Saliva I Flashcards
What are the functions of saliva and what is it?
Saliva is quite complex as a fluid Dilute aqueous solution of organic and inorganic compounds Numerous functions (Box 9.1) : - bolus formation, lubricant - buffer, solvent, minerals - enzymes, anti-bacterials - physiologically active substances
digestion
antifungal action
temperature regulation
Saliva is protective, the first barrier to what the oral cavity perceives as a hostile environment. Ppl with low salivary flow rates lose their dentition very quickly.
It’s hard to swallow something that is dry. It has glycoproteins that suck up water.
As flow rates decrease, buffer capacity decreases, and these are critical for integrity of your teeth.
There are growth factors in saliva.
How much saliva is secreted/day and what happens to most of it and what makes the saliva? How does it alter its composition?
~ 0.75L/ day (1/5 total plasma volume)
Most saliva is swallowed and reabsorbed by the gut
Saliva comprised of the exudate of all salivary glands (esp. major s.g.: parotid, submandibular, and sublingual glands)
Therefore, it alters its composition depending on whether saliva is analyzed at resting flow rates or at stimulated flow rates
salivary flow is lowest when you’re sleeping
What is one of the most important statements of saliva in regards to the acidity of the oral cavity?
WHEN YOU INCREASE THE FLOW RATE YOU DECREASE THE ACID!!!!!! THINK OF WHAT THIS WILL DO TO THE ORAL CAVITY!!!!!
What creates viscosity in the saliva?
1) Lubrication: What creates viscosity?
The major proteins that are manufactured in the salivary glands are glycoproteins (mucins) - viscous - polypeptide helix - carbohydrate side chain - large #’s of GP’s. are produced Sublingual - sulphur, sialate Submandibular - neutral, acidic DON’T NEED TO KNOW EXACTLY WHAT IT IS BUT IT IS A PROTEIN CARBOHYDRATE CHAIN – KNOW THIS. THEY SOAK UP WATER.
Don’t need to know these other names for like the sublingual and submandibular.
What is the function of most of the other proteins in saliva?
1) Lubrication:
The other proteins in salivary do impart some viscosity, but none are as effective as glycoprts in lubricating
- resist the action of proteolytic enzymes
- protect the epithelial wall of GI tract
Without these proteins, formation of bolus, swallowing and speech become very difficult
Resist the action of proteolytic enzymes, enzymes that like to break down tissues.
XEROSTOMIA!!!!!!!! its dry mouth
How does saliva aid in digestion?
Many of the proteins (enzymes) that give saliva its viscosity are also important in digestion of food particles
- Salivary amylase - Salivary Lipase - Peroxidase
Salivary amylase, breakdown carbohydrates
Lipase for fats
Peroxidase is antibacterial.
Are there more than one form s of salivay amylase (ptyalin)? What does it do?
Salivary amylase (ptyalin)
Enzyme responsible for breaking down starch, esp. in foods that have been degraded by cooking
Comes in two forms
a - amylase (a-1,4, glucan-4-glucanohydrolase)
b - amylase (found mainly in plants, bact.)
How does it work?
Starch is made up of 2 polysacharrides
amylose (this is 1-4 carbon linked)
amylopectin is the same as amylos except it has a 1-6 carbon linked part
a - amylase attacks the starch at the 1 - 4 carbon bonds between each glucose molecule
The end products of this digestion are glucose & maltose molecules and residual complexes of 1-6 carbon linked molecules - limit dextrans
What are the breakdown products of starch?
glucose, limit dextrans, maltose (2 glucose linked 1-4)
What is the optimal working pH of salivary amylase? how does this effect it and what does this mean for digestion?
Salivary amylase is a slow working enzyme that works at optimal pH of 6.8
Amylase become inactivated when in contact with stomach contents
Most carbohydrate degradation will take place in the stomach/ small intestine (pepsin)
So what is it more probable function?
Likely role of salivary amylase is break down residual food trapped in between teeth
Would expect that persons with higher levels of amylase would have higher incidence of caries
Why?
But compounded by other factors such as
Flow rate of saliva
Presence of acid producing bacteria
When you increase flow rate you increase amylase and you wash everything else.
What is one antibacterial action of saliva with mechanical action?
Mechanical actions of cheeks & tongue remove some adherent bacteria
Lack of this activity is most noticable first thing in the morning (oral horribilis)
The bacteria are suspended in the saliva and are generally swallowed/expectorated
Many surfaces are not cleansed by this action
That’s why tooth brushing is important.
What else is there about saliva that helps control bacteria?
What is another antibacterial function of saliva with mixture of all three glands?
When saliva becomes mixed (from all 3 glands) it develops “Leucotactic activity factor”
This factor helps attract polymorphonuclear leukocytes (PMN’s) to the saliva.
