Hormones in Humans (Cambridge (CIE) IGCSE Biology): Revision Note

Hormones & their associated glands

What is a hormone?

• 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

  • In other words, hormones are chemical messengers that transmit information from one part of the body to another, bringing about a change

• Collectively, the hormone-producing glands in the body form the endocrine system

Transport around the body

• Endocrine glands have a good blood supply, allowing hormones to enter the bloodstream (specifically the blood plasma) quickly, so they can travel around the body to target organs and bring about a response

• Hormones only affect cells that have target receptors complementary to that hormone, allowing it to bind

• Target receptors may be found on the cell membrane or inside the cell

• The liver regulates levels of hormones in the blood; transforming or breaking down any that are in excess

 Important hormones in the human body

Comparison of nervous & hormonal control

Glucagon: Extended

• Blood glucose levels are controlled by a negative feedback mechanism involving the production of two hormones: insulin and glucagon

• Both hormones which control blood glucose concentration are made in the pancreas

• Insulin is produced when blood glucose rises and stimulates liver and muscle cells to convert excess glucose into glycogen to be stored

• Glucagon is produced when blood glucose falls and stimulates liver and muscle cells to convert stored glycogen into glucose to be released into the blood

The hormone adrenaline

• Adrenaline is known as the 'fight or flight' hormone as it is produced in situations where the body may be in danger

  • Flight: remove oneself rapidly from a dangerous situation e.g. run away

  • Fight: if flight is not possible, resort to physical combat to overcome 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)

• These include: 

  • increasing blood glucose concentration for increased respiration in muscle cells

  • increasing pulse rate and breathing rate so glucose and oxygen can be delivered to muscle cells, and carbon dioxide taken away, from muscles cells more quickly

  • diverting blood flow towards muscles and away from non-essential parts of the body such as the alimentary canal; again to ensure the reactants of respiration are as available as possible

  • dilating pupils to allow as much light as possible to reach the retina so more information can be sent to the brain

More on adrenaline: Extended

• Additional effects of adrenaline include:

  • increasing the concentration of glucose in the blood

    • This help deliver more important glucose to muscles for respiration

  • increasing heart rate

    • This has the same effect, to ensure that all muscles are well prepared for high levels of activity in a flight or fight situation