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3

Leen Al-Hunaiti

Dana Al-Toum

…

Dr.Firas Al-Suleihat

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-this lecture is an introduction to the digestive system. (Oral cavity is the first part

of the digestive system).

*Tongue and Salivary Glands:

⁂Tongue:

-Tongue is a muscular organ covered by mucus membrane. (mucus

membrane=mucosa; epithelium + lamina propria).

-Muscles inside the tongue form bundles separated by connective

tissue continuous with that in the lamina propria.

-The dorsal surface of the tongue is covered by epithelium that shows

papilla. (specifically anterior 2/3rd s of the dorsal surface).

-The under surface of the tongue (ventral surface of the tongue) is

covered by non-keratinized stratified squamous epithelium.

*Note:

1) Anterior 2/3rd s of the tongue Keratinized stratified squamous

epithelium & it contains papilla.

2) Posterior 1/3rd of the tongue Non-Keratinized stratified squamous

epithelium.

3) Ventral surface of the tongue Non-Keratinized stratified squamous

epithelium.

-The sulcus terminalis marks the junction between the oral and

pharyngeal parts of the tongue. (the oral part: anterior 2/3rd s of the

tongue, and the pharyngeal part: posterior 1/3rd ).

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-Sensations from the anterior 2/3 of the tongue:

a) General sensations are carried by the lingual nerve, which is a

branch of the trigeminal nerve.

b) Taste sensations (special sensations) are supplied by the facial

nerve, more specifically by a special branch of it called Chorda

Tympani. (the facial nerve has a branch called chorda tympani,

which accompanies the lingual nerve.)

*Note: Lingual nerve originates from the trigeminal nerve, and Chorda

tympani originates from the facial nerve.

-All sensations (general &taste) from the posterior 1/3 of the tongue

are carried by the glossopharyngeal nerve, except the most

posterior part of the posterior 1/3rd and the epiglottis region (they

are carried by the vagus nerve).

-All muscles of the tongue receive motor innervation from the

hypoglossal nerve except the palatoglossus muscle (supplied by the

glossopharyngeal nerve).

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⁂Types of Lingual Papilla:

-Depending on what we have studied in Oral Histology, we have 4

types of lingual papilla: filiform papillae, fungiform papillae,

circumvallate papillae, and foliate papillae.

1- Filiform: found at the anterior 2/3rd s of the tongue dorsum ,

conical in shape, keratinized, and they don’t have taste buds. (in

filiform papillae, we can’t find taste buds because they are related to

mastication, not tasting). (Filiform papillae help in mastication

because of their roughness).

2- Fungiform: mushroom-like, contain taste buds in their apices.

(apices= top surfaces), and they are either slightly keratinized or non-

keratinized.

3- Foliate: poorly developed in humans, present on the dorsolateral

part of the anterior 2/3rd

s of the dorsal surface of the tongue,

contain many taste buds.

*Taste buds of the foliate papillae are found on the sides of grooves.

4- Circumvallate:

a) 8-18 in number in front of (anterior to) sulcus terminalis. (as

we said, sulcus terminalis is the junction between the anterior

2/3rd s and posterior 1/3rd ).

b) Have taste buds on their sides.

c) Each one is surrounded by deep groove (sulcus/trench).

d) Serous glands (Von Ebner (minor salivary glands completely

serous )) open in the bottom of the sulcus, and secrete watery

secretions that contain enzymes such as: lingual lipase.

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*Note: Circumvallate and

Foliate papillae are either

non-keratinized or slightly

keratinized, while filiform

papillae are keratinized.

*Note: Submucosa is only

of rdfound at the posterior 1/3

the tongue, while in the anterior

s of the dorsal area of rd2/3

tongue and the ventral surface

of the tongue we cannot see submucosa.

*This is a coronal / transverse

section of the tongue.

4: Muscles of the tongue.

1: Circumvallate papillae

surrounded by a trench(groove), and

associated with Von Ebner’s Gland.

(We can identify the taste buds at

higher magnifications).

2: Fungiform papillae: they are

smaller than circumvallate papillae,

they contain few taste buds on the

surface.

3: Filiform papillae. (Keratinized)

*We can notice here that there is a large

amount of keratin, and we can’t find submucosa

since submucosa layer is only found in the

posterior 1/3rd of the tongue.

1: Keratinized stratified squamous epithelium

(part of the filiform papilla).

2: Lamina Propria. (core of the papilla)

3: Muscle Layers. (There are multiple layers and

multiple directions of muscles in the tongue.)

