B1aL3 In Control

Key Words

Effector - organs the respond to nervous impulses.
Enzymes - biological catalysts that are always proteins.
Glucose - a sugar used for energy in the blood.
Hormone - a chemical released into the blood that makes an organ or number of organs respond in a particular way.
Insulin - a protein based hormone that is made by the pancreas to regulate glucose levels.
Ions - charged atoms.
Liver - a large organ below the diaphragm that processes toxic materials and stores glucose.
Pancreas - a small organ below the stomach that releases digestive enzymes and insulin.
Receptor - nerve cells that detect changes.
Salt - sodium chloride, NaCl.

Salts - chemical compounds that are made up of a positive ion and a negative ion.
Sweating - excretion of water to the surface of the skin, the evaporation of which cools the body.

Grade E

The body is a very delicately balanced system.  If it goes unbalanced, it can be damaged, possibly fatally.  So there are all sorts of mechanisms that the body uses to keep balanced.

The body can survive several weeks without food; without water, death will occur in a few days.  Some people trapped in the ruins of houses wrecked by earthquakes have died through lack of water, even though they weren't hurt.  On the other hand, people have survived many days because they have been able to find water.

Too much water can be dangerous; it moves into cells and the cells can burst.

We take in water and ions through our mouths, and they are absorbed through the stomach.

The water is lost as we breathe out and sweat to keep cool.  Salt is lost through sweating as well.  The two young men in the picture above will need to drink water at the end of their race to make up what is lost due to sweating.

Their kidneys will regulate the amount of water lost through urine, as well as the salts that are removed.  When they are running (and sweating) their kidneys will reduce the amount of water lost.  They will also check that the salt levels are maintained.  The control of the kidneys is maintained by hormones and nerve activity.

Grade C

Body temperature needs to be kept at about 37 ^oC.  Anything above 40 degrees, then the enzymes start to break down.  This is called heat-stroke.  Anything colder than 35 degrees, the enzyme rate slows down.  This is called hypothermia.   Both are potentially fatal.  The way the body controls temperature is shown in the diagram:

Sweat is released by sweat glands in the skin.  Water which has its origin from the blood comes up to the surface.  The water evaporates, a process that needs a lot of energy. 

Therefore energy is extracted from the body, and the body cools down. 

This is called thermoregulation and has a feedback mechanism.  However, if there is not enough water in the body, there is the risk of the blood getting too thick, and the body overheating.  Both of these can be dangerous. 

Water is controlled by a similar feedback mechanism using the kidneys as shown in the diagram.

The two young men in the picture above will therefore need to drink.

Manufacturers of sports drinks will tell athletes that they need to drink a mineral-fortified fizzy drink to replace the minerals.  Wrong.  The body has a large reserve of minerals and the kidneys will keep the mineral balance just right.  So a top up of water is just as good and a lot cheaper.  As for minerals, they will be replaced in the next meal.  Sports drinks are hyped up versions of carbonated (fizzy) sugar solutions.  They do as much good as the over-marketed products for detox, which the liver does perfectly well on its own.

They will also need sugar for the energy.  The sugar level is kept constant by the pancreas, an organ that is found below the stomach.

It works in conjunction with the liver which breaks down a material called glycogen (very similar to starch in plants) into glucose, a sugar.  The rate of conversion is controlled by hormones from the pancreas. 

Should the pancreas fail to produce these hormones, the sugar levels start to vary, a condition called diabetes.

Grade A

In the picture above, the young men will also lose water in other ways as they run.  They will breathe water out as a waste product from the lungs as they run.  Their muscles will generate a lot of heat, so they will need to sweat.  On a warm day, as it was when the race was run, heat will also enter the body from the sun.

The kidneys will regulate how much water is lost under the influence of hormones.  This is achieved by "pumping" water back into the blood.  The mechanism for this is studied at A- level.  A certain amount of water has to be lost, to remove waste materials such as urea.