlling the behaviour of these stem cells.

11. The rates of resorption and bone deposition are highly regulated and interlinked. Normally about 10% of the total bone mass is undergoing remodelling at any given time. When the rates of resorption and deposition become unlinked, or the relative kinetics change, bone disease can occur. Two such (unrelated) diseases are osteoporosis and Paget's disease. In osteomalacia, a disease of defective bone mineralization, the primary cause is lack of Ca due to vitamin D deficiency (rickets).

12. In surgical procedures involving bone, every effort is made to preserve the periosteum as it is an important source of osteoprogenitor cells from which osteoblasts are derived.

Fibrocartilage

As I mentioned in the video, fibrocartilage is interesting because the appearance depends in part on where the fibrocartilage comes from. Although relatively disorganized, it is at its most organized in the annulus fibrosus of the intervertebral disc. Here, it must be particularly good at resisting compression.

The picture above and to the right is a low mag view of an IV disc from a small monkey.
AF = annulus fibrosus NP = nucleus pulposus.
The disc resembles a 'jelly doughnut' where the annulus fibrosus is the doughnut and nucleus pulposus is the jam centre. The force the disc experiences is mainly compression along the axis from top to bottom of the picture.

Microscopically, the fibres of collagen Type I are arranged in layers, with the fibres in adjacent layers oriented at right angles. Chondrocytes are generally found between the layers. This gives the classic 'herringbone' or 'chevron' appearance to the fibrocartilage.

An explanation as to why having the fibres oriented in this way is advantageous in distributing load to reduce compression is shown in the cartoon diagram below.

Elsewhere, fibrocartilage must not only resist compression, but also twisting and shearing (sternoclavicular joints, pubic symphysis). Here the fibrocartilage will appear disorganized, with bundles of fibres interwoven among one another seemingly at random.Although appearing disorganized, the fibrocartilage is organized in such a way so as to maximize strength and this is why dislocations of the pubic symphysis or sternoclavicular joints are relatively rare.

Cartilage

Here are three short clips on the subject of cartilage. The first is a brief general overview, and the next two deal with the appearance of cartilage on slides viewed with the VM.

Cartilage General Overview




Hyaline Cartilage



Elastic and Fibrocartilage

Cartilage and Bone

Image from: http://cloud.med.nyu.edu/virtualmicroscope/v/174/

By now I am assuming you have covered the cartilage and bone chapters in the notes so you should probably begin the practical elements of these also. The attached document contains the instructions you will need and there are various video clips posted here to guide you in your use of the microscope. As always if you have any questions email me.

Ground Bone

A brief explanatory video on what can be seen on one of the ground bone slides.

Bone

Here are three videos covering most aspects of bone that I would expect you to know. In two cases we are looking at developing bone, while in the third we are looking at fully (or nearly fully) developed lamellar bone. You will study decalcified lamellar bone and you should attempt to compare and contrast this with the ground bone specimen you have viewed previously. You will study the epiphyseal plate, the hyaline cartilage structure which drives growth in length of long bones and on this slide you should concentrate on recognizing and understanding the process taking place here. Finally you will look at a developing animal paw with the purpose of gaining an overview of endochondral bone development.

Decalcified bone:



Epiphyseal plate:



Endochondral bone formation:

Bone growth dynamics

Here's my cartoon version of the dynamics of bone growth at the epiphyseal plate which is the mechanism by which long bones grow in length, and an explanation of how bones grow in width. Note that growing in width requires a balance between new bone deposition and bone resorption, and that bone resorption normally occurs only on the internal (marrow cavity) surface of the diaphysis.

It's also important to be aware that in general bone deposition and resorption occur simultaneously on the inner surface of bone and these two activities are very tightly linked and regulated. Paget's disease is a condition in which these activities become unlinked and the result is dysmorphic and inappropriate bone growth in places, accompanied by bone thinning and excessive resorption in other places.


