HNS31 Salivary And Nasal Secretion Flashcards
Salivary glands
Exocrine glands: produce saliva through system of ducts
3 Major pairs
- Parotid gland (15-20% resting salivary content in oral cavity)
—> Parotid duct
—> Opening at upper 2nd molar teeth - Submandibular gland (65-70% of resting salivary content in oral cavity)
—> Wharton duct
—> Opening at area beneath tongue - Sublingual gland (3-5% resting salivary content in oral cavity)
—> Sublingual ducts
—> Several openings at area beneath tongue
Function:
- Lubricating
- Protective
Minor gland (800-1000):
- Bucca
- Labia
- Lingual mucosa
- Soft palate
- Floor of mouth
Function:
1. Hydrating mucosal surface
High salivary flow vs Low salivary flow region
High salivary flow region (Salivary highway):
- Maxillary
- Mandibular
Low salivary flow region (Salivary byway) —> Dental caries formation:
- Maxillary anterior
***Salivary glands secretion
Parotid:
- Serous (contain enzymes) (watery)
- Acini: Serous acinus
Submandibular:
- Mixed serous + mucous
Sublingual:
- Mucous
- Acini: Gianuzzi demilune
Serous vs Mucous
Serous:
- **Zymogen granules (inactive enzyme) —> stain **darkly by eosin
- ***Round nuclei
- Secrete proteins in ***isotonic watery fluid
Mucous:
- Stain ***lightly, appears empty
- Bubbly shape
- ***Flattened nuclei lie against basement membrane
- Secrete ***mucin (mucoglycoprotein) (lubricant) —> squeeze nuclei to one side
Myoepithelial cells
Surround:
- End of secretory piece (acini)
- Ducts
Function:
- Prevent distension of end secretory piece
- Contract when gland is stimulated —> aid expulsion of saliva
***Salivary ducts
Intercalated duct (先):
- Cuboidal cell: secrete
1. Lactoferrin
2. Lysozyme
Striated duct (後):
- Cuboidal cell with **deep infoldings of basal plasma membrane (with **numerous mitochondria within)
—> deep infoldings: for ***Reabsorption of NaCl
—> mitochondria: energy used for electrolyte transport
Saliva composition
pH 6.2-7.4 (mainly alkaline unless acid production due to ingestion)
—> ***Alkaline: Re-mineralisation of enamel + Neutralise acid byproducts by microbes
***Hypotonic —> allow taste for salt
- Water (99.5%)
- Solids (0.5%)
- Organic substances
—> Enzymes (Amylase, Lipase, Lysozyme)
—> Others (Mucin, Lactoferrin, Agglutinin, IgA/G/M, Nitrogenous products e.g. urea, ammonia) - Inorganic substances
—> Na, K, HCO3, Cl, Ca, PO4, F
—> Ca, PO4: re-mineralisation
—> F: Fluoroapatite coat teeth to prevent caries formation
***Saliva functions
- Hydration and lubrication of oral tissues
- mucin
- water - Facilitate mastication and deglutition
- mucin (highly adhesive)
- water - Solubilisation of food —> enhancement of taste
- water
- hypotonicity - Initiating digestive process
- **Amylase
- **Lipase
- NO protease - Anti-bacterial —> oral hygiene and health of teeth
- **Lysozyme
- **Lactoferrin —> remove iron (iron-binding) which is required by bacteria
- Agglutinin —> aggregate pathogens
- IgA, G, M —> facilitate phagocytosis
***Salivary production - Electrolyte and Water
Water and electrolyte secretion: Energy consuming 2-stage process:
Stage 1 (in **Acini): **NaCl + **H2O secretion —> Isotonic primary saliva (~plasma fluid)
- **G protein coupled receptor (muscarinic receptor by PNS) stimulated
—> Ca signaling pathway
—> Ca-activated Cl channels (apical membrane of acinar cells)
—> Cl move into lumen
—> Na paracellular transport into lumen via leaky tight junctions
—> H2O paracellular transport into lumen via leaky tight junctions / Transcellular H2O transport via Aquaporin 5 (AQP5) (apical)
Cl from:
- Na/K-ATPase —> pump out Na —> Na go back via NKCC channel —> bring along Cl
(K go out by Ca-activated K channel on basolateral)
Ion channels related:
- ***Na/K-ATPase (basolateral)
- ***NKCC (basolateral)
- Ca-activated K channel (basolateral)
- ***Ca-activated Cl channel (apical)
- ***AQP5 (apical)
- ***Paracellular route (Na + H2O)
