Human Nutrition - Revision Notes - Biology - Aaliya, Naba, Maryam, Zainab
Hello, fellow gobs! Apologies for the inconsistent posting but here is a full briefing of the chapter Human Nutrition.
This post is styled just as notes and so it might not be very fun (unfortunately). This is because we have four days till our biology exams which means we can't spend much time working on this and making it fun...
YET, because I will make sure I do end up providing a better overview later with doodles and very Gobs on a wire type content after our exams finish.
Till then, you can read through and understand.
P.S. the next few posts might be like this too, so watch out!
Happy reading,
7.1 Diet
Naba
Diet is food an animal eats everyday.
There are 6 types of nutrients humans need in their diet:
Carbohydrates
Vitamins
Proteins
Fat
Minerals
Water
A diet must also contain fibre that is not a nutrient and rather just passes through the digestive system and is excreted.
When having all six of these adequately, it is called a balanced diet.
Energy needs:
Humans use up energy and it usually depends on age, sex, and jobs.
Energy comes from foods eaten. If too little is eaten, it may not be possible to obtain enough energy and this can make you tired.
Scientists have calculated the amount of energy in each foods. A gram of fat contains twice as much energy than one gram of protein/carbohydrate.
People’s diets differ according to the age and time of life – A pregnant woman might have to eat more than usual and change the amount of nutrients she takes so that she can help build the baby inside her, and while is breast feeding she has to eat more as well. Similarly, when a person grows old, they start eating lesser due to the decreased rate of their metabolism.
Nutrients Fact File
Food doesn’t only provide energy – it is essential to maintain a balanced diet with all required nutrients for if you don’t, your body would not work properly.
Carbohydrates are nutrients that contain starch and sugar and are required for energy.
Food that contain it: Bread, chickpeas, pasta, sweets, etc
Fats and oils are needed to make cell membranes. When excess, they are stored under the the skin, working as insulators and mechanical protections for organs.
Food that contain it: cooking oil, egg, dairy, butter
Proteins are used for growth and make more proteins such and haemoglobin, insulin, and antibodies.
Food that contain it: meat, eggs fish, peas, beans, nuts
Vitamins are organic substances that are only needed in small amounts and without them, deficiency diseases are caused.
Vitamin C to make protein collagen for the skin, repairs tissue. Without this, scurvy can be caused, a disease that causes pain in joints and muscles and bleeding.
Food that contain it: Citrus fruits, raw vegetables
Vitamin D helps to absorb calcium for bones and teeth. Without this, rickets is caused where bones get soft and deformed.
Food that contain it: butter, egg yolk, sunlight
Minerals are inorganic substances that are needed in small amounts and they are needed.
Calcium is needed for bones and teeth and blood clotting and without it, it can cause bones to get brittle.
Food that contain it: milk (dairy products) bread
Iron is needed for making haemoglobin that carries oxygen and without it, it can cause anaemia when there aren’t enough red blood cells to carry oxygen
Foods that contain it: Liver, red meat, egg yolk, dark greeny vegetables
Fibre helps keep the alimentary canal to work properly because it is rough and causes the peristalsis to happen properly since softer foods do not stimulate the muscles It helps the muscles work well and this keeps the risk of constipation away. Fibre has cellulose and all fruits and vegetables contain it. (humans can not digest cellulose)
Foods that contain it: oats, wheat, barley, brown rice
Water makes up 60% of the human body. Cytoplasm is a solution of many substances in water and spaces between our cells are also filled with water. Cells have a lot of chemical reactions taking place in it and if the cell dries out, it dies and the reactions are stopped. The liquid in our blood is mostly water. Water is needed to dissolve enzymes and nutrients so that digestion can take place in the alimentary canal. Water also helps get rid of waste products – for example, kidneys excrete urea while it is diluted with water to form urine.
Foods that contain it: We get water from drinking fluids but some fruit contain water too.
7.2 The Human digestive system
The digestice system is a group of organs that work together to digest food. It includes the alimentary canal, liver, and pancreas. We need this so that we can absorb the food we eat into our blood.
The process of digestions:
Ingestion: taking the food into the mouth.
Digestion: contains 2 types, physical digestion – breaking down the large pieces of food into smaller pieces and chemical digestion – the small pieces into smaller molecules that can get through the walls of intestines.
Absorption: the moving of the small nutrients and mineral ions through the intestine into the blood.
Assimilation: The nutrients become a part of the body and are absorbed by individual cells used for energy.
Egestion: Sometimes, there is a lot of material that is not digested into our body - most of which is fibre and doesn’t get absorbed and hence passes out as faeces.
The Process:
1. The alimentary canal
This is a long tube that that runs from the tube all the way to the anus. It is a part of the digestive system.
The wall of the alimentary canal has muscles that contract and relax to make food move down – this is called peristalsis.
At times, food needs to be kept at one part of the alimentary canal before moving along and must be closed by muscles called sphincter muscles.
The alimentary canal is lubricated with mucus, a smooth fluid made out of goblet cells which is lined on the alimentary canal.
2. The mouth
Food is ingested with teeth, lips, and the tongue. The teeth grind the food into smaller pieces and this begins the physical digestion. The tongue mixes the food with saliva and makes it small balls that are swallowed.
The salivary glands make saliva which is a mixture of water mucus and amylase. The water dissolves the substances in the food, making us taste them. When it is turned into a ball, it slides down the oesophagus easily. Amylase digests starch.
