Ask mr Brain...all will be explained

PUBLISHED : Saturday, 17 July, 1999, 12:00am
UPDATED : Saturday, 17 July, 1999, 12:00am
 

Why do I feel sleepy after lunch? After eating food, such as at lunch, the rate at which the body uses energy - its metabolic rate - goes up. A lot of energy is needed to digest the new intake of food in your digestive system so less is available to other parts of the body.


Metabolic rates depend on how much and how often animals eat. In mammals, including humans, metabolism goes up by between 25 and 50 per cent. A meal will spend approximately three to four hours in the stomach where it is broken down. By late afternoon, it will have moved into the small intestine where digestion continues. These processes in themselves use up a lot of energy but a hormone called cholecystokinin, released during digestion, seems to activate areas in the brain involved in sleep which contribute to making you feel sleepy. Another of cholecystokinin's roles is to make you feel full after a meal.


In addition, when carbohydrates, found in rice, spaghetti and bread are digested, the level of an amino acid called tryptophan increases in the blood stream. Tryptophan is converted into another chemical called serotonin when it reaches the brain. And, guess what, serotonin makes you drowsy! So there are sound scientific reasons for wanting a nap after lunch. It's not just laziness.


What is the difference between Great Britain, England and the United Kingdom? ESTHER LI St Stephen's College England as an entity has been in existence since the 10th century. The term Great Britain was first used by King James I (who was also James VI of Scotland) when he acceded to the throne of England and Wales in 1603 and called himself King of Great Britain.


It wasn't until the Act of Union in 1707 that Scotland officially agreed to permanent union as part of Great Britain. Today, Great Britain means the island that is made up of England, Scotland and Wales and various islands.


However, the Channel Islands in the English Channel and the Isle of Man off northwest England are not part of Great Britain, they are British dependencies.


The United Kingdom is the islands of Great Britain plus Northern Ireland. Often people (including those living in Britain) wrongly use 'England' to mean Britain or the United Kingdom, which people in Northern Ireland, Scotland and Wales often take offence at.


In short, England is a part of Great Britain, which in turn, is a part of the United Kingdom.


Is it possible to get a suntan from behind glass? It is exposure to ultraviolet rays of a frequency between 280 and 320 nanometres in sunshine that causes our skin to darken or tan. Although ordinary glass absorbs some of the UV rays in this range, between 1.6 per cent and 71 per cent still get through. So it is possible to get tanned from behind glass but it will take longer. But glass can also bend and focus light rays so areas of your skin could be in danger of burning instead of just tanning.


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