1 1 2

3

3

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Red arrows →minor salivary

gland

Green→ muscle fibers

1 1 1 *This picture represents the posterior 1/3rd region

of the tongue. (because we can see submucosa).

*Non keratinized stratified squamous epithelium.

*Lingual tonsils are so clear in this area.

1: Lingual tonsils (lymphoid tissue); these lymphoid

tissues are found in 2 places:

a) In the lamina propria.

b) In the superficial part of the submucosa.

2: The deep layer of the submucosa contains Minor

Salivary Glands (Mucus type).

3: Muscle fibers that follow the underlying muscle

layer. (These muscle fibers are also considered parts of the

deep layer of submucosa).

2 2

2

2 3

3 3

*This picture shows the filiform type of

papillae.

-We can notice here that not all of filiform papillae

are conical in shape. In histological sections,

sometimes they appear broad instead of being

conical-shaped.

*The clearest thing that makes us

differentiate between filiform papillae and

other types of papillae is the thick layer of

keratin that the filiform papilla has.

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**Note: Minor glands don’t have striated ducts or major collecting ducts, but they have

intercalated ducts (intercalated are not so clear here) & minor ducts.

*Circumvallate Papilla. (slightly

keratinized in this picture).

1: The trench (sulcus/groove).

2: Taste buds.

1 1

2

2 2

2

*This is a section of a minor salivary

gland (specifically from the posterior

1/3rd of the dorsum of the tongue).

*Mucus glands(flat and basally

located nucleus ).

-Area (A): Fat/Adipose cells.

-The Arrows are pointing at: ducts.

*This picture shows the posterior 1/3rd of the

dorsum of the tongue “lingual tonsils”.

1: Crypt.

2: Lymphoid tissues. (Whenever we see lymphoid

tissues, we know that we are in the lingual tonsils

area.)

We can also see the fat tissues, minor salivary

glands “mucus”, and muscle fibers in the

deep part of submucosa.

1

2

2

2

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⁂Salivary glands:

-Glands are divided according to the nature of their secretions into:

1) Serous, example

2) Mucus, example: Only minor glands such as: the minor salivary

glands that are found in the posterior region of the oral cavity.

(minor salivary glands found in the posterior 1/3rd of the dorsum of

the tongue, in the soft palate, in the posterolateral region of the

hard palate, in the palatoglossal arch).

3) Mixed:

a) Mixed, mainly mucus (mucuserous): examples: sublingual

glands (major), minor salivary glands in the anterior region of

the oral cavity (lip, cheek(anteriorly), alveolar mucosa, anterior

lingual gland which opens at the ventral surface of the tongue at

its end).

b) Mixed, mainly serous (seromucus): example: Submandibular

gland.

into: duct systemsare divided according to their )eralin gen( Glands-

1) Simple: (duct system is unbranched), examples: Sweat glands,

Sebaceous glands.

2) Compound: All salivary glands are considered compound glands

because of the branching.

Major: Parotid gland.

Minor: Von Ebner glands.

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-Glands are divided according to their secretory parts into:

1) Tubular; coiled, branched.

In the salivary glands, if the secretory end-pieces were mucus, the

gland shall be tubular OR mixed (tubuloalveolar) in case of having

serous demilunes at their ends.

2) Alveolar (acinus/spherical); branched.

If the secretory end-pieces were serous.

3) Tubuloalveolar.

If the secretory end-pieces were mixed (Mucoserous or Seromucus).

**Some examples for further clarification:

-Glands are also divided according to their sizes into:

1) Minor salivary glands: distributed all over the oral cavity and

account for ~ 10% of saliva and most of the mucus secreted.

2) Major salivary glands:

a) Parotid: purely serous in humans.

b) Submandibular: seromucous.

c) Sublingual: mixed mainly mucus (mucus except for the

serous demilunes.)

-Parotid gland→acinar gland(serous).

-Von Ebner’s gland→acinar gland(serous).

-Mucus glands (mentioned

before)→ tubular glands.

*Any other gland except the mentioned above is considered tubule-acinar

(tubulo-alveolar). (pay attention that it must be mixed)

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⁂Major Salivary Glands:

•Each surrounded by a capsule of variable thickness.

•Septa divide the gland incompletely into smaller lobules.

•The duct system is branching (compound).

•The secretory part contains two types of cells: (in case of mixed

glands only): Mucus & Serous.

