Teeth and Saliva
Teeth
Humans as Omnivores
Digestion is the breaking down of food - until it is so small that it can be absorbed
The purpose of the teeth in this process is:
To bite the food into a size that can be swallowed
The mechanically break down the food until it is a much called a bolus.
This is done to make the food easier to swallow
To increase the surface area of the food available for chemical digestion
There are 3 types of teeth
Incisors - these are like Scissors - they cut things - we use these to bite a sandwich or an apple
Canines - these are the big pointy teeth that dogs also have - we use them to tear meat when we heat with out using a fork and knife
Molars - these are the flat ones that Moo Cows also have - we use these to chew our foo
If we look in the human mouth we will see that we have 5 Molars on each side - so 10 on the bottom and 10 on the top. A grand total of 20!
We have 1 Canine on each side - so 2 on the bottom and 2 on the top. So a total of 4
And 2 Incisors on each side, so 4 on the bottom and 4 on the top. A grand total of 8.
If we add these up
Molars = 20
Canines = 4
Incisors = 8
Total teeth = 32
The big two Incisors in the middle of your smile, both at the top and at the bottom are called the Central Incisors (total of 4)
The tooth next to each Central Incisor is called a Lateral Incisor (total of 4)
The Canines are just Canines. Sometimes they are called Cuspid - a Cusp is a bump on the tooth and the Canines are one big bump so they can be called Cuspid
The Molar right next to the Canine is called a Premolar. The tooth next to the first premolar is the second premolar
The premolars are easy to spot because they are smaller. They are sometimes called bicuspid - this is because they have 2 bumps
We have a total of 8 premolars
Molars are easy to spot as they are big
They hare 4 or 5 cusps
The first molar is called the first molar
The second molar is called the second molar
The third molar is called the wisdom tooth - because it usually doesn't arrive till you are in your twenties and are 'wise'. These teeth are often removed due to a lack of space due to us evolving smaller jaws due to our food being cooked.
Pigs as Omnivores
You'll notice from the image of the pig skull that they also have
Incisors - to cut
Canines - to stab and tear
Molars - to crush and chew
Cats and Dogs as Carnivores
Looking in a Cats mouth we see the mouth of a Carnivore (meat eater)
Carnivores have very large Canines - this is because they use their Canines to stab and grab their prey
Carnivores use their canines as a weapon, and use them in their hunting, watch the lioness stab the warthog with her huge canines
The carnivores incisors are shaped in a more pointy array, like tiny knives slicing into the meat. having more of a point to increase pressure, a pressure point, for ease of slicing.
You can see that their molars are sharp rather than flat.
This is because they use their molars to slice meat off bones and to cut through cartilage and to cut through bones - like butchers knives
Their molars are called Carnassials
Carnivores don't chew for as long as we do. As soon as the meat is small enough to swallow, they do.
They don't chew for as long because they don't need to mix any enzymes in with their food - they don't produce salivary amylase!
They do chew, just not as long as we do - watch a dog or a cat eat - its bite bite swallow.
Herbivores - Rabbits and Cows
Watching the rabbit eat you will see that it bits with its Incisors
It then flips the food back and chews it till it becomes a bolus
Rabbit skull - Molars and incisors, top and bottom
If you look at the rabbits skull you see that it has Incisors for cutting its food and then Molars (and premolars) for chewing
They have 2 Incisors on the top and 10 molars
They have 2 Incisors on the mandible and 10 molars
Notice, they Do NOT have canines - why?
Watching the cow eat, you will see that it tends to rip the grass
It then flips the grass to the back of its mouth and chews it with its molars
You can see on the cow skull that it has a big space where other animals would have their canines - so no canines
You'll see that they have more and bigger molars than we do - a total of 24 molars
The most interesting thing is that they have 8 Incisors and these are all on their mandible (lower jaw)
They have no incisors on their maxilla!! That is No Incisors up top
So when Cows bite the grass, the grass becomes trapped between their incisors and the bony pad where other animals would have incisors, this is called a Dental Pad.
