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Saliva - composition + secretion Flashcards

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1
Q

list the 5 roles saliva is important in

A

1) lubrication
2) maintenance of oral hygiene
3) maintaining tooth mineralisation
4) digestion
5) solvation

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2
Q

important lubricant: which property makes saliva able to be a lubricant

A

mucous content

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3
Q

important lubricant: where is this important

A

speaking (speakers often have water because mouth can dry up)
eating

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4
Q

important lubricant: what does saliva do when eating

A
  • surrounds food
  • assists its passage down the oesophagus
  • if taste is bad = lots of saliva secreted to dilute it
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5
Q

important lubricant: what happens when we drink hot drinks

A
  • the hot solution mixes with saliva

- so it is diluted and cooled

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6
Q

maintenance of oral hygiene: which enzymes are contained in saliva and aids its antibacterial actions

A

lysozyme
- attacks bacterial cell walls
peptidases + peroxidases etc…
- destroy bacteria

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7
Q

maintenance of oral hygiene: what does saliva wash out

A

food particles between teeth

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8
Q

maintenance of oral hygiene: what is lactoferrin

A
  • found in saliva
  • an iron collator
  • removes iron
  • prevents bacteria growing as they require iron to do so
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9
Q

maintaining mineralisation: how does saliva achieve this

A
  • neutralises acid (corrosive to teeth) from vomiting or eating acidic food
  • inorganic compounds (ie Ca, F) are secreted into it and are incorporated into teeth to maintain mineralisation
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10
Q

maintenance of oral hygiene: what is xerostomia

A

dry mouth
can inc cavity risk
saliva can protect teeth by preventing its onset

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11
Q

digestion: which digestive enymes are contained in saliva

A

amylase (PTYALIN in saliva)

  • alpha amylase (1,4-glucan 4-glucanohydrolase) = main protein + digestive enzyme in saliva
  • carbohydrate break down

lipases (LINGUAL LIPASE in saliva)

  • only activated at pH 4 as food moves to stomach
  • fat break down
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12
Q

maintenance of oral hygiene: why isnt this function vital

A

digestion would still occur in stomach or small intestine if these enzymes weren’t present

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13
Q

solvation: what is role of saliva in solvation

A
  • dissolves and washes away food particles from tastebuds

- allows next mouthful of food to be tasted

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14
Q

what are the 3 major salivary glands, the % of saliva secreted they make up and what type of saliva they produce
give their locations

A
  • parotid (25%, serous) - near angle of jaw + ear
  • submandibular (70%, sero-mucin) - just below jaw
  • sublingual (5%, mucin) - beneath tongue
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15
Q

what type of secretion is saliva

A

exocrine (from a ductal system)

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16
Q

what is serous saliva

A
  • thin watery

- contains proteins from serous cells

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17
Q

what are mucins

A
  • family of glycoproteins
  • make up mucus (highly viscus fluid)
  • produced from mucus cells
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18
Q

what amount of saliva is produced daily

A

1500ml

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19
Q

what are acini

A

ball like clusters of epithelial cells in salivary glands

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20
Q

what do acini epithelial cells secrete

A

primary secretion

- mainly water, electrolytes, inorganic ions and enzymes

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21
Q

what happens to primary secretion

A

composition modified by secretion from epithelial cells lining the duct (they secrete or remove ions + h2o)

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22
Q

what is salivon

A

functional unit of a salivary duct

contains a blind end (ACINUS) comprised of acinar cells so secretes primary secretion

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23
Q

how is the rate of fluid secretion from the salivon influenced

A

myoepithelial cells surrounding acinar cells contain smooth muscle so contract + relax

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24
Q

where does fluid move to from the acinus

A

through intercalated ducts (area responsible for controlling rate of saliva secretion)