Bone dynamics:

Epithelium and Connective Tissue

Image from: http://o.quizlet.com/i/gDRxNXQjv3Xngqv4038dvw_m.jpg

The attached document contains some instructions regarding what you must cover for the practical element of epithelium and connective tissue. I am assuming that you have been reading the notes on these topics.

You can find the slides I refer to by searching for them by name or number on the NYU VM.

Have a go at completing an eNoteBook once you have viewed/reviewed the slides. Let me know how you get on. If you encounter problems email me and if there are particular problems faced by more than one or two of you I will post solutions for all to see.

Epithelium and Connective Tissue

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Getting started

Hi all.

I am in the process of finalizing the materials you will need to complete the practical assignments for the module. Before I begin to post all of these, I want to make sure that everyone is ready and able to use them.

I have provided two templates for you to use to make your notebook entries. One is for PowerPoint users, the other for Keynote users. If you cant use either of these let me know and I will see what Ican do to assist.

From the BlackBoard site download the template of your choice. Open it, then immediately save it to your local drive using a sensible name.

Now navigate to one of the virtual microscopes we will use. You will find it at
NYU Virtual Microscope.

Bookmark the site as you will use it a lot. From the menu on the top choose 'Collections' then choose 'Histology Slide Collection'. Find a slide that interests you and click on it. Familiarise yourself with changing magnification and navigating around the slide. Repeat this for a few more slides until you are comfortable with using the virtual microscope.

Of course none of this is of any use unless you can actually take a picture of what it is you are looking at on the virtual microscope to include in your notebook. How you do this depends on what type of computer or device you are working on. On a MAC OS X 10.X.X the easiest way is to hit CMD and SHIFT and 4 simultaneously. The mouse pointer becomes a cross-hairs. Click and Drag this over the part of the screen you wish to capture. Release the mouse button and a screen shot of the area you specified appears on your desktop.

If you use Windows you can use the snipping tool. How you access this depends on which version of Windows you are using.

Windows XP / Vista: http://news.cnet.com/8301-13880_3-10040133-68.html

Windows 7: http://windows.microsoft.com/en-IE/windows7/Use-Snipping-Tool-to-capture-screen-shots

Windows 8: http://www.thewindowsclub.com/snipping-tool-capture-screenshots-windows-8-tips

If you are using the PowerPoint template, use can use the screen clipping tool available from the insert image tab on the ribbon.

Regardless of what computer you use, it is a good idea to make one folder in which you will collect all of your histology images (you can organize these in subfolders by topic or slide if you wish). Now using the copy of the notebook you saved earlier you can practice inserting pictures and typing text associated with the picture (what you write is not important for now). It is worth practicing to use the drawing and labelling tools to mark up images.

If you have any problems with any of the above email me

Introduction

Here are some video descriptions you may find useful if you are learning histology. I have structured the blog so that as you scroll down, you will encounter video descriptions in approximately the order you should learn the histology of the fundamental tissues.

Most of the clips are descriptions of slides that can be found at the publicly accessible NYU Virtual Microscope . If the slide described is not from the NYU VM then it is an equivalent slide, and using a similarly named slide from the NYU VM you should be able to see the same basic features.

These videos were originally prepared as part of a distance learning course in histology, and the depth and scope of the material may not be appropriate to your studies. In case of any doubt please check with your histology professor/lecturer/tutor if these descriptions are appropriate to your specific course.

If you have any questions or comments please post them in the comments section beneath the appropriate video, or directly in comments on the You Tube channel.

BW

Virtual Microscopy

Here's a short videoclip on two of the virtual microscopes (VMs) I recommend (there are others). For this year we will emphasize using the NYU VM, but you are free to use any other you wish. The purpose of this is just to introduce you to the basic interface and function. Both are very simple and require little if any learning.

When you are trying out the VMs, don't panic if at first  everything looks just like a jumble of blue and pink. I'll post short instructional video sequences and sketches to help you find what you must see and record.

BW.

Intro to Practical Histology

Here's a brief introduction to practical histology.

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After watching the video clip you may wish to explore this slide yourself. You can do so by clicking on the image below.

