The first part today's lecture discusses histological sections regarding ossification.

Before starting with the slides:

-When spongy bone is seen in a sample taken from an embryo without any bone marrow in

between, the type of ossification is: Intramembranous.

-Endochondral ossification occurs in long bones.

Slide # 2

Metacarpals and phalanges are short long bones each divided into a shaft and two ends; so as

to as it is practical to examine them under the process of endochondral ossification. This slide

shows a fetal (before birth) finger. Here, the shaft is almost bony. The red colour of its matrix

is red. Moreover, the two ends are still blue in colour.

The ossification is in an advance stage; the shaft is made of bone, but the two ends are still

composed of cartilage. This picture was taken before the birth or just after birth.

Slide # 3

This is a magnified view of a part of a

phalanx or metacarpal. The end of the bone is

still cartilage, yet although hyaline cartilage is

deeply basophilic, this is not apparent in this

slide due to the old staining.

*Question:

How was this bone formed?

In the process of intramembranous

ossification. To clarify, it was formed

from a primary centre of ossification

which is the first step. Before birth in

the prenatal phase.

To be more specific, by the end of the seventh-eighth week or second month.

Bone is formed on the surface of the cartilage. This bone is called: membranous bone.

Whereas, on the surface of the calcified (dead) cartilage inside, bone is formed. This bone is

called: endochondral bone.

The blue/red appearance inside is merely the calcified cartilage/calcified bone complex. This

gets resorbed leaving a cavity in which bone marrow is starts to appear.

Bottom line: the membranous bone remains despite the fact that the whole process is termed:

endochondral ossification.

**The periosteal bone collar was formed from a primary centre of ossification in an early

phase of the embryo's life.

The bone on the outside will remain, increase in width (thickness) and in length. By this it

forms the future shaft. All newly formed bone is spongy, it may stay spongy or convert to

**Periosteal Bone Collar

(Red).

Re

Re

*Spongy Bone, which is

irregular.

***Hyaline Cartilage;

future epiphysis.

****Epiphyseal Plate.

compact bone. Of course in the case of the shaft of the femur for example, spongy bones is

converted to compact bone to endure the heavy weight of one's body.

***At the end of the bone, there is hyaline cartilage. After birth, at a variable time which can

either be one, ten, or even thirteen years of age, secondary centre or centres of ossification

will appear. Any part of a bone which is formed from a secondary centre is called: epiphysis.

It is recognisable that here, most of the bone inside was removed and bone marrow appeared

instead.

****Epiphyseal plate (Growth plate): having an epiphyseal side and a diaphyseal one also.

Recall the five zones of this plate. The doctor mentioned them without pointing out where

each one is specifically located.

Slide # 4

A longitudinal section of an embryo's metacarpal. The irregular trabeculae have started to

convert to compact bone, this is true because

the spaces between trabeculae have become smaller.

*is formed by intramembranous ossification.

It is the spongy bone which will remain and form

compact bone.

**Bone marrow; closely packed cells. This is an

advanced stage (just before birth); because most

of the unnecessary endochondral bone is resorbed.

Slide # 5

The last zone of the epiphyseal plate is very apparent. This zone is: the zone of ossification.

Slide # 6

The zones of the epiphyseal plate.

-RZ: Resting zone; chondrocytes within lacunae.

Why not blue in this slide?

Because of a stain defect.

-The proliferating zone compensates for ossification. Notice the many rows of cells.

-HZ/MZ: The arrow in the figure indicates the direction of cell maturation, as the lacunae

enlarge.

-At the start of a blue colouring, one knows that calcification has occurred. The ossification

zone isn't shown here, but as we know we can recognise it by the blue/red complex.

Bone Marrow**

Periosteum

*Periosteal bone

collar.

Slide # 7

The same as the above.

Slide # 8

Red: Calcified matrix of

bone.

Blue: Calcified matrix

of cartilage.

Both will be removed by osteoclasts leaving a cavity in which bone marrow is produced.

-How was the red part (above the cartilage) formed?

Blood vessels enter from the outside carrying with them osteoprogenitor cells. These cells

differentiate into osteoblasts which in turn deposit bone matrix on the "falling walls" the

calcified matrix of cartilage.

-Why is bone formed inside then resorbed?

To create a temporary solid support structure. Because cartilage in the beginning is weak;

having cavities inside. The periosteal collar reinforces it, and the bone inside also does. When

the periostael collar becomes thick and strong, the bone inside is spared.

RZ

PZ MZ

HZ

CZ

Epiphysis Diaphysis

The red/blue zone is:

Zone of ossification

and not zone of

"ossification and

calcification".

