The Role of Hormones: Basic (Edexcel IGCSE Biology): Revision Note

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

• Adrenaline causes a range of different things to happen in the body, all designed to prepare it for movement (i.e. fight or flight)

• Effects of adrenaline include:

  • Increased heart rate and breathing rate – delivers glucose and oxygen to muscle cells faster and removes carbon dioxide more efficiently

  • Redirects blood flow to muscles and away from non-essential organs (e.g. the alimentary canal) – ensures muscles receive more oxygen (and glucose) for respiration

  • Dilation of blood vessels in muscles – allows more blood (and therefore glucose and oxygen) to reach active muscles

  • 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, which can be used in respiration by muscle cells

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 stimulating the development of male reproductive organs and the development of secondary sexual characteristics in males (facial/pubic/underarm hair, deepening of voice, increased muscle mass)

Progesterone

• Progesterone is produced in the female ovaries

• It is responsible for maintaining the uterine lining during pregnancy and prevents further ovulation

Oestrogen

• Oestrogen is produced by the female ovaries

• It is responsible for:

  • The development of secondary sexual characteristics in females (breast development, wider hips, pubic/underarm hair)

  • Regulating the menstrual cycle by stimulating the repair of the lining of the uterus (endometrium) after menstruation and helps control the release of eggs (ovulation) by influencing other hormones (such as FSH and LH)

Summary of hormones and their functions table