So Cows will use their incisors, dental pad and their tongue to hold grass in place, and will then pull the grass thus ripping it
It is thought that this process has evolved to allow them to get to shorter bits of plant material than other animals.
Animals that have this dental pad include cows, sheep, deer and goats. These animals are known as Ruminants - they have an extra part to their digestive system called a ruminant - more on this later.
Deer skull - look no canines and no top incisors!
Goat skull - Molars only on the top. Molars and incisors on the bottom
Horses and other things
Have a look at the horses skull
It does have 2 sets of Incisors
Top incisors and bottom incisors
Maxilla Incisors and Mandibular Incisors
But why?
This is because horses are NOT ruminants. So they have to chew their food more thoroughly than cows, but - more about this later :-)
Other interesting things are that most tusks are canines. For instance the tusks of pigs or wild boar.
However elephant tusks are incisors thus they have no other incisors or canines, their only teeth are molars. Think about how they eat
The link to the right has lots of different skulls found in NZ. Have a look, see what teeth do they have and think about what they eat.
The link below has lots of interesting stuff about teeth, skulls and eating
Tooth
The Crown - The seen part
The Neck - The part in the gums
The Root - The part in the jaw
Enamel
The outside layer of the tooth is the strongest substance in the human body - stronger than bone
This is Enamel
It is super strong due to the fact that the teeth grind against each other
The strength comes from the 96% Calcium Phosphate it contains (basically stone)
Enamel is made on the tooth before it 'erupts' or before 'your getting a new tooth'. In other words, the Enamel forms while the tooth is still hidden inside your jaw.
If you don't have your wisdom teeth yet, then it might come up on an x-ray. Meaning it is still in your jaw and it just hasn't 'erupted yet'. While your wisdom tooth is hidden inside your jaw it is getting its enamal
Once the tooth has been erupted, it will no longer get any new Enamel.
So the Enamel on your erupted teeth now, this is all the Enamel it will ever have. No new enamel is made.
It does have one weakness though - Acid
Acid can easily dissolve enamel
Bacteria produce acid as part of anaerobic respiration
This is how cavities are formed. Bacteria will eat the food left over in your mouth. As they do that they release acid. The acid dissolves some of the enamel. The bacteria bury deeper into the tooth. As the bacteria eat, they grow and reproduce. As their numbers increase your breath starts to go bad. You start to create a visible film of bacteria and food at the bottom of the crown where the gum is - this is plaque. As the plaque builds up, the gums can become inflamed and will bleed easier. This can lead to gingivitis (inflammation of the gingiva). Finally, the bacteria start to use some of the calcium in the dissolved enamel to create a protective coat or roof that keeps them safe from you - this is Tartar. Tartar is hard to remove by brushing as it contains calcium. It is the stuff that the dentist removes with the metal scrappy things. Removal of Tartar is very very important, it is one very good reason to see your dentist once a year. If bacteria get to the pulp they will grow very quickly - you'll need a filling to fill up the cavity that they have made and have been living in. Or, if it gets really bad, you'll need your tooth removed - if not the bacteria can start to infect the bone and blood
Dentin
The next layer is the Dentin
Nutrients released from the blood vessels in the pulp, diffuse through the dentin to the cells that create the enamel.
The dentin is not as hard as the enamel, but it is more flexible. This flexibility comes form the dentin have more collagen (like your ears). This allows the tooth to flex rather than chip (it is the Enamel that is usually damaged when you 'chip' a tooth. This usually needs to get capped to stop bacteria from getting into it) .
Dentin contains between 40% and 70% Calcium Phosphate depending on the source of your research.
Dentin continues to be made within teeth though-out your life. Thus preserving the life of the tooth. The dentin is made by odontoblasts.
Pulp
The final part is the Pulp. This area contains the blood vessels and the nerves amongst the cells that make the tooth. These cells are the odontoblasts and odontoclasts. The odontoblasts make Dentin, while the odontoclasts break it back down so it can be remodeled - this stops the dentin from getting too old and accumulating to many microfractures.
The nerves in the pulp are what tells you bit on something solid in your food that you should not eat - like if you are eating some lettuce, but there is a piece of sand in it. The nerve also prevents you from biting too hard on something solid and breaking your tooth.