Periosteal collar

-After the zone of ossification, one can see an empty space: this space is the zone of

resorption. The complex is resorbed, then a cavity is created in order to permit hemopoitic

cells to form bone marrow.

Slide # 9

This slide is very clear.

When one sees:

-Lacune enlarged: it indicates zone of maturation and hypertrophy then calcification.

-Red colour following the sequential zones: indicates zone of ossification.

Slide # 10

A magnified sample of the previous one. Here the lacunae are enlarged at the expense of the

surrounding matrix. Endochondral bone is formed by osteoblasts on the surface of the

cartilage.

Slide # 11

*Very closely packed nuclei.

**What is its destiny?

Resorption. After providing

temporary reinforcement.

One can also consider it a region

of trabeculae.

Slide # 12

Somewhere, an osteoclast with many nuclei is

present.

*Bone marrow

Calcified bone**

Calcified matrix of

cartilage.

Slide # 13

Osteoblasts and osteoclasts always accompany each other.

If we see an osteoblast an osteoclast should exist

somewhere near.

Osteoblasts add bone, while osteoclasts resorb bone at the

same rate. If only resorption is needed; when the periosteal

collar is thickened or extended ,

the osteoclasts function mainly to clear the inside in order

to make room for the new bone marrow.

Slide # 14

-One can see the osteoclasts pointed at.

-Why are the osteoclasts far from the trabeculae instead of being inside a Howship's lacuni?

Because they've dried and shrunk during the preparation of this slide.

-Just before birth, osteoclasts are very active, because they resorb all the endochondrol bone

inside so the bone is prepared to produce bone marrow. During the first months of pregnancy,

the embro's red and white blood cells are produced by the liver and spleen then gradually they

are replaced by bone marrow. So before birth, bone marrow is prepared to produce blood cells

by making room for it inside the bone as a function of the osteoclasts.

Slide # 15

It is very easy to take notice of the following:

-Inside lacunae in the trabeculum (which is inside the long bone): osteocytes.

-On the surface of the trabeculeum: osteoblasts.

But always keep in mind there may be an osteoclast somewhere nearby.

Slide # 16

Osteoclast, even if it's far

from the surface of the

bone.

Osteoblast; on the

surface of the bone.

Slide # 17

One can see remnants of bone and the bone marrow filling the created cavities. The phase of

resorption comes after ossification.

Slide # 18

Slide # 19

One can see a trabeculum, osteocytes inside it. Osteoblasts or osteoclasts outside this

trabeculum.

Question:

An osteoclast cell:

-Was originally a monocyte…right.

-Has receptors for PTH…wrong.

-Has receptors for osteoclast stimulating factor and calctonin...right.

Question:

Trabeculum inside the

bone.

Osteocyte

Calcified matrix of

cartilage.

Osteoblast or osteoclast, but usually

osteoclasts are recognized from their

multiple nuclei.

*Osteoclast.

True or False: Osteocytes at one time participate in bone resorption?

True. When chronic hypocalcaemia occurs, osteocytes and osteablasts both resorb bone.

Slide # 20

1.

*Remains.

**Is resorbed and vanished.

2.

*Is formed by subperiosteal deposition of bone. Also, bear in mind that this region is

subjected to deposition and resorption during growth. So it can get resorbed. That is of course

when bone growth in width takes place; deposition of bone from the outside and resorption of

bone from the inside. The resorbed bone leaves a cavity bone marrow fills.

-What is responsible for growth in length?

The epiphyseal plate is, but real growth is from the primary centre of ossification. From the

middle of the cartilage, bone grows towards the edges. Although the epiphyseal plate is the

growth plate, it merely separates the epiphysis and the diaphysis from each other until the

fuse together.

Slide # 21

Here the periosteal collar has become very thick, making it the future shaft. Also, the spongy

bone is converting to compact, given that the spaces are getting smaller in the spongy bone.

Recall that when compact bone is first formed, the osteones are atypical going in all different

directions. Then do the haversion systems with concentric lamellae replace them.

*Membranous bone; Periosteal collar.

*

Periosteum

**Endochondral bone.

-Question:

True or False: *developed from primary and ** developed from a secondary centre?

False.

Both developed from primary centres; both these pointed structures are part of the diaphysis

not the epiphysis.

Slide # 22

Here most of the endochondral bone is

gone.

Slide # 23

Notice that this is a sample of a spongy bone. It is clear that inside the trabeculae there are

osteocytes. It is also clear that this isn't compact bone because there a no haversian systems.

Remember its components from collagen type 1 and proteglycans.

