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- State what is meant by the term balanced diet and describe a balanced diet related to the age, sex and activity of an individual.
A balanced diet is a diet consisting of the right proportions of every type of nutrient (carbohydrates, proteins, fats, vitamins, minerals, etc.) in suitably sized portions.
A balanced diet should contain carbohydrate, fat, protein, fibre, vitamins, minerals and water. Note that fibre cannot be digested: it used to form “roughage” in the intestines, so the intestine walls have something to push against when moving the food along the alimentary canal.
A balanced diet for different people are slightly different, because our energy requirements differ from person to person.
Note that the energy needed is provided by our carbohydrate and fat intake.
Males usually use more energy than females, and we tend to use more and more energy as we age – until we stop growing, that is.
Growing children need a higher proportion of protein than adults do and pregnant woman require extra nutrients for the development of the foetus.
- Describe the effects of malnutrition in relation to starvation, coronary heart disease, constipation and obesity.
Malnutrition occurs when you don’t have a balanced diet. The definition I found online states that malnutrition is “lack of proper nutrition, caused by not having enough to eat, not eating enough of the right things, or being unable to use the food that one does eat.” (You don’t have to learn this definition!)
Starvation is caused by consuming too little food (maybe due to lack of food supply or a mental disorder causing an intense fear of gaining weight). This leads to intense weight loss, organ damage and in serious cases, death.
Coronary heart disease (CHD) is when cholesterol sticks to the walls of your arteries. Sometimes, this even forms blood clots. This cuts off or limits the supply of blood that your heart muscles receive, leading to a heart attack. This arises from consuming too many saturated fats.
Constipation is when you are unable to defecate – which can be extremely painful. This is caused by a lack of fibre – your intestines won’t have anything to push on in order to move the food along the alimentary canal if there’s no fibre.
Obesity arises from consuming too much food. This can lead to several diseases such as diabetes, strokes, difficulty breathing, etc.
- Define ingestion as taking substances (e.g. food, drink) into the body through the mouth.
That point’s pretty self-explanatory.
- Define egestion as passing out of food that has not been digested, as faeces, through the anus.
This point doesn’t really need an explanation, either!
- Identify the main regions of the alimentary canal and associated organs, including mouth, salivary glands, oesophagus, stomach, small intestine: duodenum and ileum, pancreas, liver, gall bladder, large intestine: colon and rectum, anus.
This diagram should explain it all:
- Describe the functions of the alimentary canal as listed above, in relation to ingestion, digestion, absorption, assimilation and egestion of food.
First, let’s break down the movement of food through the alimentary canal:
- Small intestine:
- First the duodenum
- Then the ileum
- Large intestine:
Ingestion is the taking in of food
Digestion is the breakdown of food molecules.
Absorption is when the broken down nutrient molecules are absorbed into the blood or lymph through the gut wall.
Egestion is the removal of undigested substances from the alimentary canal, usually through the anus.
Now let’s go through the function of each organ!
Note that there are two types of digestion – Chemical digestion (involving enzymes) and Mechanical digestion (involving the physical crushing of food).
The mouth contains saliva, which is secreted from the salivary glands. Saliva contains salivary amylase – an enzyme that breaks down carbohydrates (chemical digestion). The mouth also contains teeth, that cut, chew and grind food (mechanical digestion). Food is formed into a bolus, which is then swallowed.
The mouth is used for ingestion and digestion.
The swallowing of food causes it to move from the mouth to the stomach through the oesophagus, by peristalsis.
I found a nice definition of peristalsis online, which I’ll put here:
the involuntary constriction and relaxation of the muscles of the intestine or another canal, creating wave-like movements which push the contents of the canal forward.
The stomach is an organ containing gastric juices (mainly hydrochloric acid and protease enzymes). The acidity (pH2) kills bacteria and the proteases digest proteins. The stomach also churns the food in it. Only digestion occurs in the stomach.
The Pancreas and the gall bladder are connected to the duodenum by ducts. Pancreatic juices and bile (stored in gall bladder) are transported to the duodenum via these ducts. Pancreatic juices contain proteases, lipases (fat digesting enzymes), amylases and sodium hydrogencarbonate (which neutralises the acid from the stomach).
Bile, produced by the liver and stored in the gall bladder, contains bile acids, also known as bile salts – which emulsify fats.
Therefore, the duodenum is a site of digestion.
Secretes pancreatic juices to the duodenum.
As the pancreas uses nutrient molecules to do this, this can be considered a site of assimilation.
