Coordination and Control - Control of Internal Conditions

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Coordination and Control
Menstrual Cycle
Control of Fertility
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Control of Internal Conditions

In order for your body to work properly it's internal environment must be kept constant.  Enzymes which control many of the the body's processes work best at 37oC.  Changing amounts of water and sugar can affect chemical reactions that are essential for you body to work properly.  Internal conditions which are controlled include:

  • The water content of the body.  Water leaves the body when we breathe out and through the skin when we sweat.  Any excess water is also lost via the kidneys in urine when we go to the toilet.
  • The ion (salt) content of the body.  Ions (salt) are lost via the skin when we sweat.  Excess ions are also lost via the kidneys in urine.
  • Temperature.  Your body temperature is kept very close to 37oC to maintain the temperature at which enzymes work best.
  • Blood sugar levels.  When you digest carbohydrates lots of sugar (glucose) passes into your blood.  Hormones made in the pancreas keep the blood sugar level at a constant level to provide your cells with a constant supply of energy.  The hormone insulin reduces blood sugar levels if they become too high.  Another hormone causes the blood sugar level to rise if it becomes too low.  People who suffer from diabetes often need to inject themselves with insulin to help control their blood sugar levels.  If your blood sugar levels become too high or too low this causes chaos in your body.


Many processes in the body are controlled by chemical substances called hormones.  Hormones are released into the blood (secreted) by glands.  The hormones are transported to their target organs by the bloodstream.  The target organ is where the hormone has an effect.  The diagram below shows some of the glands in the body where hormones are made.  (Glands which release hormones into the blood are called endocrine glands).


The diagram shows some of the major glands that release hormones into the blood.  The pancreas releases the hormones insulin and glucagon which control the blood sugar level.  The role of these hormones will be discussed in detail in Module B2.  The pituitary gland releases the hormones FSH and LH.  These are involved in the control of the female menstrual cycle.  Their target organs are the ovaries.  The ovaries also make hormones such as oestrogen.  The role of these hormones in the control of the menstrual cycle is discussed in the next section.