Homeostasis and response

4.5 Homeostasis and response

Cells in the body can only survive within narrow physical and chemical limits. They require a constant temperature and pH as well as a constant supply of dissolved food and water. In order to do this the body requires control systems that constantly monitor and adjust the composition of the blood and tissues. These control systems include receptors which sense changes and effectors that bring about changes. In this section we will explore the structure and function of the nervous system and how it can bring about fast responses. We will also explore the hormonal system which usually brings about much slower changes. Hormonal coordination is particularly important in reproduction since it controls the menstrual cycle. An understanding of the role of hormones in reproduction has allowed scientists to develop not only contraceptive drugs but also drugs which can increase fertility.

4.5.1 Homeostasis

Content

Key opportunities for skills development

Students should be able to explain that homeostasis is the regulation of the internal conditions of a cell or organism to maintain optimum conditions for function in response to internal and external changes.

Homeostasis maintains optimal conditions for enzyme action and all cell functions.

In the human body, these include control of:

blood glucose concentration

body temperature

water levels.

These automatic control systems may involve nervous responses or chemical responses.

All control systems include:

cells called receptors, which detect stimuli (changes in the environment)

coordination centres (such as the brain, spinal cord and pancreas) that receive and process information from receptors

effectors, muscles or glands, which bring about responses which restore optimum levels.

4.5.2 The human nervous system

4.5.2.1 Structure and function

Content

Key opportunities for skills development

Students should be able to explain how the structure of the nervous system is adapted to its functions.

The nervous system enables humans to react to their surroundings and to coordinate their behaviour.

Information from receptors passes along cells (neurones) as electrical impulses to the central nervous system (CNS). The CNS is the brain and spinal cord. The CNS coordinates the response of effectors which may be muscles contracting or glands secreting hormones.

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Students should be able to explain how the various structures in a reflex arc – including the sensory neurone, synapse, relay neurone and motor neurone – relate to their function. Students should understand why reflex actions are important.

Reflex actions are automatic and rapid; they do not involve the conscious part of the brain.

Students should be able to extract and interpret data from graphs, charts and tables, about the functioning of the nervous system.

MS 2c

Students should be able to translate information about reaction times between numerical and graphical forms.