Stores bile which is produced by the liver, and secretes it to the duodenum.
The epithelial lining of the Ilium secretes yet more enzymes which breakdown maltose and peptides. The ileum has a huge surface area due to the villi present, allowing a greater amount to be absorbed at a time. The ileum is a site of both digestion and absorption.
The large intestine:
The main function of the colon is to reabsorb the water from the undigested food.
The rectum stores faeces until it is egested.
The anus is the site of egestion – it has sphincter muscles that control when faeces is egested from the body.
- Define digestion as the breakdown of large, insoluble food molecules into small, water-soluble molecules using mechanical and chemical processes.
Say hello to another self-explanatory point!
- Identify the types of human teeth and describe their structure and functions.
Here’s a diagram:
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.
- State the causes of dental decay and describe the proper care of teeth.
Causes of dental decay include:
Not brushing and flossing regularly.
Eating foods with high sugar and carbohydrate content.
Not getting enough fluoride.
Not having enough saliva.
Smoking or using spit (smokeless) tobacco.
To prevent dental decay:
Brush your teeth twice a day with fluoride toothpaste and floss your teeth daily.
Visit your dentist at least once every 6 months.
Eat a well-balanced diet.
- State the significance of chemical digestion in the alimentary canal in producing small, soluble molecules that can be absorbed.
Chemical digestion is the breakdown of larger nutrient molecules into small soluble molecules, usually with the aid of enzymes. It’s only possible to absorb the small water soluble molecules, as only these molecules are able to diffuse into the blood and lymph, across the gut wall.
- Outline the role of bile in emulsifying fats, to increase the surface area for the action of enzymes.
Bile contains bile acids, also known as bile salts, that cause large fat globules to break down into microscopic globules. This increase the amount of fat exposed to the outside (increases the fat surface area), so enzymes have more area to work on and break down the fat.
- State where, in the alimentary canal, amylase, protease and lipase enzymes are secreted.
From salivary glands into the mouth and from the pancreas into the duodenum.
The stomach and the pancreas.
- State the functions of a typical amylase, a protease and a lipase, listing the substrate and end-products.
Acts on the starch in food, breaking it down into smaller carbohydrates. Pancreatic amylase completes this digestion, by breaking down these smaller carbohydrates to their simplest form: glucose.
Substrate – starch and carbohydrates (polysaccharides)
End product – glucose
A general term for any enzyme that breaks down protein molecules into their monomers – amino acids.
Substrate – proteins (or polypeptides)
End product – Amino acids
A general term for any enzyme that breaks down fat molecules (usually triglycerides) into glycerol and fatty acids.
Substrate – fats (triglycerides)
End product – glycerol and fatty acids.
- Define absorption as movement of digested food molecules through the wall of the intestine into the blood.
Yet another self-explanatory point!
- Describe the significance of the 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” greatly increase the surface area of the small intestine, so nutrient molecules can diffuse into the blood or lymph faster!
- Identify the small intestine as the region for the absorption of digested food.
The small intestine is the region where digested nutrient molecules are absorbed into the blood or lymph. Obviously. 😉
- Describe the structure of a villus, including the role of capillaries and lacteals.
The diagram of a villus has already been given above. So has the description, actually!
The only extra features not already mentioned are these:
- The wall of the villi is only one cell thick – decreasing diffusion distance.
- Each villus is approximately 0.5 – 1.6mm in length in humans
- There are digestive enzymes on the surface of the villi
- Villi capillaries take up amino acids and simple sugars, while the villi lacteals take up the fatty acids and glycerol.
- Describe the role of the liver in the metabolism of glucose (glucose glycogen).
After the absorption of glucose from the gut, the glucose is directly transported to the liver via the hepatic portal vein. The liver removes excess blood glucose and stores it as glycogen. This process is stimulated by the hormone insulin.
If blood sugar is too low, then the liver converts glycogen to glucose, so it can be used for respiration. This process is stimulated by the hormone glucagon.
- Describe the role of fat as an energy storage substance.
The number of Carbon – Hydrogen bonds (C-H bonds) in an organic molecule is generally proportional to its chemical potential energy (the energy it can give off when broken down). Fats can have very long fatty acid chains, with hundreds of C-H bonds, so are very high energy molecules. They are harder to break down, however, so are used as a long term energy store.
Fats are usually stored under the skin, and around some organs.
They also serve as good insulators against the cold!
Notes submitted by Sarah.
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