(13) salivary glands and tmj

8/2/2019 (13) Salivary Glands and TMJ

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Continue with salivary glands

Last time we stopped at stroma, and we said thatanything related to the physiology of secretion or function

of saliva will be included in the oral physiology. So the

slide which is about synthesis of saliva (slide 10) is not

included here; as well as next slide (secretion of saliva).

As we said, we have three types of salivary glands;

serous, mucus, and mixed, and we said when we have a

mixed acinus, we should have a core of mucus glandcapped with serous demilunes.

Regarding the serous cells,

under light microscope, its

basophilic (stains dark) and this

is because it contains rough

endoplasmic reticulum and its

very active in protein synthesis.

Characteristic granular

appearance, because it has

many granules filled with

proteins; these proteins are to

be secreted into saliva, and it has round prominent

nucleus located at the basal third of the cell. When you

see the Ultra-structure, it has Wedge-shaped outline as

its wide at the base and narrow at the apex.

Luminal part contains zymogen granules, these granules

are to be secreted into saliva and it has many microvilli to

increase the surface area of secretion. Desmosomes, gap,

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and tight junctions between these cells and adhesion cells

within the acinus itself. Of course, these cells have a

basal lamina that separates it from the surrounding

stroma.

Moving to the Mucus cells, its

different than serous. First of

all, it stains light (pale) under

Hematoxylin and eosin

staining, why?? Because it

contains too many

carbohydrates. The nucleus is

located basally but its

compressed, not rounded as in

serous cells. As we said, the acini may be surrounded by

crescent-shaped serous demilunes; some researchers say

that the demilunes that capes the mucus cells are directly

attached to the lumen itself and others say its not;

because the secretion have to pass within the mucus cells

to reach the lumen.

Myoepithelial cells: they are cells that squeeze thecontinents of the acinus; it lies between the basal lamina

and the basal membranes of the acinar cells and the

intercalated duct (ICD). Its located around the acinar

cells; its dendritic (has many dendrites) and has long

tapering processes. Myoepithelial cell also surrounds the

first part of the duct, which is the ICD. In this way, itslongitudinal and it has few short processes. So, the shape

of the cell becomes different if its surrounding an acinus

or ICD. The contraction of the cell is controlled by the

parasympathetic and the sympathetic activity. In ultra-

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structure, the cell has a flattened nucleus, desmosomes

with parenchymal cells, and Gap junctions and

hemidesmosomes with basal lamina.

Regarding the intercalated duct, which is the first partof the ductal system, it drains from several acini, and its

compressed between these acini; thats why its difficult

to find the ICD in histology. The lining cells are cuboidal

simple epithelial cells with prominent nuclei. ICDs are

long, narrow, and branching in parotid gland.Thats

why best site for viewing ICDs is in parotid section. Many

ICDs open together to one striated duct.

Striated duct is longer and larger than ICD and its

composed of simple columnar epithelium with large

centrally- located nuclei. Luminal surfaces have microvilli

to increase the secretion and absorption surfaces and the

basal surfaces are separated from connective tissue by

basal lamina. It has a striation (thats why its called

striated duct) and these striations are corresponding to

multiple infoldings of the basal membrane of the cells.The cells are connected together by means of

desmosomes. Electrolyte reabsorption and secretion are

allowed. In other words, we have active reabsorption and

secretion of molecules and minerals in the stage of

striated duct. We have secretion of epidermal GF and

Kallikrein (these were discussed in details in oral

physiology)

Now the collecting duct is the duct that drains from

many striated ducts. They are bi-layered epithelium; the

surface layer is columnar and the basal one is cuboidal,

and it lacks striation. As it enlarges, it gets a connective

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tissue adventitia and its terminated as stratified

epithelium, why?? Because they have to merge with the

oral mucosa. You must remember that the collecting duct

is always surrounded by a connective tissue, so, if you

find a duct thats not surrounded with C.T, you should

know that its not a collecting duct, because they are

located between the lobules, not with the lobules like ICD

and striated duct.

The parotid gland is the largest gland and its only

composed of serous acini, so, it has only watery secretion.

Parotid glands differ between adults and infants. In

infants, the volume of the parenchyma is too little

because its still developing, so, we have too many

connective tissues. In the other hand, theres a big

volume of parenchyma in adults parotid gland and

theres also many fat cells, and they become more and

more as we advance in age.

The submandibular gland is the second largest gland

and its mixed gland but the number of serouscomponents is more than the number of mucus ones with

ratio of 7\3. So, the secretion in this gland is not 100%

watery but its semi-watery. The intercalated ducts are

short and difficult to locate in this gland, while the

striated ducts are long and very obvious.

Regarding the sublingual gland, we have 2 segments

that all empty to the sublingual fold. This gland is a majorsalivary gland, but actually its composed of a number of

minor glands (8 to 30) collecting together to form this

major gland. Its also mixed gland but here the mucus

cells are more than the serous ones, and theres NO

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serous cells located independently; they must be as a cap

for the mucus acini. Sublingual gland also lacks striation.

