CONTROL IN THE BODY A2

1
CONTROL IN THE BODYA2

• TO BE ABLE TO DESCRIBE THE MAIN CONTROL
  MECHANISMS AND IMPORTANCE OF HOMEOSTASIS.

2
HOW ARE ORGANISMS AND SYSTEMS CONTROLLED?

• Most animals and plants are complex, made of
  millions of cells.
• Different parts of organisms perform different
  functions.
• Its essential that info can pass between
  different parts to co-ordinate their activities.

3
Carrying on

• Sometimes the purpose of the info transfer is to
  regulate levels of some substance within the
  organism. e.g
• Sometimes the purpose may be to change the
  activity of some part of the organism in response
  to an external stimulus. e.g

4
CHEMICAL MESSENGERS AND NERVES.

• .In both animals and plants, chemical messengers
  called HORMONES help to transfer info from one
  part to another to achieve co-ordination.
• In many animals, including mammals, NERVES
  transfer info in form of electrical impulses.

5
HOMEOSTASIS

• A vital function of control systems is to
  maintain a stable internal environment.
• This is called HOMEOSTASIS.
• Internal environment means the conditions inside
  the body, in which cells function.

6
Homeostasis

• Why is homeostasis important?
• What factors need to be kept at constant levels,
  why?

7
Homeostasis..

• All cells need to be in the best physical and
  chemical conditions possible if they are to
  function properly.
• Keeping every cell at the optimum temp, with
  enough water and glucose is a complex task that
  involves many systems in the body.

8
Homeostasis.

• Many cells are highly specialised and are
  physiologically demanding if they are to perform
  to their optimum level.
• Many features of the environment affect the
  functioning of the cells and have to be
  controlled in their effect.

9
Homeostasis

• Biologists call this overall control mechanism
  HOMEOSTASIS
• Literally - steady state.
• It refers to the fact that conditions inside the
  body, especially in the tissue fluid, need to be
  maintained within certain limits.
• Some are kept within narrow limits and others
  vary over a wider range.
• E.g..

10
Responding to a change

• Change in conditions
• Detected
• Corrected

11
POINTS FOR FOCUS IN HOMEOSTASIS.

• What causes the change?
• A rise in air temp may cause an increase in body
  temp.
• What detects the change?
• If body temp starts to rise it is detected by
  hypothalamus in brain.
• How is change corrected?
• To reduce its temp the body sweats and
  vasodilation takes place.

12
Examples of Homeostasis

• From AS you have looked at controlling the water
  potential of blood.
• Body temp was looked at briefly in the SAVOL
  ratio section of AS.
• Control of blood acidity was studied in mod 3.

13
AT A2 WHAT WILL YOU STUDY?

• You will look at homeostatic mechanisms in the
  human body that keep blood glucose concentration
  and body temperature within set limits.

14
Stimulus And Response.

• Homeostasis involves mechanisms that correct
  changes in the body.
• Changes are usually due to a stimulus that can be
  INTERNAL or EXTERNAL.
• TASK
• Describe this situation, the response and the
  effect in the control of blood sugar.

15
Stimulus and Response

• Write a simple stimulus response pathway.

16
Stimulus and Response
Stimulus
Receptor
Coordinator
Effector
Response
Receptor detects increase
Coordinator stimulates effector
Normal levels
Response reduces levels back to normal
17
NEGATIVE FEEDBACK SYSTEMS.

• Receptors and effectors work together in
  homeostatic control systems in FEEDBACK SYSTEMS.
• These are usually negative feedback systems.
• Explain positive and negative feedback control in
  homeostasis