Salivary Glands Module 1 Flashcards
severe hyposalivation
increase incidence of caries is often seen in patients with reduced salivary flow
what causes reduction in salivation?
head and neck radiotherapy
autoimmune disease
sjogren’s syndrome
what does scintigraphy test?
salivary function
how is scintigraphy test done?
pt injected intravenously with radioactive compound that emits gamma radiation, allowing it to be visible radiographically and it binds to the ion membrane transport system of salivary and other gland cells
what glands show up normally with scintigraphy?
thyroid gland, parotid gland, submandibular gland, minor glands of soft palate and pharynx, nasal mucous glands
what do patient with congenital salivary aplasia lack?
radioactivity in parotid and submandibular glands, and minor glands affected.
what is agenesis?
lack of development (in this case- both sets of salivary glands)
genetic abnormalities of major salivary glands
rare
may involve single or multiple glands
may occur in isolation or with other developmental abnormalities of ectoderm or 1st brachial arch
severity of symptoms dependent on number of salivary glands involved and type of abnormality
early diagnosis and implementation of strategies to prevent caries is critical
what function does mucins perform in saliva?
protection
highly glycosylated glycoproteins that are viscous and largely responsible for lubricating the mucosal surface and providing a protective barrier.
also important for trapping bacteria and sugar and therefore providing for their clearance
what function does bicarbonate perform?
buffering
secreted in saliva and serves an important function in buffering acids in the mouth
what do proline-rich proteins and statherin do?
tooth integrity
calcium-binding proteins that allow saliva to be super saturated with calcium and contribute to enamel maturation and remineralization
what do lysozyme, peroxidase, defensins and histatins and igA do?
antimicrobial
contribute to direct antimicrobial functions of saliva- capable of antibacterial, antifungal and antiviral actions
what do growth factors do? example?
tissue repair
saliva participate in tissue repair by secreting growth factors like epidermal growth factor and nerve growth factor (NGF)
how do mucins contribute to digestive process?
mucins critical to chweing and swallowing food
how do enzymes like amylase and lipase contribute to digestion?
amylase- dissolve starch
lipase break down fats into free fatty acids and glycerol
how is saliva vital for the proper function of taste?
tasty molecules must first be dissolved in the water in saliva so that they can be transported to taste buds
also evidence that proline-rich proteins can bind certain food molecules and modify taste properties- ex. bind tannins in tea or red wine- lead to dry puckery feeling in mouth
what are salivary glands classified as?
exocrine glands
what are exocrine glands?
they discharge their secretion via a duct to an epithelial surface
what are other exocrine glands?
sweat or sebaceous glands of skin
how does exocrine glands contrast with endocrine glands?
endocrine glands like thyroid glands discharge secretions into blood stream without duct
what is normal daytime flow rates and volume of saliva in mouth in absence of stimulation induced by chewing or taste?
.3-.4ml/min
0.8-1.1ml saliva
most of it is in a thin film that coats mucosa and teeth
when does flow rates decrease?
during sleep meaning prebed time oral hygiene is critical
what are three major salivary glands and innervation ?
parotid gland- 9, submandibular-7, sublingual-7
what are minor glands and innervation?
von ebner’s gland- 9
labial, palatal, buccal lingual glands
what gland contribute the most volume of saliva?
parotid gland- 60%
submandibular- 25%
and submandibular and minor- 7-8%
what does the parotid gland secrete?
pure serous gland- secretes water saliva and main source of enzyme, amylase- which initiates breakdown of starch
what are submandibular and sublingual glands?
mixed serous and mucous glands
what are von ebner’s gland?
pure serous gland and source of lingual lipase- enzyme that breaks down triglycerides into free fatty acids
what are the other minor glands?
pure mucous glands- major source of mucins, glycosylated proteins critical for lubrication
what is the largest salivary gland?
parotid gland- 14-28g
where is the parotid gland?
sits superficial to the caudal end of the masseter muscle
how are parotid gland saliva discharged?
thru stenson’s duct opposite 2nd max molar
how much does the submandibular gland weigh?
10-15g
where does the submandibular gland sit?
anterior end wraps around the caudal end of mylohyoid muscle
where does submandibular gland empty into?
duct travels superficially to empty into the oral cavity via wharton’s duct on lingual frenum
what is the smallest duct?
sublingual duct- 2g
where does the sublingual duct empty into?
sublingual fold behind wharton’s- bartholin and rivinus’ ducts
what are salivary glands made up of?
stroma and parenchyma
what does stroma do?
supporting role- provide structural support to gland, forming capsule and organize gland into lobes
what does parenchyma do?
chracteristic work of a given gland- make the saliva and take care of discharging it to its final destination
what is stroma made up of salivary gland?
connective tissue
what is parenchyma made up of in salivary gland?
epithelium
what does the stroma include?
capsule that encompasses the salivary gland and separates it from surrounding tissue and septa which divides gland into lobes (major larger division) and lobules (minor smaller division)
what is the major cell type in salivary gland?