Minor salivary glands are distributed within the

mouth (we have Labial, buccal, palatal, palatoglossal, andlingual minor salivary glands) and most of them are

mucus except the Von Ebners gland. If we take the

Lingual gland we can find three types; anterior, posterior,

and von ebner glands.

1- Anterior gland: are mixed glands (not mucus as in the slide)

that are embedded in muscle near the ventral surface of the

tongue.

2- Posterior gland: are mucus glands that are located at the root of

the tongue.

3- Von ebner gland: are serous and associated with thecircumvallate papillae.

Clinical consideration:

Xerostomia: is a problem in secretion of saliva and it

causes the mouth to dry. Because saliva has a role in

protection the mouth, we also expect to see injuries on

the mucus membrane, because saliva is important in

buffering the minerals, we see caries, because saliva is

important for the health of periodontal ligament, we see

periodontitis, and because saliva is important in digestion

of starch, we can see Dyspepsia (difficult digestion), and

so on. These are caused by many things such as:-

1- Drugs.

2- Loss or destruction of salivary tissueby radiotherapy, autoimmune

disease, or salivary gland surgery.

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3- Endocrine disorder caused by diabetes or hyperthyroidism.

Well not take next slides because we are going to take

them next year. So, by this we are done with the first partof this lecture and now well start a very interesting topic

which is the TMJ and the joints of the

craniofacial complex.

TMJ and the joints of the craniofacial complex

The function of the joints within the head and neck are

mobility and growth. The TMJis important for the mobility

since it allows for the depression, elevation, and lateral

movement of the mandible and its also important in the

growth of the ramus because it contains cartilage thats

growing. Joints of the trunkand the joints of the upper

and lower limbs also have a function of mobility. And we

have joints that are associated with growth, such as the

craniofacial joints, which include other joints and we are

going to talk about them later.

So, mobility: TMJ, Joints of the trunk, and joints of

the upper and lower limbs.

Growth: TMJ and craniofacial joints

Craniofacial joints: it includes:-

1- TMJ.

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2- Synchondroses: which are located at the base of the skull.

3- Symphysis menti: which is the junction between the two halves

of the mandible.

4- Sutures: which are the joints between the flat bones of the cranial

vault, and its separated to simple and serrated sutures.Bone Formation:

We have two types of bone formation; endochondral

ossification and intramembranous ossification. When we

have the mesenchymal tissue converted into cartilage

and take the 3-D structure of the bone, this is called

endochondral ossification because this will be

replaced later on by bone, but when we dont have anyinvolvement with cartilage, and the mesenchymal tissue

is converted directly into bone we call it

intramembranous ossification.

We find endochondral ossification at many sites:-

1- The base of the skull.

2- At the nasal septum and nasal capsule: which will become the

ethmoidal bone. Why ethmoidal bone has to be endochondral?Because its complex.

3- Coronoid process.

4- Condylar process.

5- Ramus of the mandible.

But we find intramembranous ossification at:-

1- Cranial vault.

2- Facial skeleton including the maxilla.

3- Body of the mandible.We have a cartilage thats important in the formation of

the body of the mandible but its not replaced by bone (it

disappear finally) this is the Meckels cartilage.

Epiphyseal growth:

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This is what happens in long bone formation. If you take

your tibia, as a long bone, what happens in the formation

in it?? It starts simply by mesenchymal tissue, then, this

mesenchymal tissue starts to have collar of bones at the

periphery, then, blood vessel penetrate to provide

nutrients in the central part. But finally, well still have

cartilaginous tissue, and this tissue will be responsible for

the elongation of the bone. Now, some people who have a

problem in growth hormones, so they have a problem in

the Epiphyseal plate, theyll have a normal trunk and

head but very short limbs, this

condition is called chondroplasia.The Epiphyseal plate remains active

until the age of 18-20 years.

The cell that is responsible for the

growth of this plate will do so by

many stages or zones:-

1- Resting zone: the cells have no

activity at the zone.2- Proliferative zone: the cells start to

proliferate. And they become chondrocytes, which are the cells

that deposit the cartilage, and these divided to form parallelcolumns; then, they get enlarged and enlarged until they reach the

next zone.

3- Hypertrophic cartilage zone: in this zone, the chondrocytes are

large now and they have the cytoplasm filled with glycogen, then,

this cartilage starts to calcify.

4- Ossification zone: ones the cartilage is calcified, bone come andreplaces this cartilage.

Its important in endochondral ossification to remember

that cartilage DOES NOT change to bone, thats wrong.

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The right thing is that the cartilage goes under

calcification then the bone come and REPLACES it.

TMJ:-

the function of TMJ and the reasons that its a specialjoint, we took them in oral physiology ( I love this word

:D ).

And u took the soft and hard tissue component in

anatomy ( Anatomy !!! thats new )

Anyway, this joint is unique because it has a disc, which

separates the joint into an upper joint and a lower jointcavity, and the joint is capsulated by a capsule. We also

have some ligaments in this joint; sphenomandibular,

stylomandibular, and tempromandibular lateral ligament.