Strangely, the factor “Leucotaxin” is formed as a result of the action of bacterial proteolytic enzymes on the salivary proteins
What other antibacterial action does the saliva have in regards to immunoglobulins?
There are also immunoglobulins released from the capillary bed that permeate into the saliva
IgA > IgM > IgG
Form Opsonins that attach to bacteria surface membranes so that PMN’s can recognize as foreign and attack
what is an antibacterial action of saliva that involved bacterial cell walls?
There are enzymes in saliva that attack bacteria
Lysozyme (muramidase) dramatically attacks and dissolves certain bacterial cell walls - esp. those with polysacharrides
Depends on amount of mucin present as to effectiveness
Kills Micrococcus lysodeikticus well
Works more slowly against others - both cariogenic and non-cariogenic
What is an antibacterial action of saliva in regards to salivary bacteria?
Salivary bacteria also produce anti-bacterials
Why?
To antagonize/prevent colonization by other species
Produce hydrogen peroxide as well as lactic acid
What is an example of the antibacterial action of saliva in regards to hydrogen peroxide?
Another example
Salivary bacteria produce hydrogen peroxide
This combines with thiocyanate, present in small amounts in saliva
End result is formation of very effective but unstable bacteriocidal
Cyanosulphurous (ic) acid HO2SCN HO3SCN
What is an example of antibacterial action of saliva in regards to how well it performs as an antibacterial?
How well saliva performs as an antibacterial depends on many factors
Once bacterial species take hold, often the end result is an increase in cariogenic activity
This is due to production of acid
Streptococcus mutans, Actinomyces, Lactobacillus acidophillus
So what property does saliva have to combat this?
Flow rate and buffers is how it will combat this.
Why do we need a buffering capacity in our mouths?
Bacterial by-products are for the most part acidic
Many of the foods we eat are also acidic (drink)
High - fluctuations in pH would be detrimental to the health of the oral epithelium (as seen in xerostomic patients)
What are the 3 main buffering systems in saliva? Which is the most important?
There are 3 main buffering systems in saliva
Bicarbonate > phosphate > proteins
(proteins more involved in pH control in plaque)
Bicarbonate is the most important. This is why those with xerostomia end up with caries, it’s because of their lack of bicarbonate.
Why is bicarbonate buffering the most important? What is the reaction that takes place?
Bicarbonate Buffering - most important
Operates over a greater physiological range than other two
Saliva is saturated with bicarbonate ions
HCO3-
These are actively secreted in the saliva so as flow rates increase, so do amounts of HCO3- in saliva.
Combines with H+ to form weak carbonic acid
HCO3 + H –> H2CO3 —> H20 + CO2
bicarbonate to carbonic acid which is a buffer because it’s a weak acid.
What is the enzyme that helps bicarbonate HC03 to go to H2CO3 ?
HCO3- + H+ H2CO3
This reaction is assisted by an enzyme carbonic anhydrase and is driven further to form
H2CO3 H2O + CO2
End up with water & CO2 in the oral cavity - complete removal of acid - Resting pH of 6-7
Ratio of HCO3- /H2CO3 is 4.5 : 1
What does phosphate buffering do for the teeth?
Phosphate buffering
- not as critical for buffering as HCO3- but it is important physiologically for healthy teeth
The rate at which hydroxyapatite crystals of teeth dissolve depends on
1) the pH of the solution
2) levels of [PO43-] and [Ca2+] in solutn
At neutral pH, saliva is saturated with [PO43-] and [Ca2+]
Phosphate mops up excess hydrogen (acid)
As acid levels increase in saliva the following reaction occurs
Phosphate ion is the first part. PO4 + H –> HPO4 + H –> H2PO4
As [HPO42-] is formed, it complexes with free [Ca2+] ions to form brushite - precursor to calculus
An offshoot to the above formula is the one that goes to brushite.
Phosphate ion is the first part. PO4 + H –> HPO4 + Ca + H20 –> brushite CaHPO4 . 2H20
What does brushite do and what happens to levels of phosphate and calcium ? What happens when you don’t have enough phosphate ion or calcium ion in the saliva when the pH gets low?
Brushite - CaHPO4 . 2 H2O is insoluble and therefore precipitates onto tooth surface
What has happened to the levels of [PO43-] and [Ca2+] in the saliva though?
Where are these ionic levels replenished from?
- newly added saliva
As pH continues to decrease, get to acid level where [PO43-] and [Ca2+] removed from teeth
The pH level where [PO43-] and [Ca2+] removed from teeth is called the “critical pH” - usually about pH 5.5 (can be as high as 6.5)
At this point the inorganic material of the teeth is dissolved to provide enough [PO43-] to counteract the H+ ions in the acid
Calcium hydroxyapatite - Ca10(PO4) 6OH2 - in enamel and dentine is attacked