fibroblast- makes collagen- major component of ec matrix
what else does stroma contain and who do they do?
blood vessels- supply parenchyma-both acinar cells and ducts are supplied
nerve fibers- supply parenchyma- mainly the acinar cells and myoepithelial cell
plasma cells-secrete antibodies- IgG-
fat cells- increase with age
what are parenchyma comprised of?
secretory endpieces- acini
AND ducts
what are acini composed of?
individual acinar or secretory cells- these cells make saliva
what are the 3 types of endpieces?
serous (parotid)
mucous (minor)
mixed (submandibular and sublingual)
what does acini open into?
ducts- which get progressively larger toward oral surface
what is the progress of saliva in ducts?
intercalated ducts- striated ducts (secretory ducts)- into excretory ducts
when does salivary gland begin development?
6 week IU
when does parotid gland develop?
week 6 IU
when does submandibular gland develop?
week 6 IU at end
when does sublingual and minor glands develop?
weeks 8-12 IU
what is the origin of the parenchyma?
parotid- ectoderm
submandibular- ectoderm or endoderm
minor- endoderm
what is the origin of the stroma?
neural crest
what are the stages of salivary gland development similar to odontogenesis?
thickening of ectoderm or endoderm
formation of epithelial bud
important signals are exchanged between epithelial and mesenchymal compartments
what are the stages of salivary gland development different from odontogenesis but similar to other branched structures?
single bud branches then branches again and again and par of the branching structure ultimately becomes the ducts- hollows out in process called cavitation
what happens before branching occurs?
each cell is joined to its neighbors by cell adhesion molecules expressed on adjoining cell surfaces
what is an important cell adhesion molecule?
e-cadherin
what happens as cleft begin to form and progresses?
cadherin staining break up and disppears at base of cleft as clefting progresses
what finally happens?
e cadherin gone on surfaces of all cells that face the cleft
what is the cell doing to the adhesion molecule?
adhesion molecule remains on other surfaces of very same cells- cell not turning off adhesion molecule but redirecting its expression
what is one mechanism that control clefting?
suppression of ecadherin expression in certain region of the cell
what is a critical molecule to clefting?
cleftin
cleftin knocked down by sirna- gland much less branched - although some branching does occur
what induces expression of cleftin?
ex matrix molecule- fibronectin through fibronectin interact with fibronectin receptors on membranes of salivary gland cells
what are the 2 actions of cleftin expression? where does it take placE??
within the cell
acts to suppress the expression of e-cadherin expression but it upregulates expression of another molecule called snail 2
what is snail 2?
transcription factor important in many aspects of development and also cancer. unclear what it does to salivary glands but hypothesis- promotes a change in cell shape that coupled with e-cadherin- allows gaps to form
salivary physiology
acini secrete saliva
ducts secrete and resorb certain components present in salivary secretion
what does acinar cells secrete?
primary secretion or saliva-
water- host of proteins and ions- including sodium and chloride
what is primary saliva?
isotonic
are acinar cells water permeable?
yes
are duct cells water permeable
no
what do duct cells resorb and absorb?
resorb sodium and chloride
secrete few proteins and bicarbonate ions
fluid now called secondary secretion or saliva
what is secondary saliva?
hypotonic
how is salivary secretion controlled?
neural control
is that similar to secretions by other glands?
no- thyroid secrete thyroxin- controlled by blood borne hormones
how is salivary glands supplied?
by both branches of autonomic nervous system- sympathetic and parasympathetic
where are the cell bodies of pregang parasympathetic neurons located?
brainstem and send axons out to the brain in 7th and 9th cranial nerves which synapses on post gang neurons near each of the glands
where does the sympathetic supply originate from?
cell bodies of IML (intermediolateral nucleus) of the spinal cord which send axons out the cord to synapse in superior cervical ganglion and axons arising from post gang neurons in superior cerivical ganglion supply glands
what is sympathetic nervous system responsible for?
protein secretion.
post gang neuron releases norepinephrine which binds to a beta adrenergic receptor on the salivary acinar cells. this is a g-protein coupled receptor which is coupled to the enzyme adenyl cyclase/ activation of adenyl cyclase upregulates cAMP which activates PKA. PKA phorphorylates the secretory granules that contain synthesized proteins, facilitating their release
what does activation of the sympathetic nervous system alone produce?
protein laden, viscous secretion that is not voluminous
what is the parasypathetic nervous system responsble for?
fluid secretion and accounts most for the volume of saliva.
what happens when parasympathetic ns is activated?
post gang neuron releases acetylcholine which binds to a muscarinic type receptor on salivary acinar cell. also a g couple protein receptor- coupled to phospholipase c- which liberates IP3 from membrane phospholipids and liberates calcium from er
what happens with increase in calcium?
opens a chloride channel and conc gradient drives chloride from the cell- increasing cl- in lumen and creates electrical and osmotic gradient which draws sodium and water via a between cells pathway
how is chloride maintained at high conc intracellularly?
energy requiring ion pump
