salivary gland

what are salivary glands?

compound, tubulo-acinar, merocrine and exocrine glands whose ducts open into the oral cavity. they produce and secreted saliva

what is saliva composed of?

it is a complex fluid, consisting of 99%, alongside calcium (Ca), phosphate (PO4), fluoride (F), proteins, glycoproteins and enzymes. it is produced by salivary glands and has an important role in maintaing the overall health and normal condition of the oral cavity

what are the functions of saliva?

• protection

• buffering action

• maintenance of tooth integrity

• digestion

• defense (antimicrobial action)

• taste

• tissue repair

how does saliva protect the oral cavity?

• lubrication and acting as a barrier to microbial products

• washing action by removal of bacteria, its toxins and debris from the mouth. it also decreases the action if acidogenic bacteria by clearance of sugar

• via salivary pellicle

what is salivary pellicle?

a thin coat on the tooth surface that is formed by binding between calcium and protein

what is the active components in saliva that play a part in protecting the oral cavity?

• glycoprotein and mucins

• water

• protein and calcium

how does saliva act as a buffer for the oral cavity?

by maintaining the natural pH of the oral cavity

what is the active components in saliva that help maintain the pH of the oral cavity?

• PO4 (phosphate)

• bicarbonate

how does saliva help maintain tooth integrity?

1. post-eruptive maturation of enamel

2. repair and remineralization

3. protection by washing action

what is the active components in saliva that help maintain tooth integrity?

• calcium (Ca)

• phosphate (PO4)

• fluoride (F)

how does saliva aid in digestion?

1. bolus formation

2. digest starch into glucose

3. digest triglyceride into mono and diglyceride

4. neutralize esophageal contents

what is the active components in saliva that help with digestion?

1. water

2. amylase

3. maltose and lipase

4. phosphate (PO4) and bicarbonate

how does saliva help defend the oral cavity?

1. Hydrolyzes the cell wall of some bacteria.

2. Binds iron, an element essential for bacterial growth.

3. Immune defense via secretory IgA (bacteriostatic).

4. Acts as a physical microbial barrier.

5. Mechanical cleansing by washing action.

what is the active components in saliva that help with defense?

1. lysosomes

2. lactoferrin

3. lGA

4. mucins

5. water

how does saliva help in taste?

1. maturation of taste buds

2. washing taste buds from debris

what is the active components in saliva that help with taste?

1. protein gustin (taste bud protein)

2. water

how does saliva aid in tissue regeneration?

1. epithelial regeneration

2. wound healing

what is the active components in saliva that help in tissue repair?

growth factors

how are salivary glands classified according to their location?

1. glands of the oral vestibule

2. glands of the oral cavity proper

what are the glands of the oral vestibule?

1. labial gland

2. buccal gland

3. parotid gland

what are the glands of the oral cavity proper?

1. glands of the floor of the mouth

2. glands of the tongue

3. glands of the palate

what are the glands of the floor of the mouth?

1. submandibular glands

2. major and minor sublingual glands

3. glossopalatine glands

what are the glands of the tongue?

1. anterior lingual glands (Blandin nuhn)

2. posterior lingual glands (Von Ebner and weber glands)

what are the glands of the palate?

1. posterolateral of hard palate glands

2. soft palate glands

3. uvula glands

how are salivary glands classified according to their size?

1. major, which is parotid, sublingual and submandibular glands

2. minor, which are separated small mucosal glands in different areas of the mouth

where does the parotid gland open?

at the buccal vestibule, opposite to the upper molars

where does the sublingual gland open?

on each side of the lingual frenum

where does the submandibular gland open?

at the posterior part of the floor of the mouth

how often do major and minor salivary glands work?

major glands don’t act during sleep, while minor glands act 24 hours

how are salivary glands classified according to their nature of secretion?

• pure serous glands

• pure mucous glands

• mixed glands

what are pure serous secreting salivary glands?

1. von-ebner salivary glands (posterior lingual)

2. adult human parotid glands

what are pure mucous secreting salivary glands?

1. weber glands (posterior lingual)

2. anterior portion of anterior lingual glands (Blandin Nuhn)

3. minor sublingual glands

4. glossopalatine glands

5. palatine glands

no major glands secrete pure what?

mucous

what are mixed salivary glands?