⁂Mucus Cells:

• Cuboidal(long) to columnar(short) in shape, sometimes pyramidal

in shape.

• Flat and basally located nucleus (pushed basally).

• Cytoplasm contains vesicles that contain glycoprotein (mucin)

Mucin is a highly glycosylated protein.

• Tend to be arranged in tubules.

*In the submandibular and sublingual glands the end of the tubule is

surrounded by a serous demilune*.

⁂Serous Cells:

• Pyramidal in shape.

• Have short irregular microvilli on the apical part.

• Typical protein synthesizing cells. (contain RER and Golgi

apparatus).

• Adjacent cells are joined by tight junctions.

• Cells are present in acini.

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⁂Myoepithelial Cells (Also known as Basket Cells):

• Surround the secretory end-pieces and intercalated ducts.

• “Myoepithelial” means that it is an epithelium which has a

contractile ability.

(Contractile ability: myoepithelial cells push the secretions from the

lumen of the secretory end-piece toward the intercalated ducts, and

from the intercalated ducts toward the larger ducts).

• Found between basal lamina and cells of the secretory parts and

beginning of ducts.

• Appear branched (basket cells).

• Resemble smooth muscles in function and appearance.

• Have junction with each other and with cells of the secretory

part.

• They support the secretory part and squeeze the secretions.

⁂Duct System:

Intercalated duct

• Smallest duct, cuboidal epithelium, high mitotic activity, differentiate into secretory and duct cells. (act as stem cells to regenerate secretory end-pieces)

Striated duct

• Only found in 2 glands: submandibular & parotid.

• Columnar cells with basal striations. (Basal Striations: in the basal area, there are some "folds" that give the duct its striated pattern)

Interlobular (excretory)

• Minor , major and main collecting ducts.

• Minor duct: Simple columnar epithelium.

• Major duct: Pseudostratified columnar epithelium.

• Main duct: Stratified columnar epithelium.

• At the end of the duct: resembles the oral epithelium (non-keratinized stratified squamous epithelium)

(Note: Intercalated ducts & striated ducts are called “Intralobular

ducts”)

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*This is a section taken from the Parotid

gland.

-The cells that contain rounded nucleus

are serous cells, but the cells that the

arrows are pointing at have flat nuclei,

which means that they are

myoepithelial cells. (remember that

myoepithelial cells surround the secretory

end-pieces and intercalated ducts).

Remember: (intralobular duct might be

intercalated or striated duct)

*This section is also taken from a

parotid gland, it is an intralobular

duct with simple columnar cells (remember: intercalated duct has

cuboidal or flat cells), so this is a striated

duct not an intercalated duct.

-We can notice the basal striations.

*Pseudostratified columnar epithelium.

So, depending on the information mentioned

in the previous page, we can know that it is a

Major collecting duct.

-Interlobular ducts (major,minor,main) have

large amounts of Connective Tissue. (The

blue color in this picture)

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*This is a section taken from a

submandibular salivary gland. (Mixed

mainly serous).

-When we want know the type of

gland, we only compare the secretory

end-pieces.

*Submandibular salivary gland

→ mixed mainly serous.

*This is a sublingual gland. (Mixed,

mainly mucus).

-The arrows are pointing at serous

demilunes (at the end of the mucus

end-pieces).

*Sublingual gland (Mixed, mainly mucus)

-We can see the large amount of CT (interlobular

ducts).

*Sublingual gland doesn’t contain main ducts. In

this picture we can clearly see major and minor

ducts (*exception*inter and intra minor collecting

ducts).

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*This Table is for memorization.

Parotid Submandibular Sublingual

Location Fills the space

between

mastoid process

and mandible

Below the mandible Floor of mouth

Classification Compound

tubuloalveolar Same Same

Stroma Dense capsule

and septa Less dense capsule

and septa No capsule, many septa and

lobules

Secretory

epithelium Serous Seromucous Mostly mucous (mucoserous)

Intercalated

ducts Long and

branched Similar but shorter Rare

Striated ducts abundant Same as parotid but

longer absent

Excretory

duct (Main) Stenson’s Wharton’s Bartholin’s (we said that

sublingual doesn’t have one

main excretory duct, it has

many major ducts, but this one

is the main Major duct).

Interstitial

tissue (with age,

all of them can

have accumulation

of fat)

Abundant

adipocytes Few or no adipocytes No adipocytes

function Lubrication of

food and partial

digestion of

carbohydrate

Same Same