CIE A Level Biology (9700) 2019-2021

Revision Notes

14.1.2 Nervous System & Endocrine System

Coordinating Homeostatic Mechanisms

  • Homeostatic mechanisms help organisms to keep their internal body conditions near constant
  • Three key homeostatic mechanisms are:
    • Thermoregulation – the control of body temperature
    • Osmoregulation – the control of the water potential of body fluids
    • The control of blood glucose concentration
  • These homeostatic mechanisms in mammals require information to be transferred between different parts of the body
  • There are two coordination systems in mammals that do this:
    • The nervous system
    • The endocrine system

The nervous system

  • The human nervous system consists of:
    • The central nervous system (CNS) – the brain and the spinal cord
    • The peripheral nervous system (PNS) – all of the nerves in the body
  • It allows us to make sense of our surroundings and respond to them and to coordinate and regulate body functions
  • Information is sent through the nervous system as nerve impulses – electrical signals that pass along nerve cells known as neurones
  • A bundle of neurones is known as a nerve
  • Neurones coordinate the activities of sensory receptors (eg. those in the eye), decision-making centres in the central nervous system, and effectors such as muscles and glands

The endocrine system

  • A hormone is a chemical substance produced by an endocrine gland and carried by the blood
    • They are chemicals which transmit information from one part of the organism to another and bring about a change
    • They alter the activity of one or more specific target organs
  • Hormones are used to control functions that do not need instant responses
  • The endocrine glands that produce hormones in animals are known collectively as the endocrine system
    • A gland is a group of cells that produces and releases one or more substances (a process known as secretion)
  • Endocrine glands have a good blood supply as when they make hormones they need to get them into the bloodstream (specifically the blood plasma) as soon as possible so they can travel around the body to the target organs to bring about a response
  • Hormones only affect cells with receptors that the hormone can bind to
    • These are either found on the cell surface membrane, or inside cells
    • Receptors have to be complementary to hormones for there to be an effect

Features of the nervous system & the endocrine system table

Comparing the features of the nervous & endocrine system table, downloadable AS & A Level Biology revision notes


Alistair graduated from Oxford University in 2014 with a degree in Biological Sciences. He has taught GCSE/IGCSE Biology, as well as Biology and Environmental Systems & Societies for the International Baccalaureate Diploma Programme. While teaching in Oxford, Alistair completed his MA Education as Head of Department for Environmental Systems and Societies.

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