The blood vessels release nutrients and oxygen for the cells of the pulp, the dentin and the enamel. The blood vessels also take away any waste products as well as any carbon dioxide.
Cementum
To secure the tooth in place, you have Cementum - this is strong connective tissue that anchors the tooth to the jaw. This contains 50/50 Calcium Phosphate and Collagen
Gingiva
The gums are also known as the gingiva.
The part of the tooth in the gingiva is called the Neck
Saliva
Saliva is 99% water
It also contains some mucus - this is why a vial of spit looks different from a vial of water
It contains some antimicrobial enzymes
It contains alpha amylase
It contains lipase that is mixed with the food but is not activated until the food arrives in the stomach
Saliva serves 3 purposes:
To provide is to provide a fluid medium so that chemical reactants such as enzymes can float around and to provide space between nutrients for enzymes to get in
Through this fluid medium flavors can float to the taste buds
To act as a lubricant for the swallowing process
Keep the oral cavity moist - and moisten any air entering through the cavity
It has antimicrobial agents. These are found in all animals (naturally some microbes have evolved defenses to this). This antimicrobial effect is especially important for animals that lick their wounds like dogs. (however, it is not as effective as human made antibiotics which is why dogs will often need a cone collar after surgery)
As the food is chewed saliva is mixed throughout. The end product is the bolus - a chewed ball of food and saliva.
Amylase
Carbohydrates
Photosynthetic organisms make glucose, they then stick glucose to other glucoses to make more complex structures. One of the reasons for this is that glucose is surrounded by water, it is soluble. If you stick glucoses close to each other, then the space for water reduces. This makes it easier to store glucose. As this continues, and more water is excluded, the complex structure becomes insoluble.
Another reason plants do this, is that complexes of glucose are used in their structure - cellulose makes up the cell wall of plants - this is made of glucose. Even wood is mostly glucose molecules. This complex is too hard for us to digest, but bacteria and fungi can through their extracellular amylase and other similar enzymes.
Photosynthesis is the process of combining water and carbon dioxide, to make glucose. Because of this glucose and complexes of glucose are called Carbohydrates - Carbo = Carbon. Hydrate = Water (get hydrated).
Single glucose molecules don't exist for long as they are quickly joined up with other glucose molecules. Dimers are two glucose molecules, these are called disaccharides. Monomers of one glucose are called monosaccharides. (Mono = monobrow = one)
Monomers and Dimers of two glucose molecules are called, simple sugars or simple carbohydrates. These include; Maltose, Fructose, Sucrose and Lactose
'Poly' means many - like Polynesia = many islands. Polymers of glucose contain many glucose molecules. polymers of glucose are called polysaccharides.
Polysaccharides are also called Complex sugars or Complex Carbohydrates. These include Starch (that we can eat) and Cellulose (Fiber). Furthermore, insects stick glucose molecules together to make their hard exoskeleton - chitin. And animals like us store sugar in our muscles and liver as Glycogen
The world is made out of sugar
The world is sweet as!
Amylase is an enzyme found throughout all of the domains of life. Bacteria and Archaea excrete it to digestion carbohydrates in their environment, as do Fungi. Plants use it to digest their own Starch stores. Animals use it to digest carbohydrates. All of these organisms are doing the same thing: turning complexes of sugar into just glucose.
This happens because the complexes can't be used for cellular respiration
Cellular respiration, both aerobic and anaerobic, uses glucose
Aerobic cellular respiration is: 1 Glucose + 6 Oxygen = Carbon dioxide + Water
But for cellular respiration to occur, the glucose needs to get into the cells
For this to happen we have:
Ingestion - putting food into your mouth
Digestion - breaking the food from big insoluble bits into soluble bits
Absorption - taking the food into the blood stream
Assimilation - glucose and nutrients moving from the blood into the cells
Amylase is a carboxylase - carboxylases are enzymes that digest carbohydrates.
There are others, including glucosidase.
Glucosidase (also known as glucoamylase) will cut the disaccharide Maltose into two glucose molecules.