TMJ is a synovial joint, which has a synovial membrane

which in turn secrete a synovial fluid thats important for

the lubrication. ( am not gonna ask you about the

histology of the TMJ because for sure you have taken it inbasic histology, DID WE !!! ^o* )

Now, lets skip these slides (we are going to go back to

them later),

*-* the doctor was describing the picture of the

TMJ of the child, but sorry I didnt get what he is

pointing at; anyway, here what he said *-* (and

lets see the TMJ of the child. We have the intra-articular

disc, the condyle, the glenoid bone, upper and lower joint

cavity, and the articular surface that cover the joint,

which is fibro cartilage ( not hyaline cartilage), after that

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you can see the fibrous articular surface, then, well find

the proliferative zone, then, we see a very thick cartilage,

the hypotrophic zone, the calcified cartilage zone, and

finally the ossification zone).

Back to the adult TMJ. It has different layers;

1- Fibrous articular surface zone: which is similar of the childs

TMJ, and its mainly collagenous although elastin is also present.

In upper most layer, fibrous are parallel to the surface, but in

deeper layers, they run more vertically. Articular surface

covering the glenoid fossa and eminence is similar; athough its

thinner.

2- Cellular-rich zone: which is the proliferative zone.

3- Fibrocartilaginous zone: which is fibrous layer and its remnants

cartilage-like cells.

4- Zone of calcified cartilage: which is remnants of secondary

condylar cartilage, and they have different staining from that of

bone, and finally we have the bone of the condyle.

Intra-articular disc:-

This disc is dense collagenous fibrous tissue, and we have

fibers running in different orrientations:-

1- antero-posteriorly in the central region.

2- transverse and superoinferior fibers may occur.

3- circumferentially fibers at the periphery.

These fibers are crimped or wavy, they are not running in

strait lines. In this disc, we have type I collagen (mainly)

and sometimes we can find type II and type III. Cells are

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more at birth, so, as you advance in age, cells are

reduced. The pulp of the disc is avascular, and because of

that, it derives nutrition from the synovial fluids. Actually,

we have blood vessels but they are only present at the

periphery. The superior lamella of the bilaminar zone has

numerous blood vascular spaces which are filled with

blood upon forward migration of condyle in jaw opening.

So, when we open the jaw, the disc travels anteriorly with

the head of the condyle.

What happens to the posterior part of the disc ??

All the spaces become filled with blood, and when thedisc is reduced again to its normal position after the

closure of the mandible, the area which was filled of blood

will return normal. Thats all about TMJ; now, lets discuss

what we mean by the Synchondroses.

Synchondroses:- its very important and you

got to understand it well.

They are remnants of the primary chondocranial

cartilages after endo-chondral ossification of cranial base

bones. The base of the skull is formed with endochondral

ossification, this mean mesenchymal tissue becomes

cartilage, and then the cartilage will be replaced by bone.

But the replacement of cartilage by bone is occures in all

the areas except the central area; in this central area we

still see cartilage. Thats what we call synchondroses.Again, what remains from the cartilage in the

endochondral ossification process is called

synchondroses.

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What is the function of it ? its just growth, it doesnt have a

function in mobility.

When we see the base of the skull of a baboon, *-* seems

to ba a monkey !! *-* we can see a space between thebasilar part of the occipital bone and the body of the

sphenoid, this is called the spheno-occipital

synchondroses, and this space is filled with cartilage. If

we examined a skull of an adult, we wont see this

synchondroses. but if you take a person whos only 13

years old, youll find the spheno-occipital synchondroses.

There are three areas of synchondroses within the skull,and they are:-

1- Spheno-occipital synchondroses: which we talked about and its

the most important one, because it continues growing untill early

teens.

2- Spheno-ethmoidal synchondroses: between the spheniod and

ethmoid, this will be replaced by fibrous tissue shortly after birth.

3- Midsphenoidal synchondroses: which is active prenataly and

obliterated to form the body of the sphenoid at birth and its

located between two parts of the sphenoid.

Histology of synchondroses: we have severalzones:-

1- Resting zone at the center.

2- Zone of proliferation at both sides. In the other

hand, in epiphyseal plate, we see only one sided

proliferation.

3- Zone of hypertrophy.

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4- Replacement zone: replacement by bone.

5-Zone of calcified cartilage.

6-Zone of ossification.

So, they are the same zones thats found in the

epiphyseal plate but here its in both sides. Its nice to see

here that the cells are also occuring in parallel columns as

in epiphyseal plates.

THE END

Plz Forgive me for any mistake, cuz I tried to write it as

soon as possible, cuz tomorrow is the micro exam

It was really a nice semester with the best batch in this

UNI, and I hope we r all gonna finish together to the

end :D

Thnx for every person in this batch and specially those

who are doing there best to help without naming :P :P

Now take this: *-*BAMTOBAM*-*

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Resting

zone

Proliferative

zone

Calcification

zone

Ossification

zone


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* F N Doubt- leave it out *

DONE BY: BADER ALI

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(13) salivary glands and tmj

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