-Intramembranous ossification:

Notice that there small amounts of bone marrow between the trabeculae, in addition to the

fact the whole sample is only spongy bone. This means this sample was taken from an

embryo and was formed by intramembranous ossification. Because intramembranous

ossification at first forms spongy bone with large cavities between their trabeculae which

aren't full of bone marrow. Also, if primitive connective tissue was to be seen in the same

sample and bone marrow wasn't present, it would indicate that it was taken from an embryo.

On the other hand, if a sample of the upper end of the femur was taken from an adult, the

cavities between the trabeculae will be full of bone marrow.

**Endochondral bone.

*membranous bone.

Slide # 24

-The shaft region is all red; meaning that the primary centre of ossification is active. Primary

ossification center ------> Bone inside and bone outside.

-But in the edge of the bone, a space is seen. These spaces signify a secondary centre. Here

blood vessels are noticeable in this space, even so, that only emphasizes the fact that

ossification here first starts from a periosteal bud coming from the outside by a secondary

centre.

-No perisoteal bone collar is formed here.

Slide # 25

There are no secondary centres in the cartilage, as there are neither any vessels nor spaces.

Secondary centre.

Epiphyseal plate.

Slide # 26

When spaces are seen in cartilage, representing blood vessels. (In this sample these vessels

aren't clearly seen.) It is concluded that a secondary centre or centres will appear also.

The boundary area is the epiphyseal plate.

Slide # 27

Same as the above:

Space/spaces in the cartilage of the epiphysis Blood vessels Secondary ossification

center after birth.

Slide #28

Slide # 29

As long as there are trabeculae in the end of the bone, and an epiphyseal plate, then secondary

centre/centres appear. Recall that whenever there is/are secondary centre/centres in cartilage,

cartilage will be replaced by bone except the epiphyseal plate and the articular surface.

Shaft

Part two: X-rays.

X-ray #1

The Hip joint. This is an adult bone, because the head of the femur is attached to the neck and

the neck is attached thereby to the shaft. I couldn't find the slide from the ones uploaded, but

this is a similar image.

This shows the following:

X-ray #2

Realise the following:

-There is no lesser trochanter, no greater trochanter not even a secondary centre for each one

here.

Head of

femur

Neck of femur

Greater

trochanter

Lesser

trochanter

Shaft of

femur

Acetabulum of hip bone

similar to the glenoid

cavity.

Shaft of the

femur

Epiphyseal

plate

*

-* can't be called the head of the femur. Because it has not yet fused with the neck; there is an

epiphyseal plate separating them. Instead it's the secondary centre of ossification for the head

to form the epiphysis.

-Cartilage can never been seen in an x-ray.

-The neck of the femur was formed from a primary centre of ossification. It is an extension of

the shaft. The shaft was formed the same way. Both the shaft and neck were formed just

before birth.

X-ray # 3

The head or the greater trochanter aren't clear. But if a white "dot" is seen in the head of the

femur, it indicates the beginning of a secondary ossification centre. Yet here there are no

secondary centres for neither the greater nor the lesser trochanter.

X-ray #4

Same thing. There are no white dots in the greater or lesser trochanters. So there is no

calcification, and no secondary centres.

X-ray #5

The lower end of the femur; the knee joint.

-Here the condyles are fused with the shafts and it's very hard to determine the site of an

epiphyseal plate. As a result, it is concluded that this picture was taken from an adult.

*Meniscus cartilage fills this cavity. So this cavity is not empty, on the contrary, it is full of

this type of cartilage.

Medial condyle of

femur

Lateral condyle of

femur

Medial condyle of

tibia. Head of fibula

*Cavity of knee joint.

Hyaline cartilage

Hyaline cartilage.

X-ray #6

Structure number 1: Epiphysis at the lower end of the femur.-

-Structure number 2: Epiphysis at the upper end of the tibia.

For the millionth time, these two structures were formed from a secondary centre of

ossification.

- But: the secondary centre at the epiphysis of the femur appears just before birth not after

birth. This is an exception.

-Notice the 1 and 2 are not yet fused with a diaphysis, separated by an epiphyseal plate.

-Something that will be repeated a lot: when one sees an epiphysis not yet fused with a

diaphysis and separated by a an epiphyseal plate, it doesn't mean that the bone is fractured.

Fusion of the epiphysis and diaphysis, happens at the age of almost 20, when the plate is

resorbed. Thus, this is an appearance of a knee of a child.

- The two epiphysises will become condyles.

-The head of fibula has no epiphysis and no secondary centre here. This doesn't negate the

fact that there is a secondary centre in the lower end. The fibula is an exception. Meaning

that, although the growing end is at its upper part, a secondary centre appears first at the lower

end ossifying first. But the upper end remains the growing one, because the lower fuses first.