And Sucrase. Sucrase cuts the disaccharide Sucrose (Glucose + Fructose) into glucose and fructose (fructose is also C6H12O6 - so its basically the same as glucose except it makes a pentagon shape rather than a hexagon shape.
Importantly, only Amylase is in the Saliva.
The other carboxylases are in the Small Intestine
Amylase works by binding to a glucose and adding a water to that joint. It splits the water, adding Hydrogen to one glucose and the other 2 atoms, oxygen and a hydrogen (hydroxide, -OH) to the other side.
It continues this process over and over again. Chopping at the carbohydrate like you turning a tree into fire wood. Cutting and cutting and cutting until it is tiny and can go into the fireplace / cell.
Amylase is produced by the pancreas in all mammals
In humans we also get amylase in our saliva. In fact 30% of the digestion of carbohydrates occurs in your mouth.
Humans have this amylase in our saliva, because as a species, starch is the biggest part of our diet. It is such for all cultures: Rice, potato, taro, kumara. Along with flour products, pasta and bread.
In fact 30% of starch digestion occurs in the mouth
pH of the Mouth vs Amylase activity
Have a look at the graph
It shows the level of activity of starch (its ability to hydrolyze of split starch) for various pH values.
As you can see Amylase is most active around a neutral pH
The amylase that is in the mouth has only a short window to get this digestion done. As soon as it is in the stomach it is denatured and thus stops working.
Alpha amylase has an optimum pH of between 6.5 and 7. So this is pretty much neutral, with a hint of acidity.
However, amylase is denatured in low, acidic pH's as well as in very high pH. Once this happens the amylase will no longer function.
Temperature of the Mouth vs Amylase activity
Have a look at this graph.
It shows the level of activity for amylase as a function of temperature.
You can see that amylase is most active near human body temperature = 37.5 C
If the enzyme is cold, the reaction occurs slower
If the enzyme is too hot, it will denature and stop working
If the pH is too acidic or too basic, then the enzyme will denature
pH and temperature regularly feature as exam questions. Have a watch of the clips in this section to ensure that you can confidently talk about:
enzyme activity
optimum temperature
pH
rate of reaction
substrate
reactants
collision
orientation
energy
Catalyst (Enzymes are catalysts!)
Amylase and Evolution
Have a look at the image above.
Here we have number of copies of the amylase gene - including both salivary and pancreatic.
The animals with the highest levels are Humans, Mice, Rats, Pigs and Dogs.
Three of these are Omnivores, and one is a carnivore. However, and this is important, there are NO Herbivores!
Dogs only have trace amounts of amylase in their saliva (roughly 1 unit for each of the 1000 units that humans have). But this is a lot more than wolves (roughly 1 unit for every 20,000 human units).
None the less, dogs (C. lupus dom.) and wolves (C. lupus) are closely related. Yet their is a massive difference in the copies of the amylase gene - why would this be? Could it be to do with them living with humans and scavenging from our left-overs?
Here Blue represents sugars and Yellow is starch
Omnivores that eat tubers in roots like humans and pigs have a large amount of amylase.
This is because plants will often store glucose as starch in their tubers so that they can survive winter
The green parts of plants will usually contain sugar, as this is being use for cellular respiration. This sugar is often also pushed into fruits, so that animals will eat the fruits and the seeds inside of the fruits and will then drop the seeds in their feces. The movement of sugars will often occur in the stems of plants - this has been used by humans in sugar cane and in maple syrup.
Interestingly herbivores that eat grass have either only a little bit of amylase or none. Cows and sheep have no amylase in their saliva. This is because grasses are not high in starch!! Rather, they are high in cellulose (fiber) (that is broken down by bacteria) and sugar!
In fact feeing some herbivores starchy foods can make them sick
Starch is a polysaccharide that is (generally) digested by the enzyme amylase to glucose in the small intestine of Horses. Starch increases blood glucose and insulin concentrations.
Above is a graph analyzing what is in grass at different times of the year.
The Brown line is the Total amount of non-fiber carbohydrates - everything else is Fiber
The Red line is for glucose and fructose - monosaccharides
The purple line is for disaccharides (sucrose) and a polysaccharide called Fructan - this can only be digested by gut bacteria
The Yellow line is the amount of Starch
Looking at this graph, what implications does it have for the need for salivary amylase in the animals that eat grass?
