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Carbohydrates contain the elements carbon, hydrogen & oxygen
Fats contain the elements carbon, hydrogen & oxygen
Proteins contain the elements carbon, hydrogen, oxygen & nitrogen
Carbohydrates Carbohydrates provide us with energy for our normal activities. They consist of long chains of glucose molecules. Glucose
Fats Fats release some energy for our use if required while the rest is stored in adipose tissue beneath the skin. This is used as insulation. Each fat is made up of a glycerol molecule joined to 3 fatty acid molecules. Glycerol Fatty acid Fatty acid Fatty acid
Proteins Our body requires protein to build it up and for repairing damaged tissue. Proteins are built up from long chains of amino acids. There are only about 20 different amino acids.
The Need for Food
Our food is a mixture of solids and liquids containing, among other things, carbohydrates and fats for energy and proteins for growth and repair.
In order for the food to be of any use it has to reach every cell in the body.
This is done by the blood, but in order to be carried in the blood the food must dissolve.
Before the food leaves the gut, it must be soluble.
The Need for Food
Mammals, throughout the world, are adapted to almost every type of environment and the wide variety of food sources they contain.
There are basically 3 types of mammal:
Herbivores – animals which eat only plants.
Carnivores - animals which eat other animals.
Omnivores - animals which eat both plants and other animals.
Teeth of a Herbivore Upper jaw of a sheep Lower jaw of a pig Note the ridges on the molars & premolars Note the gap between the incisors and the premolars
Skull of a Rabbit
Teeth of a Carnivore Skull of a Fox Note the large canines Note the shape of the premolars and molars
Skull of a Dog
basically have 4 types
of teeth – all suited to
Incisors – found at the front and used for biting, gripping and pulling. Canines – used for gripping and tearing.
Teeth An animals teeth are suited to what it eats. Molars – found at the back and used for crushing and grinding. Premolars – used for crushing and grinding.
Can YOU name the parts? Enamel Dentine Pulp Crown Gum Bone Root Nerves & Blood vessels
Location of Teeth
The human gut is sometimes called the alimentary canal.
It is a tube about 5m long.
It runs from the mouth to the anus.
It is coiled up to fit in the body.
Digestive System 1= Mouth 3= Tongue 2= Teeth 4= Stomach 5= Pancreas 6= Small intestine 7= Rectum 8= Salivary Glands 9= Oesophagus 10= Liver 11= Gall Bladder 12= Large intestine 13= Appendix 14= Anus
Can YOU name the Parts? Mouth Oesophagus Liver Stomach Gall Bladder Colon Appendix Pancreas Small intestine Rectum Anus
Food cannot move through the gut by itself.
It must be pushed.
This is done using the muscles in the gut wall which contract and relax to force the food along.
This process is called peristalsis .
If we drink water upside down it will not run back out.
The food is physically broken down into manageable sizes by the teeth.
It is mixed with a fluid called SALIVA.
It contains enzymes to digest food.
This makes the food easier to swallow.
The food is then moved through the gullet (oesophagus) to the stomach.
The stomach is a muscular bag with a valve at either end.
The CARDIAC sphincter at the top allows food in.
The PYLORIC sphincter at the bottom allows food to leave.
The stomach wall produces digestive juices which chemically break down some of the large molecules of food.
For digestion to work properly the food must be well mixed with the juices.
The stomach muscles contract and relax to mix up the juices and food.
Once the food has been in the stomach for a while, it is released slowly, small drops at a time into the small intestine.
Small Intestine (Duodenum & Ileum)
Digestion continues in the small intestine.
The final products are then absorbed through the intestine wall.
Absorption will happen quicker if the surface area of the inside of the small intestine is increased.
The length of the small intestine increases the surface area, but so also do the VILLI (small finger-like projections.)
Small Intestine (Duodenum & Ileum)
Once digestion is complete, the products pass through the thin wall into the blood capillaries to be transported away to other parts of the body for use.
The VILLI are adapted to absorbing food by their very thin wall, large surface area and excellent blood supply.
Glucose and amino acids enter the blood capillaries.
The blood capillaries all enter the Hepatic Portal Vein which leads from the intestine to the liver.
Fatty acids and glycerol enter the LACTEAL which is a part of the lymphatic system.
Diagram of a Villus
Large Intestine (Colon)
The undigested food passes from the small intestine into the colon.
The colon removes water from the undigested food to make it semi-solid.
After this, the food is stored in the rectum before it is eliminated through the anus.
Digestion in the gut involves the chemical breakdown of food. Each type of food is broken down by a different chemical (enzyme) e.g.
Amylase breaks down starch
Pepsin breaks down protein
Lipase breaks down fats
The main digestive juices are produced by the salivary glands, stomach, liver, pancreas and small intestine.
Most digestive juices contain enzymes.
Bile, which is produced by the liver and stored in the gall bladder, has no enzymes.
There are 3 different groups of enzymes involved in digestion.
Each group acts on a different type of food, called the SUBSTRATE.
The substrate gets broken down by the enzymes to substances called PRODUCTS.
During digestion large molecules are broken down to small molecules to allow them to pass into the blood.
Passes through gut wall Cannot pass through gut wall Soluble Insoluble Small molecule Large molecule Glucose Starch
Digestion “ Digestion is the breakdown of large insoluble molecules to small soluble molecules so that they can pass through the gut wall.”
The layers of muscle in the gut wall are required for the process of PERISTALSIS.
The wall of the gut constricts behind the food to push the food along.
The gut get wider in front of the food to let it through.
There is a wave of relaxation to push the food along – a bit like forcing a tennis ball into a sock.
Peristalsis occurs along the whole length of the gut from the mouth to the anus.
Peristalsis Muscles contract here Food moves this way Muscles relax here
Balanced Diet A healthy diet must contain some food from all of the following groups:
Carbohydrates and fats provide us with energy.
Proteins are used to build and repair body tissue.
Fibre gives the gut muscles something to work against to avoid constipation.
Plant fibre is found in fruit and vegetables and especially bran which surrounds cereal grains.
Vitamins and minerals are used to maintain health.
Some of the food we eat is fresh, e.g. apples and lettuce.
Mostly, however, our food has been processed in some way to make it more attractive, to change its flavour, or to keep it longer.
Processing food often involves adding chemicals called additives.
Vitamins Blood doesn’t clot Green veg. K Reproductive Disorders Wheat germ E Rickets Liver, fish, milk D Scurvy Citrus fruits C (Ascorbic acid) Pellagra Cereal, lean meat B 3 (Niacin) Beri beri Cereal grains B 1 (Thiamine) Night Blindness Milk, fresh veg. A Deficiency Disease Source Vitamin
Minerals Healthy teeth & bones Calcium All cells Sodium Thyroxine Iodine Haemoglobin in Red Blood Cells Iron Required For: Mineral