1. mixed but predominantly serous

2. mixed but predominantly mucous

what are some mixed but predominantly serous secreting salivary glands?

1. parotid glands of newborns

2. 80% of submandibular glands

what are some mixed but predominantly mucous secreting salivary glands?

1. major sublingual glands

2. posterior portion of anterior lingual glands (Blandin-Nuhn)

3. buccal glands

4. labial glands

classification of parotid glands

• oral vestibule

• major gland

• pure serous in adults, mixed predominantly serous in newborns

classification of submandibular glands

• oral cavity proper

• major gland

• mixed, predominantly serous

classification of major sublingual glands

• oral cavity proper

• major

• mixed, predominantly mucous

classification of minor sublingual glands

• oral cavity proper

• minor

• pure mucous

classification of anterior portion of anterior (Blandin Nuhn) lingual glands

• oral cavity proper

• minor

• pure mucous

classification of posterior portion of anterior (Blandin Nuhn) lingual glands

• oral cavity proper

• minor

• mixed, predominantly mucous

classification of Von Ebner glands

• oral cavity proper

• minor

• pure serous

classification of Weber glands

• oral cavity proper

• minor

• pure mucous

classification of palatine glands

• oral cavity proper

• minor

• pure mucous

classification of glossopalatine glands

• oral vestibule

• minor

• pure mucous

classification of labial and buccal glands

• oral vestibule

• minor

• mixed, predominately mucous

what is the duct of the parotid gland?

Stenson’s duct

what is the duct of the submandibular gland?

Wharton’s duct

what are the ducts of the sublingual gland?

• Bartholin’s duct

• Revinous ducts, which are 8-20 in number

what is the histological structure of salivary glands?

1. framework of the CT elements, or the stroma, which consists of cells, fibers, ground substance and nerves

2. parenchymal elements, which consists of secretory cells (acini) which can be mucous or serous, and non-secretory cells, which consists of myoepith and oncocyte

3. duct system, which consists of secretory duct (intercalated or striated), excretory duct and main duct

what are the framework of the connective tissue elements in salivary glands?

a capsule is present, which surrounds and protects the gland. a septa extends inward to subdivide the glands into major lobes. each lobe is further subdivided into lobules. the connective tissue contains fibers, cells and ground substance. the connective tissue supports the blood vessels, lymphatic vessels and nerves that supply the gland

what are the parenchymal elements in salivary glands?

1. secretory cells (serous or mucous cells)

2. non secretory cells (myoepith. cells, oncocytes)

what are secretory cells?

also known as acini, they are clusters of secretory cells that vary in shape and size and resemble a many-lobed berry (grape-like cluster). they can either be serous, mucous, or mixed

what is the shape of serous acini?

sphere

what is the shape of mucous acini?

tubular long acini

what is the size of serous acini?

small

what is the size of mucous acini?

large

what is the lumen of serous acini?

narrow

what is the lumen of mucous acini?

larger

what is the shape of the cells in serous acini?

pyramidal, with the apex directed towards the lumen

what is the shape of the cells in mucous acini?

short cuboidal or flattened

what is the number of the cells in serous acini?

1 layer

what is the number of the cells in mucous acini?

1 layer or more

what is the shape of the nucleus in serous acini?

spherical

what is the shape of the nucleus in mucous acini?

flattened or angular

what is the site of the nucleus in serous acini?

basal thirds

what is the site of the nucleus in mucous acini?

compressed against basal cell membrane

what do serous cells synthesize?

protein enzymes, so cell shows features of protein synthesis, storage, secretion

what do mucous cells synthesize?

mucin

what color is the cytoplasm of serous cells when stained?

done by H&E, it is darkly stained basophilic due to abundant rough endoplasmic reticulum

what color is the cytoplasm of mucous cells when stained?

done by H&E, it appears pale, vacuolated/empty-looking because mucin does not stain well

what does the apical cytoplasm of serous cells contain?

zymogen secretory granules

what does the basal cytoplasm of serous cells contain?

basal striations due to numerous parallel RER

what does not appear empty in mucous cell cytoplasm when stained?

numerous mucigenic granules and thin film of cytoplasm, which forms a trabecular network

nucleus of serous cells

rounded basally

nucleus of mucous cells

compressed basally

what are the organelles of serous cells?