Maryam
3. The oesophagus
There are two tubes that go down the back of the mouth – one the trachea/windpipe and the other, oesophagus/food pipe that takes food down to the stomach.
The centre of the oesophagus that the food gets down through is called the lumen.
The stomach:
The muscular walls in the stomach contract and relax to mix the food with enzymes and mucus
The stomach wall contains goblet cells that secrete mucus.
Other cells in the stomach produce enzymes which make hydrochloric acid.
The enzymes in the stomach are called proteases (because they digest proteins)
The stomach acid has a low pH, which helps in killing harmful bacterias in the food.
The stomach stores food for quite a while
After about 2 hours, the partly digested food is let into the duodenum through the sphincter, located at the bottom of the stomach.
4. The small intestine:
This organ is a part of of the alimentary canal located between the stomach and the colon
The small intestine is narrow and about 5 metres long
The first part of the small intestine is called duodenum
The last part is the ileum
All the digested nutrients are absorbed into the blood, this takes place in the ileum.
At this stage, water is also absorbed
The pancreatic duct is a tube that leads from the pancreas into the duodenum
5. The large intestine:
This organ is the last part of the alimentary canal.
It is made up of colon and rectum
Colon absorbs water still present in the food
Rectum stores undigested food (faeces)
These are then excreted from the body through the anus
The pancreas and liver:
The pancreas is a cream-colored gland which lies just below the stomach.
Pancreatic juice flows along the pancreatic duct into the duodenum.
Chemical digestion continues in the duodenum
The pancreas and liver are a part of the digestive system, however they are not included in the alimentary canal
Pancreas release a fluid containing enzymes and the liver secretes a fluid called bile. which helps with digestion in the duodenum.
The bile made by the liver is stored in the gallbladder.
Bile flows along the bile duct which mixes with the food after it enters the duodenum.
Bile is an alkaline, watery liquid which neutralizes the acidic mixture from the stomach.
Bile is yellowish-green in colour.
7.3 Digestion
Aaliya
The digestive system breaks down large food molecules (like starch, protein and fat) into smaller ones that the body can absorb
Digestion can occur in two stages:
Physical digestion - this is basically the mechanical breakdown of food into smaller pieces (its chewing with your teeth bro). It increases the surface area but does not change the chemical structure of the food.
Chemical digestion - Large molecules are broken down into smaller soluble molecules by enzymes. These reactions allow the nutrients to be absorbed into your blood.
Enzymes and products:
starch* is broken down by amylase into simple reducing sugars
protein* is broken down by protease into amino acids
fat* is broken down by lipase into fatty acids and glycerol
Tooth structure:
Enamel: The hardest substance in the body, covering the crown of the tooth. Its resistant to damage but can be dissolved by acids and bacteria
Dentine: Under the enamel, its not as hard but it is still strong. And it contains cytoplasm.
Pulp: Central part of the tooth with nerves and blood vessels.
Gum: soft tissue that surrounds and protects the tooth
Cement: it anchors the tooth/keeps it in place to the jawbone via fibres.
Jawbone: it supports the teeth and provides blood supply.
Types of teeth:
Humans have four types of teeth, each with a specific function:
Incisors - chisel - shaped, used for biting pieces of food
Canines - pointed teeth next to incisors, used for tearing food
Premolars - broad surfaces, used for grinding food
Molars - larger than premolars, also used for grinding at the back of the mouth
Key vocabulary:
Enamel - hard outer layer of the tooth.
Dentine - inner layer beneath the enamel, less hard
Cement - bone like substance that attaches the tooth to the jaw.
Incisors, canines, premolars, molars: different types of teeth, each adapted to a specific mechanical function in digestion.
The digestion that is done by the teeth and stomach breaks the food down into smaller pieces that increase its surface area, this helps enzymes can break the food apart more easily.
The different types of enzymes that help with digestion are:
Amylase is secreted by the salivary glands and is produced in the mouth/secreted by the pancreas in the duodenum
Protease is secreted by the walls of the stomach in the stomach/secreted by the pancreas in the duodenum
Lipase is secreted by the pancreas in the duodenum
Enzymes are are affected by pH and temperature and all of the enzymes work at the temperature 38℃ and this is normal body temperature. Stomach releases hydrochloric acid to kill bacteria so the protease can work at the pH 2 and this is optimum. The enzymes present in the duodenum require a pH of about 7 to work fastest. This pH is because of bile and pancreatic juice which is alkaline and neutralize the acid.
Zainab
Amylase - Secreted in: Mouth and duodenum - Breaks down: Starch to Maltose - Chewing starchy food for long can taste sweet (because of maltose) Maltase - Secreted in: Cell membranes of small intestine lining (aka epithelium) - Breaks down: Maltose to Glucose - Glucose is small enough to be absorbed - Maltase is not released into the intestine, it stays on the cells Proteins 2 types Pepsin - Works in: Stomach - Breaks down: Proteins to Amino acids - produced in: Stomach walls (in gastric juice) - Needs acidic conditions (optimum pH = 2) - Hydrochloric acid in stomach helps kill harmful microorganisms Trypsin - Works in: Duodenum - produced by: Pancreas - Breaks down: Proteins → Amino acids - Needs slightly alkaline pH (above 7) - Stomach acid is neutralised by bile and pancreatic juice Fats - Bile (not an enzyme) - Breaks large drops of fat and oil to tiny droplets (emulsification) - Emulsification = physical digestion - Makes fat easier for enzymes to work on (increases surface area) Lipase - Works after bile does emulsification - Breaks down: Fats to Fatty acids + Glycerol PDF version
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