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- Identify the types of human teeth (incisors, canines, premolars and molars)
The following diagram has everything you need to know:
The above diagram has more detail than you need to know – just learn where the incisors, canines, premolars and molars are, and what they look like.
Note: the bottom edge of incisors are usually flat, while the bottom edge of canines are pointy.
- Describe the structure of human teeth, limited to enamel, dentine, pulp, nerves and cement, as well as the gums
Enamel: Hard outer layer of the crown. The hardest substance in the body.
Dentine: not as hard as enamel. It forms the bulk of the tooth. If there are gaps in the enamel that expose the dentine to the outside, or enamel is very thin, your teeth will be sensitive.
Pulp: soft tissue, contains blood capillaries and nerve supply to the tooth.
Cementum: also known as cement. The layer of bone-like tissue covering the root. Not as hard as enamel.
Gums: soft tissue that immediately surrounds the teeth and bone. Protects the bone and roots of the teeth, provides an easily lubricated surface.
- Describe the functions of the types of human teeth in mechanical digestion of food
Incisors are sharp and are used for cutting food into small chewable pieces.
Canines are at corners, and are even sharper – they’re also used to bite into and tear food.
Premolars: These have a flat surface, and are used to chew and grind food.
Molars serve the same purpose as premolars and also have flat surfaces.
- Describe the proper care of teeth in terms of diet and regular brushing
Brush your teeth twice a day with fluoride toothpaste and floss your teeth daily – fluoride helps protect your teeth, and brushing and flossing your teeth prevents the build-up of food particles and plaque.
Visit your dentist at least once every 6 months.
Eat a well-balanced diet – eating food with high sugar and carbohydrate content can cause dental decay.
Don’t smoke – smoking or using spit (smokeless) tobacco can lead to dental decay.
Eating calcium and vitamin C rich foods can also promote the health of your teeth – Vitamin C increases the absorption of calcium, and calcium strengthens your teeth. Vitamin C also keeps your gums strong – lack of vitamin C can lead to weak gums, which can cause your teeth to come loose, your gums to bleed, etc.
- State the causes of dental decay in terms of a coating of bacteria and food on teeth, the bacteria respiring sugars in the food, producing acid which dissolves the enamel and dentine.
Bacteria tend to colonise around any leftover food particles in your teeth. They respire the sugars in the food and produce an acid as a result of that respiration. This acid dissolves your enamel, forming small holes called cavities. Once those holes grow deep enough to reach your dentine, the acid dissolves the dentine too.
These cavities bring the outside of the tooth closer to the nerves in the pulp. The acid irritates the nerve endings on those nerves, causing a toothache.
Eventually, the bacteria will get into the pulp cavity and create a painful abscess in the root. Often, the only way to treat the abscess is to pull out the tooth. To prevent the cavity from progressing this far, dentists must clean and fill the cavity.
Eating high sugar foods (like cake, biscuit, drinking fizzy drinks, etc.), especially at frequent intervals, will increase the likelihood of dental decay – so eat sugary foods less often.
Poor teeth brushing habits, like forgetting to brush your teeth twice a day or brushing your teeth with bad technique means that sugar particles may be left in your teeth. This again increases the likelihood of dental decay. Note: brushing your teeth is more important in preventing gum disease than removing bacteria – it doesn’t do much in the way of eliminating bacteria. However, the fluoride in fluoride toothpaste kills bacteria and increases the resistance of your teeth to dental decay.
Flossing also helps remove food particles from between your teeth and helps protect against gum disease.
Having a check-up with your dentist every six months means that any dental issues can get treated at an early stage.
- State the significance of chemical digestion in the alimentary canal in producing small, soluble molecules that can be absorbed.
Food molecules must be small soluble to be absorbed.
Ultimately, it is mainly the chemical properties of a molecule that determine whether or not it is water-soluble. Mechanical digestion can help break up large clumps of food but does not alter the chemical structure of the food. Chemical digestion, however, breaks up large food molecules like fats and starch, into smaller food molecules like fatty acids, glycerol, sugars, etc.
