Edexcel IGCSE Biology: Double Science 复习笔记 2.10.12 The Role of Hormones

Edexcel IGCSE Biology: Double Science 复习笔记 2.10.12 The Role of Hormones

The Role of Hormones: Basic

 

  • 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

     

 

 

Negative-feedback-regulation-of-blood-glucose-levels

 

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

important-hormones_-basic_1

 

 

Exam Tip

It is worth learning this list of effects of adrenaline on the body as it is a fairly common exam question and can be worth several easy marks.Also, be careful when answering questions on the control of blood glucose levels - the terms glucagon and glycogen are very often mixed up by students as they sound similar.

  • Glucagon is a hormone
  • Glycogen is a polysaccharide (i.e. the polymer of glucose that acts as a glucose storage molecule)

Learn the differences between the spellings and what each one does so you don't get confused in the exam!

转载自savemyexams

 

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