Indeed, the herbivores like horses, cows, sheep, goats and deer - do NOT have salivary amylase!
This image shows the Starch content of common flours and flour products.
How much of this do you eat? How much would make up a typical meal for you?
Below is the % of starch and sugar in Rice.
It also shows the % of starch and sugar in two Indonesian dishes made from the Yam variant of sweet potato
Potatoes are a big daily food source for many human cultures. How many potatoes based meals do you think you eat in a day?
How many different things can you list that are made with potatoes?
Below is a graph that shows the starch, fiber and sugar content for two common potato variants: Sweet Potato and White Potato.
Could their be a relationship between the presence of Salivary Amylase in humans and our consumption of potatoes and other plant tubers, our consumption of rice and our consumption of wheats and grains????
Have a look at the image.
Here we see the number of copies of the amylase gene in different populations around the world. They bars are colour coded for high-starch diet and low-starch diet.
What does it tell you?
Below we have an image that shows the quantity of Salivary amylase and the diets of our closest non-human relatives
These are our ancestors, our closest non-human relatives
The graph shows the level of Salivary Amylase.
Each line on the graph is a factor of 10. So: 1, 10, 100, 1000
Our closest relative, the chimpanzee has roughly 80 units per milligram of saliva. Whereas humans have 800 units per mg of saliva.
What does this tell you? Think of diet and evolution. Then watch the Sci Show clip after doing the thinking thing :-)
The final image for this section is very informative
Here we look at a range of species, their level of salivary amylase and their number of copies of the gene for salivary amylase
Take careful note of the axis, they are on a log scale, which means that each line is 10 times more than the previous line
I have left the caption under the image, and the link to the original article. The caption makes for interesting reading
What does all of this mean in terms of Salivary amylase and diet?
(a) Representative starch lysis plate assay showing the extent of lysis caused by the enzymatic activity of amylase in the saliva of various mammalian species. The left panel shows side-by-side comparisons of domesticated species and their counterparts in the wild. The agar plate shows the lysis caused by representative primate saliva samples.
(b) Density plots showing salivary amylase activity in different species as measured by a high-sensitivity colorimetric assay. The dotted line represents the mean amylase activity level determined in the serum of humans, rats, pigs, boars, and gorilla
(c) Scatter plot of amylase activity and gene copy number in multiple species. The dotted line represents the same serum activity shown in (b). Images of starch plate lysis caused by standard dilutions of amylase are shown to the left of the y-axis next to their corresponding activity values.
Salivary Glands
The roughly 1 liter of saliva that you make each day is made in the salivary glands
In these diagrams we can see 3 pairs of salivary glands (so 6 all up). They have been highlighted blue
Parotid Gland
The gland just under the skin of your cheek, but on top of the muscle, is called the Parotid Gland. This is the largest salivary gland. This produces the most saliva once stimulated, over 50% of total saliva once eating, but not when not stimulates
This releases a flow of saliva into your mouth next to your upper second molar, between your cheek and your gums.
There are two Parotid glands; one on each side of the mouth (right and left)
Submandibular Gland
Directly underneath the back of your jaw, on the inside, is the Submandibular gland (of which there are two; right and left).
Sometimes you can feel them, near the hinges of your jaw
The submandibular gland drains into the Wharton's duct. This is also known as the Submandibular duct. You can see these ducts when you lift up your tongue in the mirror. You will see the two little holes under your tongue
The Submandibular gland provides 70% of your saliva when not eating. Once you smell food, the parotid gland becomes stimulated and increases it production, overtaking the submandibular gland as the main producer of saliva.
Sublingual Gland
In the soft bit directly behind your chin is where your Sublingual gland sits. The sublingual glands are the smallest This drains under your tongue, from the back to the front, through the sublingual ducts (also known as the ducts of Rivinus).
The pair of sublingual glands are the smallest salivary glands and product only 5% of total saliva
The Wharton's duct (submandibular duct's) in action