It converts large insoluble molecules into small, soluble molecules that can be absorbed, using enzymes.
- State the functions of enzymes as follows:
- Amylase breaks down starch to simpler sugars
Amylase is an enzyme that breaks up the bonds between the sugar monomers in starch. As a result, you get simpler sugars like glucose.
- Protease breaks down protein to amino acids
Protease enzymes break the ‘peptide bonds’ that hold amino acids together. This gives you smaller peptides and amino acids.
- Lipase breaks down fats to fatty acids and glycerol
Lipase breaks down the ‘ester bonds’ holding the fatty acids and glycerol in a fat molecule together. Note: most fats are triglycerides (glycerol bonded to three fatty acids), so may also be referred to as a triglyceride.
- State where, in the alimentary canal, amylase, protease and lipase are secreted.
Amylase: from salivary glands into the mouth, and from the pancreas into the duodenum.
Protease: the stomach and the pancreas.
- State the functions of the hydrochloric acid in gastric juice, limited to killing bacteria in food and giving an acid pH for enzymes
Hydrochloric acid makes the stomach contents very acidic. This kills any bacteria that manage to enter the stomach.
The low pH maintained by hydrochloric acid is also the optimum pH of the protease enzyme. This means the enzyme can efficiently break down proteins.
- Explain the functions of the hydrochloric acid in gastric juice, limited to the low pH:
- Denaturing enzymes in harmful microorganisms in food
- Giving the optimum pH for protease activity
Certain specialised cells in the stomach wall secrete hydrochloric acid. The hydrochloric acid maintains the stomach contents at a pH of 2.
This low pH denatures any proteins in the stomach (by breaking the specific bonds that hold the protein in shape), including enzymes that belong to harmful microorganisms that may have entered the stomach. This prevents those microbes (microbe is short for microorganism) from carrying out any reactions, stopping them from doing anything harmful.
The optimum pH of the protease enzymes secreted into the stomach is pH 2, so maintaining the stomach at a low pH helps protease enzymes function more efficiently.
Note: not all protease enzymes have an optimum pH of 2.
- Outline the role of bile in neutralising the acidic mixture of food and gastric juices entering the duodenum from the stomach, to provide a suitable pH for enzyme action.
Bile is alkaline in nature. This helps neutralise the acids in the gastric juice and food that enter the duodenum.
Enzymes secreted from the pancreas and in the small intestine have an optimum pH that is slightly alkaline or neutral (pH 7 and up). The neutralisation of the acids helps provide the enzymes with an environment with a pH closer to their optimum pH. This allows enzymes to function more efficiently.
- Outline the role of bile in emulsifying fats to increase surface area for the chemical digestion of fat to fatty acids and glycerol by lipase
Bile contains something called bile salts. Bile salts may also be called bile acids or bile pigments.
These emulsify fats, which increases their surface area. I found a nice definition of emulsification at Medical Dictionary:
“The breakdown of large fat globules in the intestine into smaller, uniformly distributed particles, largely accomplished through the action of bile acids, which lower surface tension.”
Since the emulsified fats have a larger surface area, there is more surface for the enzyme lipase to act on.
Lipase breaks up the fats into fatty acids and glycerol, making them suitable for absorption.
- Explain the significance of villi in increasing the internal surface area of the small intestine.
Villi (singular: villus) are in-foldings or finger-like projections in the internal intestinal wall. These villi are covered in microvilli which are further finger-like projections, as shown in the diagram.
Note that a lacteal is basically just a small lymphatic vessel.
These “infoldings” significantly increase the surface area of the small intestine, so nutrient molecules can diffuse into the blood or lymph faster!
- Describe the structure of a villus.
This has already been done in the previous learning objective!
- Describe the roles of capillaries and lacteals in villi
Broken down nutrients are transported across the intestine wall into the capillaries and lacteals. These nutrients are then transported to other parts of the body, where they can be assimilated.
Primarily, glucose and amino acids are transported into the capillaries and lipids (fats) are transported into the lacteals.
Notes submitted by Sarah
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