• Large amount of RER

• Prominent Golgi complex (basal/lateral to nucleus)

• Many mitochondria, lysosomes, microfilaments, microtubules

what are the organelles of mucous cells?

• fewer RER

• Large Golgi complex (10–12 prominent Golgi)

• Few mitochondria and microvilli

in serous cells, the intercellular canaliculi ends in the form of?

many junctional complexes and desmosomes

which cell types has very few intercellular canaliculi?

mucous cells

what is the exocytosis / secretion type of serous cells?

granule membrane fuses with cell membrane → membrane ruptures → contents released outside

what is the exocytosis / secretion type of mucous cells?

granules expelled with membrane intact → membrane later removed outside

what are some characteristics of myoepithelial cells?

• non-secretory cell type known as basket cells

• spindle shaped cell with 4-8 cytoplasmic processes

• found between basal surface of secretory cells/duct cells and the basement membrane. they are associated with secretory acini and intercalated ducts.

• attached to underlying cells by desmosomes

• contains many microfilaments which collect to form dark bodies

• cells organelles are peri-tubular

what are the functions of myoepithelial cells?

it has a contractile function which is decreasing the luminal volume, thus increasing the secretory pressure, thus

accelerating the initial flow of saliva.

what are oncocytes?

spherical large cells mostly found in ducts and represent an age-related change.

what is the histological features of oncocytes?

they are large and spherical cells, with pyknotic (small, shrunken and dark-staining) nucleus, placed centrally in the cell. their cytoplasm is strongly eosinophilic (pink with H&E stain) and they are rich with numerous mitochondria. they are located in ducts and are associated with old age

what is the duct system?

it is a varied network of tubules that progressively increase in diameter, beginning at the end piece and extending into the oral cavity

how are ducts divided?

1. secretory duct (intralobular) which includes intrecalated duct and striated duct

2. excretory duct (interlobular)

3. main duct

what are inter-calated ducts?

a type of secretory duct, it is the first portion of the duct. it is small in size and is difficult to see under a light microscope. it is numerous in watery secreted glands (serous)

what is the structure of intercalated ducts?

they are lined by a single layer of low cuboidal cells with a centrally placed nucleus, and little cytoplasm

what are the functions of intercalated ducts?

1. the cells of the proximal part have a secretory function

2. its cells contain a protein that has antibacterial function, known as lactoferrin

3. it acts as a stem cell reservoir, meaning it can regenerate and replace damaged cell in end pieces and striated ducts

where does saliva from intercalated ducts drain?

into striated ducts

what is the structure of striated ducts?

• it is a single layer of high columnar cells. it has a central nucleus and a large amount of pale, eosinophilic cytoplasm

• its cells show a striation at the basal end due to membrane folding, with numerous mitochondria located in between

• adjacent cells are connected by junctional complexes and desmosomes, which hold the cells tightly together.

• luminal surfaces contain microvelli

what are the functions of striated ducts?

1. they modify saliva passing through them

2. they actively reabsorb Na and Cl ions and secrete K and bicarbonate in primary secretion, which changes changes saliva from isotonic (or hypertonic) to hypotonic.

3. contains lysozymes, which have an antibacterial effect

4. concentrates iodine

5. adds amylase enzyme from the serum to the saliva.

what is the excretory duct?

an inter-lobular duct that is located outside the lobules, in the connective tissue septa that separate the lobules. they are larger in diameter than striated ducts

what is the structure of excretory ducts?

• they are lined by pseudostratified epithelium, containing scattered goblet cells.

• cells towards the striated duct is tall columnar epithelium

• cells towards the are stratified squamous epithelium

• they are attached to the basal lamina by hemi-desmosomes

what are the functions of the excretory duct?

1. transports the salivary secretion towards the oral cavity

2. they have the ability to reabsorb Na, Cl and to secrete K and bicarbonate, producing hypotonic saliva.

as the excretory duct approaches the oral cavity (mouth), its lining (epithelium) changes to what?

non-keratinized stratified squamous epithelium.

the main duct opens into the oral cavity through an opening called?

duct orifice