The Role of Hormones: Basic (Edexcel IGCSE Science (Double Award))
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The Role of Hormones: Basic
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
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
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 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
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
Summary of hormones and their functions table
Hormone | Source | Role | Effect |
---|---|---|---|
Adrenaline | Adrenal gland | Readies the body for a 'fight or flight' response | Increases heart and breathing rate |
Insulin | Pancreas | Lowers blood glucose levels | Causes excess glucose in the blood to be taken up by the muscles and liver and converted into glycogen for storage |
Testosterone | Testes | Main sex hormone in males | Development of male reproductive organs and secondary sexual characteristics |
Progesterone | Ovaries | Maintains pregnancy | Maintains the uterus lining to cushion the fertilised egg and allow it to develop |
Oestrogen | Ovaries | Main sex hormone in females | Development of female secondary sexual characteristics and regulation of the menstrual cycle |
Examiner Tips and Tricks
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.
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