KS3
Nutrition & Digestion
Nutrition is a 3-part process involving consuming, digesting and excreting food and drink.Â
It is vital for maintaining a healthy lifestyle.Â
The digestive system
Food travels from the mouth to the anus through a system called the digestive system. The digestive system comprises of many organs of which food passes through the majority.
From the mouth
In the mouth, teeth break down food through a mechanical process.
Enzymes found in saliva are used to break down food through a chemical process.
These enzymes break down fats and carbohydrates. Saliva is mixed with the food. Saliva is also used to lubricate food to help with passage down the oesophagus.
Down the oesophagus
The Oesophagus is a thin pipe that simply links the mouth to the stomach.
The oesophagus (along with the small and large intestine) pushes food along using muscles found in its lining, this process is called peristalsis.
To the stomach
The stomach is a muscular hollow organ. This is where food already broken down by the mouth gets churned up (mechanical process) with stomach acid (chemical process).
Stomach acid is made up of hydrochloric acid, this not only helps to break the food down further but also kills bacteria.
Next the small intestine
After the stomach is the small intestine. The small intestine is where all the nutrients from the food is absorbed straight into the blood.
Lipids (fats and oils), carbohydrates and proteins are broken down here.
The small intestine is made up of specialised cells called villi. Their role is to increase the surface area of the small intestine so that as much nutrients etc can be absorbed.
In a square millimetre there is around 10 to 40 villi and the small intestine is about 20 feet long with a diameter of 2.5cm, so this gives it a huge surface area.
Help from the pancreas
The pancreas is attached to the small intestine and produces the enzymes that break down the lipids (fats and oils), carbohydrates and proteins.
The liver joins in
The Liver is also attached to the small intestine and produces a substance called bile. Lipids are large molecules that need to be broken into smaller molecules through a process called emulsification.
Bile doesn't digest the lipids, it simply makes lipids smaller which increases the surface area for the enzymes to then break down.
That if your stomach is empty and you are ill, you can sometimes vomit up bile. It is yellow in colour but should be no cause for concern.
Onto the large intestine
After the small intestine is the large intestine. The large intestine is where water is absorbed and any food that couldn't be broken down continues to move along.
The digestive system cannot break fibre down. Fibre is used to help the digestive system and helps prevents constipation.Â
Arriving at the rectum
The rectum is after the large intestine and this is where all the food that wasn't broken down/ waste from the body is stored as faeces.Â
Time for the toilet!
Faeces then passes out of the anus and this ends the digestive system.
What is an enzyme?
An enzyme is a biological catalyst. A catalyst is something that speeds up the rate of reaction but remains unchanged, which allows it to be used repeatedly time and time again.
Enzymes are protein molecules that are categorised into 2 types. Then first type break down large molecules and an example of this would be digestive enzymes, the second type synthesise (build) large molecules.
The lock and key model
Enzymes have what is called an activation site this is the part that binds to a substrate. A substrate is a specific substance that only a specific enzyme can break down. It is much like only a certain key can open a certain door. This process is called the lock and key model.
How do we name enzymes?
So we can give names to each of these enzymes linked to the substrate that they break down.
Carbohydrase
Carbohydrase breaks down carbohydrates, and is located in the mouth, small intestine and pancreas.
Protease
Protease breaks down proteins, they are located in the stomach, small intestine and pancreas.
Lipase
Lipase breaks down lipids and is located in the small intestine and pancreas.
What affects do enzymes have?
Food can only be absorbed in the small intestine. Nutrients must be small enough to diffuse through the lining of the small intestine to get to the bloodstream.
The large molecules will not pass through the lining until broken down. When these nutrients reach their target enzymes can break down or synthesise the required substance.
If the large molecules are not broken they pass through the large intestine and become faeces in the rectum.
Can enzymes stop working?
Enzymes are never affected by the chemical reaction they just speed it up, this is why they are able to be used time and time again.
Enzymes however can be affected by temperature or pH. Each enzyme works in an environment that has a specific temperature and pH, so if it moves out of this threshold it can change shape. When an enzyme changes shape it is called denaturing.
This means the activation site would not be able to bind to the substrate and so the enzyme won't work anymore, which slows the rate of reaction down.
Nutrition and a healthy diet
To be a healthy individual it is important that you have a well-balanced diet. The main types of nutrients your body needs are carbohydrates, protein, lipids (fats and oils), vitamins and minerals. Making sure to eat a balanced diet is important because too much of one thing and you can gain mass or too little and you could lose too much mass.
Protein
All cells in the human body contain some protein, which is why it is necessary to add to our diet.
Protein, is used by the body for growing and repairing cells. Proteins are compounds made of amino acids. Your body connects amino acids to create the new protein it requires.
You can find protein in meat, fish and dairy products.
Fibre
Fibre is a complex carbohydrate and doesn't raise blood sugar levels. The body breaks down carbohydrates into glucose but it is unable to digest fibre, so it passes through undigested.
Sometimes it is called roughage and it needs to be eaten. Fibre is valuable to the digestive system as it helps to pass through the food we eat helping prevent constipation. There are two different types of fibre.
Soluble fibre
This type of fibre is able to be dissolved in water. You can find this type of fibre in oats, peas, apples, carrots and barley.
Soluble fibre transforms into a gel-like substance when it enters the intestines and gets digested by bacteria in the large intestines.
Some good bacteria in the gut feed of this kind of fibre.
Insoluble fibre
Insoluble fibre is unable to be dissolved in water. Some of the best sources of insoluble fibre are nuts, cauliflower, wheat bran and potatoes.