Click on the image to explore the slide

Completing epithelia and connective tissue

These last two clips complete your guidance on epithelia and connective tissue. They cover urothelium and two specialized types of connective tissue fibres, elastic fibres/lamellae and reticular fibres.

Urothelium



Elastic fibres and reticular fibres

More on Epithelia and Connective Tissue

Continuing our investigation of various epithelia and connective tissues, here are some more short video clips describing some of what can be seen on a few of the slides I have recommended you look at. Remember, you are not limited to looking at the specific slides I recommend and indeed I encourage you to look at other slides and to use the U of I VM also.

Simple columnar, loose connective tissue



Simple cuboidal and squamous



Loose and dense connective tissue, adipose tissue




Classic loose connective tissue of the mesentery.

Epithelium - practical histology

Exploring aspects of the appearance of some epithelia.



BW

Epithelia - Some Key Points

You should note the following key points.

NYU Virtual Microscope 117.68

1. Epithelia are sheets of cells that line external and internal body surfaces.
2. Epithelia present a barrier to the free movement of substances from the external environment (external world, or lumen of hollow organs) to the internal environment.
3. Epithelia operate specific transport mechanisms for some substances such that they are selectively transported either from the external to internal environments or vice versa
4. All epithelia are attached to a 'carpet' of glycoproteins, proteins, glycosaminoglycans and proteoglycans called the basement membrane.
5. In addition to acting as an attachment platform, the basement membrane also
(a) regulates the behaviour and structure of the cells attached to it
(b) prevents the migration of epithelial cells into the interstitium
(c) acts as an ultrafiltration device regulating what molecules can cross into and out of the epithelial compartment
(d) is the structural interface between the epithelial sheet and the underlying connective tissue.
6. All the cells in an epithelium are attached to one another by intercellular junctions, and the number and type of these junctions determine the structural stability and permeability of the epithelial sheet as a whole.
7. All epithelial cells are linked to one another by gap junctions, non-structural junctions which permit the free diffusion of small molecules between all of the cells in an epithelial sheet. This means all the cells in an epithelium are metabolically coupled to one another.
8. All epithelia undergo turnover at characteristic rates. This implies all epithelia have a reserve stem cell population from which new epithelial cells are derived by mitosis, and that the rate of cell division is tightly coupled to the rate of cell loss.

From a traditional histology perspective the following points should be noted:

9. The basement membrane is not always visible without special staining techniques.
10. Epithelia are classified as either;
(a) simple, a single layer of cells all of which are attached to the basement membrane or
(b) stratified, two or more layers of cells in which only the innermost layer of cells is attached to the basement membrane.
Pseudostratified is an additional classification in which there is a single layer of cells all attached to the basement membrane, but the cells are different sizes and shapes and so gives rise ot the appearacne of being stratified.
11. In addition to the above classification, epithelia are also classified according to the shape of the OUTERMOST cell layers (the inner cell layers are most frequently round or polygonal). The possible shapes are
(a) cuboidal - cells approx. same height and width, generally round nucleus occupying the centre of the cell
(b) columnar - cells are taller than they are broad, generally oval nuclei, which may be displaced toward the bottom or top of the cell
(c) squamous - cells are flat and paving stone like, generally flattened oval nuclei which may cause the apical cell surface to bulge outward
12. If the cells in the epithelium display certain specializations (e.g. cilia) there are also noted (i.e simple cuboidal ciliated epithelium)
13. Epithelia often do not look exactly like their classification because of the method of tissue preparation or the angle at which the tissue was sectioned. Recognizing specific epithelia is a skill that comes with practice. You are generally not expected to identify unknown epithelia, so you will learn to match the actual appearance of a given epithelium with the appearance it should have.

Finally, on the basis of the above, what kind of epithelium is shown in the image accompanying this post?

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The blog is now also formatted for viewing on a mobile device such as your phone. This is a new experimental feature so if you use it let me know how it works out. So far it seems pretty good on my phone!