• A?hormone?is a chemical substance produced by a?gland?and?carried by the blood, which alters the activity of one or more specific?target organs
  • They are chemicals that transmit information from one part of the organism to another and bring about a?change

   

• The following hormones are of great importance in humans:
  • Adrenaline
  • Insulin
  • Testosterone
  • Progesterone
  • Oestrogen

   

Adrenaline and how it prepares the body for action

• Adrenaline is known as the?'fight or flight'?hormone as it is produced in situations where the body may be in?danger
• It causes a?range of different things?to happen in the body, all designed to?prepare it for movement?(i.e. fight or flight).
• These include:
  • An?increase in heart rate and breathing rate?- ensures?glucose?and?oxygen?can be delivered to?muscle cells?(and carbon dioxide can be taken away from muscles cells) at a?faster rate
  • Diverting blood flow towards muscles?and away from non-essential parts of the body such as the alimentary canal - ensures an?increased supply of the reactants of respiration?(glucose and oxygen)
  • Dilation of the blood vessels inside muscles?- ensures?more blood?can circulate through them (again, supplying?more glucose and oxygen)
  • Breaking down of stored glycogen to glucose?in the liver and muscle cells, with glucose released by the liver being transported to active muscle cells - ensures a?higher blood glucose concentration?for?increased respiration?in muscle cells (providing?greater energy for movement)

   

Insulin and how it controls blood sugar

• Blood glucose concentration must be kept within a?narrow range, so it’s another example of?homeostasis?(like the control of core body temperature)
  • Too high a level of glucose in the blood can lead to cells of the body losing water by osmosis, which can be dangerous
  • Too low a level of glucose in the blood can lead to the brain receiving insufficient glucose for?respiration, potentially leading to a coma or even death

   

• The?pancreas?and?liver?work together to?control blood glucose levels
• To carry out this role, the pancreas acts as an?endocrine gland?(making and secreting?hormones?into the?bloodstream), although it does also plays a vital (but separate) role in digestion (making and secreting enzymes into the digestive system)
• If the blood glucose concentration gets too high:
  • Cells in the pancreas detect the increased blood glucose levels
  • The pancreas produces the hormone?insulin, secreting it into the blood
  • Insulin stimulates?muscles?and the?liver?to?take up glucose?from the bloodstream and?store it as glycogen?(a polymer of glucose)
  • This?reduces?the concentration of glucose in the blood back to normal levels, at which point the pancreas stops secreting insulin

   

• If the blood glucose concentration gets too low:
  • Cells in the pancreas detect the decreased blood glucose levels
  • The pancreas produces the hormone?glucagon
  • Glucagon causes the?glycogen?stored in the?liver?to be?converted into glucose?and released into the blood
  • This?increases?the concentration of glucose in the blood back to normal levels, at which point the pancreas stops secreting glucagon

   

The regulation of blood glucose levels

Testosterone

• Testosterone is produced in the male testes
• It is responsible for the development of secondary sexual characteristics in males

Progesterone

• Progesterone is produced in the female ovaries
• It is responsible for maintaining the uterine lining during pregnancy

Oestrogen

• Oestrogen is produced by the female ovaries
• It is responsible for the development of secondary sexual characteristics in females and regulating the menstrual cycle

Important Hormones in the Human Body Table