Insoluble fibre will remain mostly unchanged because it is unable to be digested. Its benefits include reducing the likelihood of becoming constipated and may even reduce the risk of colorectal cancer.
The benefits of Vitamin A are healthy skin and hair, the prevention of upper respiratory infections and fertility issues.
Vitamin A is vital for vision and growth. We can find it in fatty fish, organ meats like liver, milk, cheese and eggs. We can also find it in orange fruits and vegetables like carrots, sweet potatoes, apricots, mango and pumpkin.Â
Vitamin B1 or thiamin is a vitamin that helps the body to use carbohydrates as energy. This vitamin is plays a vital part in maintaining healthy heart function.
Lots of B1 can be found in beef, pork, yeast, nuts and pulses as well as vegetables.Â
Riboflavin or vitamin B2 is one of several B vitamins that are vital for humans eye, skin and nervous system health.Â
Vitamin B2 dissolves in water and so is passed through the bloodstream. The body is only able to store small amounts so we need a daily intake of B2.Â
We can take B2 in supplement form or we can find B2 in fish, meats and vegetables. Avocados, peas, pumpkins and yeast extract all contain B2.Â
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Brain function, red blood cell production and nerve tissue health are looked after by vitamin B12.Â
Its is an important vitamin for the body and the benefits are just as important. Vitamin B12 aids your ability to think, helps to create and regulate DNA and is necessary for the production of energy from food.Â
You can get vitamin B12 from meat, fish and dairy products like milk, cheese and eggs.Â
Vitamin C is a vital vitamin to maintain healthy bones, blood vessels and skin.Â
Its an antioxidant and comes in supplement form as well as being present in fruits and vegetables.Â
Vitamin C is needed by our bodies daily to help with the absorption of iron and to boost the immune system.Â
We can take vitamin D supplements, but we can also spend time in the sunshine which is how the body naturally produces vitamin D.Â
Although it is called vitamin D, it’s actually a hormone linked with calcium absorption.Â
A deficiency in vitamin D can cause rickets in children, which is a softening of the bones. This leads to a bowlegged appearance.Â
You can get vitamin E from food and supplements. It has natural antioxidant effects and could help with hair shine and condition. You can find it in nuts and seeds, breakfast cereals and vegetable oil.Â
We need vitamin K to help with blood clotting and wound healing. Vitamin K1 comes from plants and K2 occurs in a few fermented foods and in some animal-based foods.Â
How do vitamins and minerals fit into nutrition?
Minerals like Calcium, Iodine, Iron and Zinc play a vital role in the body, from making red blood cells to keeping our bones strong and muscles healthy.
Vitamins play an equally vital role in our health. They help us to grow, fight infections and function.
We all need the same vitamins and minerals but the amount we need depends on your age and sex.
Carbohydrates
Carbohydrates give our body the main source of energy it needs. We can find carbohydrates in plants and dairy like milk.
Milk contains lactose which is a form of carbohydrate.
We can find carbohydrates in fibre such as nuts, seeds and whole grains. Sugars that occur naturally and the sugars we add to baking and desserts.
Finally they occur in sugar alcohols. The body does not fully absorb these sugars. They are found in chewing gum, baked goods and sweets in the form of sweeteners.
Starch
Starch is a complex carbohydrate. Fruits and vegetables store starch as energy.
Starch releases energy more slowly due to it being harder to break down. When you hear the word starch it usually brings the image of potatoes or rice and pasta to your mind.
Starchy vegetables like potatoes are great at thickening dishes like soups, making them very handy for cooking.
Consisting of glucose molecules, starch is a long chain molecule.
Malnutrition
Malnutrition occurs when the body doesn't receive the nutrition it needs from its diet.
There are several causes of malnutrition, not being able to access food due to income, mental and physical health issues and poor nutrition choices.
Malnutrition causes weight loss, and slow or delayed growth and it can also be life-threatening. There is the risk of infection and slow wound healing and a range of health issues.
There are three types of malnutrition, waisting, stunting and obesity.
Obesity
If a person has a high body mass index (BMI) meaning they have excess weight or body fat they may be obese.
Obesity can cause a range of health conditions that can be serious. Type 2 diabetes, cardiovascular disease and high blood pressure can be the result of obesity.
When you consume more calories than your body can use as energy, the excess will be stored as fat. Consuming food items and drinks that are high in sugar content will add to the risk of weight gain.
BMI
Your body mass index (BMI) measures your mass and height, then calculates a persons BMI helping explain if you are underweight, normal, overweight or obese.
BMI = Mass (kg) / height2 (M2)
BMI = less than 18.5 then your underweight.
BMI = 18.5-24.9 then your normal (healthy).
BMI = 25.0-29.9 then your overweight.
BMI = Greater than 30.0 means your obese.
Diet choices
It isn't just poor diet choices that lead to obesity, sometimes genetics can lead to the risk of obesity.
The best way to avoid obesity is to eat a varied diet that's full of a range of fresh foods and fibre to aid digestion.
Making sure to incorporate movement into our daily lives is important. It's not just going to the gym that counts. Jobs around the house, walking, and physical work can all help towards this.
What is poo?
Poo is also known as faeces or stool. It is the undigested waste product of the body.
Poop comes in different shapes, sizes, colours and smells!
Each has different meanings and indications of what might be happening with your health.
What is poo made up of?
The waste products in your poop can include water, bacteria, bile and fibre. Whatever your body cannot digest and break down will be passed through your poo.
Lots of factors can affect the shape and texture of your poo, including water intake, imbalance of gut bacterial and some infections that can cause diarrhoea.
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