X-ray #7

X: Epiphysis at the lower end of femur.

Y: Epiphysis at the upper end of tibia and not at the head of the tibia. Also, the secondary

centre here appears just before birth.

-In this x-ray, one can't see a secondary centre in the upper end of the fibula. But, that doesn't

exclude the fact that there is a secondary centre at the lower end. Because the lower epiphysis

ossifies first, despite the fact that the upper end is the growing one.

-This was taken from a child before eighteen years of age.

X-ray #8

The same as above.

-What is the unseen structure?

The epiphyseal plate.

-There is no secondary centre in the head of the fibula, but if there were, that definitely means

that there is a secondary centre at the lower end.

X-ray #9

This shows an ankle of a child.

-There is an epiphysis at the lower tibia not fused with diaphysis, the same for the lower end

of the fibula.

X-ray #10

The elbow region.

1: Olecranon process.

2: Coronoid process

3: Head of radius.

X-ray #11

A side view of the previous image.

X-ray #12

* Secondary centre of ossification for the capitulum, meaning the child is two years old or

more. The first centre appears for the capitulum and the lateral half of the trochlea at two

years of age. Then for the medial epicondyle at five. For the rest of the trochlea at eight and

for the lateral epicondyle at ten.

-This centre is closer to the humerus, thus isn't for the head of the radius.

-There are no secondary centres for the head of radius, olecranon,

the lateral or medial epicondyles.

-The age of the child here is: more than two years and less than

five because the medial epicondyle isn't formed here.

-The head of radius, medial epicondyle of the humerus and the

olecranon process all exist, but they're not seen here because at

this age they are still cartilage.

X-ray #13

This shows the wrist.

-Notice the secondary centre just below the lower end of the radius.

-Notice also 3 carpal bones. If this were to be a picture of a newly born baby, NO carpal

bones will be seen. The number of carpal bones seen, indicate the pproximate year of age.

Here, the child is three years old. But just after birth tarsal (opposite of carpal) bones are seen.

X-ray #14

One can see all the carpal bones, yet at the lower ends the epiphysis and diapiphysis of each

the radius and ulna, are still not fused. One concludes, this picture is for a child.

X-ray#15

*

A secondary centre are supposed to appear in the head of metacarpal bones, whereas in

phalanges they appear in the base. The first metacarpal bone however is an exception; the

secondary centre appears in the base of it. For a long time, it was thought that there was no

metacarpal for the thumb. But that was because it was only different than the rest of the

metacarpals.

The first metacarpal can be approximated to the rest of the digits by 90 degrees; this is

necessary for opposition which is when we count our fingers. But opposition is mostly

important for determining a pincer-like grip.

Also, the first metacarpal is shorter than the others.

X-ray #16

3: Scaphoid.

4: Triquetral.

5: Hamate.

-Given that all the bones are seen, this is for a child above eight years of age.

X-ray #17

Not sure this is the right slide; as I can't seem to find the window of

the doctor's neighbor in the picture.

*One can recognise a fracture just above the lower end of the radius, but at

the lower end, there is an epiphysis and a diaphysis still not fused together.

X-ray #18

One can see an apparent fracture of the radius bone, as it is not in its right

place.

X-ray #19

Trapezoid

Lunate

Trapezium

Capitate Pisiform

*

It is very clear that this is a picture of an adult's wrist. Because the lower end of the radius is

fused with the shaft. The ulna is likewise. In addition, all the carpal bones are apparent.

--------

-Please remember to check ALL the slides, I didn't include all the images of these slides. Just

the ones that needed farther labeling and extra clarification, as there are some which are very

clear and are also well labeled.

Above the silver stream, sprinkling water, trickling thoughts…a lost dream behind a crooked scene. Near

the corners of a face, a crinkle, a tremble, a shake. Through the steaming tears, through the malicious fears;

a weary mind tries to see. A throb, a fast pace, a rush of blood. A gasp, a beating throat, a drowning flood.

At the ridges where the sea water would sway back and forth on the coasty sand. Under the starry magic,

where the glittering star dust flickers in the air, spontaneously. You swear the dancing air lines your lungs,

with glistering fragranced lace of majesty. Down in the southern hemisphere, a kangaroo would perfectly

salute you. Just behind the torn curtains, lines of gold sunlight come streaming in.

To the one who spoils Dr.Faraj's jokes or funny mockery for me. And spills them all out on me before I

hear them from himself. The one who helps me a lot in each sheet I write. To the one who burns the

darkness, and lights the way instead. To the one who makes me see the beauty in things...

To the one and only: Hanin Kayed.