Stage 2 (in **Ducts): **NaCl reabsorption + ***KHCO3 secretion by ductal cells —> Hypotonic final saliva
- Ducts: impermeable to H2O (H2O cannot go back to interstitial space)
- Na reabsorption via ENaC (epithelial Na channels) (apical membrane of striated duct + excretory duct)
- Na/HCO3 co-transporter (NBC) (basolateral)
—> Na / HCO3 into cell
—> HCO3 exit into lumen via Cl/HCO3 exchanger (apical)
—> Cl into cell
—> Cl goes into interstitial space via electrogenic Cl channel (basolateral) - Na/K-ATPase (basolateral) —> K accumulation in cell —> K efflux into lumen via K channel (apical)
Ion channels related:
- ***ENaC (apical)
- ***Cl/HCO3 exchanger (apical)
- K channel (apical)
- Na/K-ATPase (basolateral)
- ***Na/HCO3 co-transporter (basolateral)
- Electrogenic Cl channel (basolateral)
Protein secretion from Salivary glands
3 main modes of vesicular protein secretion
- Regulated secretion (80-90%, 要有stimulation先release)
- stimulation of SNARE (SNAP receptor) (PKA cAMP pathway)
—> membrane fusion
—> secretion by secretory granule via exocytosis - Constitutive secretion (傳統, 不受stimulation影響)
- transcription + translation —> packaging in Golgi —> exocytosis - Transcytosis
- only for secretion of ***Ig complexes (produced by plasma cells around CT surrounding ducts)
Transcytosis mechanism
- Dimeric IgA released by plasma cells into interstitial matrix of salivary glands
- Dimeric IgA bind to polymeric Ig receptor (pIgR) (basolateral membrane of ductal epithelial cells)
- Internalisation and transport to luminal surface (dimeric IgA + pIgR)
- pIgR is cleaved and secretory IgA released into saliva
- secretory IgA still has part of pIgR —> prevent digestion in acidic environment
***Regulation of salivary secretion
Unstimulated rate: ~0.3 ml/min (majority by submandibular gland)
Stimulated rate: ~7 ml/min (majority by parotid gland)
3 specific triggers: 1. Mechanical (chewing) 2. Gustatory 3. Olfactory —> control salivary secretion via Autonomic NS (regulate both Volume + Type of saliva)
**Parasympathetic stimulation (rest and digest)
—> via ACh muscarinic M3 receptors (GPCR —> PLC —> IP3 —> Ca signaling pathway)
—> **watery saliva secretion (Fluid + Electrolyte)
**Sympathetic stimulation
—> via β adrenergic receptors by NA (GPCR —> cAMP —> PKA pathway)
—> **protein-rich saliva secretion (Mucin)
—> ↑ viscosity —> dry mouth
BOTH stimulation causes ***myoepithelial cell contraction
—> BOTH facilitate saliva secretion
***Nerve supply to salivary gland
SNS (“Thoracolumbar outflow”):
- Preganglionic neurons: T1-T4 of Intermediolateral cell column (i.e. Lateral horn)
—> **Superior cervical ganglion
—> Postganglion neurons pass through **External carotid artery plexus and its branches
—> ALL 3 salivary glands
PNS (“Craniosacral outflow”): 1. Superior salivatory nucleus (medulla) (記: CLS) —> Preganglionic neuron (CN7) —> Intermediate nerve —> ***Chorda tympani —> ***Lingual nerve (branch of CNV3) —> ***Submandibular ganglion —> Submandibular, Sublingual gland, Minor salivary glands of mouth, pharynx, nasopharynx
2. Inferior salivatory nucleus (記: LOA) —> Preganglionic neuron (CN9) —> Tympanic nerve plexus —> ***Lesser petrosal nerve —> ***Otic ganglion —> ***Auriculotemporal nerve (Postganglionic cell) (branch of CNV3) —> Parotid gland
Afferent signals to Salivary nuclei
- Taste buds (gustatory-salivary reflex)
- Anterior tongue (CN7)
- Posterior tongue (CN9)
—> Nucleus solitary tract
—> Salivary nuclei - Olfactory receptors (olfactory-salivary reflex)
- CN1
—> medial olfactory area
—> descending pathways from cortical centres
—> Salivary nuclei - Mechanoreceptors (masticatory-salivary reflex)
- CN5
—> Trigeminal nucleus
—> Salivary nuclei
After afferent signals received —> either PNS / SNS activated —> visceral motor output
3 major segments of Nasal cavity
- Squamous mucosa (stratified squamous) (入口)
- Respiratory mucosa (largest) (大部分)
- Olfactory mucosa (頂部)