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25
how is fluid flow influenced in intercalating duct
- cells lining it contain smooth muscles - restrict fluid flow by constricting to dec size of lumen - increase fluid flow by dilating
26
what does the intercalated duct widen to become
the striated duct (lined by COLUMNAR epithelial cells)
27
what happens in the striated duct
the most modification to the primary secretion
28
where does fluid flow after the striated duct
excretory duct
29
what are the 3 main constituents of saliva
1) water 2) electrolytes 3) enzymes
30
which ions / electrolytes does saliva contain in high and low levels relative to plasma
``` high - K+ - HCO3^- low - Na+ - Cl- ```
31
what sort of process is saliva secretion, how
2 step 1) primary secretion - from acini - similar composition to plasma but also contains mucin + digestive enzymes 2) secondary secretion - takes place in striated ducts - modifies the composition
32
what else takes place and modifies the composition
absorption
33
what happens during secondary secretion
- Na+ and Cl- reabsorbed from duct - K+ and HCO3^- secreted in but to lesser extent - SO saliva becomes HYPOtonic (previously isotonic)
34
why does saliva become hypotonic
- ductal epithelium has low permeability to water | - water NOT reabsorbed therefore becomes hypotonic
35
explain the two-stage hypothesis
in the acinus - water, electrolytes, Na+, Cl-, HCO3^- enter - this is ISOTONIC primary secretion as it moves into striated duct - lot of Na+, Cl- reabsorbed - more K+, HCO3^- secreted by cells lining the duct BUT not enough to balance ions leaving so normally - H2O moves out of duct - but duct impermeable to H2O so get hypotonic solution
36
what is hypotonic solution of saliva
- dilute - lots of K+ and HCO3^- - less Na+ and Cl-
37
how is sodium reabsorbed into the epithelial cells across the apical membrane (lines lumen of the duct)
via the ENaC channel (epithelial sodium channel) and sodium-hydrogen exchanger
38
once reabsorbed, how does sodium exit into the interstitial space across the basolateral membrane (lines interstitial space)
uses the Na-K pump
39
how is Cl- reabsorbed into the epithelial cell across the apical membrane
via the apical | Cl- - HCO3^- exchanger
40
how does Cl- exit epithelial cell across the basolateral membrane into the interstitial space
down apical chloride channels
41
how is bicarbonate secreted from the epithelial cell, across the apical membrane into the lumen of the duct
via the Cl- - HCO3^- exchanger
42
how does bicarbonate enter the epithelial cell
unsure | basolateral step not well understood
43
how does potassium secretion occur via the salivary duct transporters of the epithelial cells
begins w basolateral uptake of K+ via Na-K pump followed by exit of K via apical K-H exchanger
44
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45
what does the final composition of saliva depend on
rate of secretion (as flow rate changes, ionic composition changes)
46
what is the composition of saliva at high flow rate
- similar electrolyte concs to plasma - composition similar to primary secretion - not enough time for secondary modification (reabsorption/secretion) to take place - except for bicarbonate
47
why is concentration of bicarbonates higher than plasma at high flow rates and why is this a good thing
- its transport is strongly influenced by stimulants of salivary secretion - important because it is alkaline SO when need high flow rates (ie when about to vomit / eaten acidic food - require large amount of saliva to neutralise acid + protect teeth), our saliva is alkaline due to large amounts of bicarbonate
48
what is salivary composition at low flow rates
- hypotonic solution - much less Na+ and Cl- as its resorbed - more K as its secreted - time for secondary modification (reabsorption/secretion) to occur
49
what 4 experiments provide evidence for two-stage hypothesis
1) flow rate curves 2) acinar/intercalated duct micropuncture 3) transport properties of isolated, perfused ducts 4) polylysine injection
50
how are flow rate curves created
- measure salivary flow rate under different stimulants | - look at electrolyte concentrations within them
51
how is duct micropuncture carried out
1) note composition independent of flow rate 2) do micropunture 3) look at flow rate
52
what does poly-lysine injection do
1) poisons ducts 2) inhibits secondary reabsorption process 3) saliva becomes like primary fluid
53
which system controls rate of salivary flow / secretion
autonomic nervous system (split into parasympathetic and sympathetic systems)
54
what does stimulation of BOTH the parasympathetic AND sympathetic systems do
increase saliva secretion
55
explain the role of the parasympathetic stimulation
- largest role | - involved in production of copious flow of watery saliva and vasodilation
56
how does parasympathetic stimulation increase salivary secretion
1) release acetylcholine (neurotransmitter) 2) acts on muscarinic receptors 3) causing contraction of myoepithelial cells surrounding the acinus 4) so acinus expels more saliva
57
what else is released upon parasympathetic stimulation
vasoactiveintestinal peptide (VIP) 1) causes vasodilation 2) increasing blood flow and o2 delivery 3) allows increased secretion
58
explain the role of the sympathetic stimulation
- produces small amount of more mucus + enzyme rich saliva
59
how does sympathetic stimulation increase salivary secretion
1) releases adrenaline and noradrenaline 2) these act on adrenoreceptors 3) causes myoepithelial cells to contract
60
why is the autonomic nervous system activated / how does the body know we require saliva?
1) physical things 2) higher brain centres (involuntary effects) 3) prior to sickness, nausea, water brash
61
which physical things activate the ANS reflex stimulation and secretion
- food in mouth | - chewing
62
how do higher brain centres stimulate ANS | give an example
- conditioned reflex - stimulation comes from higher brain centres rather than food itself - ie Pavlov's dogs with the bell
63
how do sickness, nausea or water brash stimulate the ANS
- reflux of acid coming up oesophagus stimulates excessive secretion of alkaline saliva - this neutralises stomach acid, protecting the teeth
64
what is the name of the part of the brain responsible for sending signals out via to ANS to increase/decrease production
salivary centre
65
how does the salivary centre work
1) detects various signals which it acts on ie physical (smell / taste of food, food in mouth, chewing) higher brain centres (fear, dehydration, excessive exercise, mental concentration= dec saliva production) or conditioned events 2) whatever the input it sends a signal through the parasympathetic or sympathetic nervous system

IOE (22 decks)

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