IGCSE Double Award Extended Coordinated Science
Biology 7.4 - Homeostasis
Homeostasis
You need to know​ that ​homeostasis​ is:
- The regulation of internal body conditions ​or​ the maintenance of a constant internal environment.
When a certain value in the body (e.g. temperature) is not its normal value because of changes in the environment,
- The body adjusts so that it is returned to normal value (opposes the change in the environment)
- This is called ​negative feedback
- This is the logic behind​ homeostasis.
- Keeps the body in correct conditions
Temperature control
The skin has many features which allow homeostasis:
- Temperature receptors
- Detect change in temperature (too hot or cold) and sends a message to adjust the body accordingly.
- Sweat glands
- Produces and secretes sweat through the pores to cool down the body if it gets too hot
- Blood Capillaries
- By vasoconstricting and vasodilating, it can control the loss of heat through the blood capillaries
- When cold, vasoconstricting pulls the vessels closer in the body, minimising heat loss
- When hot, vasodilating allows the vessels to be closer to the surface, to lose heat
- This is why when some people go for a run, their faces turn red.
- Hair and hair muscles
- Hair muscles allow the hair to stand up and this allows the hair to trap air
- Air is a good insulator of heat, so it minimises heat loss when cold.
Blood glucose level control
The pancreas produces two hormones which allow the liver to change blood glucose levels
- Insulin​ - tells the liver to ​decrease blood glucose level​ by converting glucose into glycogen
- Glucagon​ - tells the liver to ​increase blood glucose level ​by breaking down glycogen
With negative feedback,
- When blood glucose level is too high, the pancreas produces insulin
- To decrease the blood glucose level
- When blood glucose level is too low, the pancreas produces glucagon
- To increase the blood glucose level
This allows the blood glucose level to be at the right level.
The syllabus says you should be able to, (SO check if you can):
- Define homeostasis as the maintenance of a constant internal environment.
- Identify, on a diagram of the skin: hairs, sweat glands, temperature receptors, blood vessels and fatty tissue.
- Describe the maintenance of a constant body temperature in humans in terms of insulation and the role of
temperature receptors in the skin, sweating, shivering, vasodilation and vasoconstriction of arterioles
supplying skin-surface capillaries and the coordinating role of the brain.
- Explain the concept of control by negative feedback.
- Describe the control of the glucose content of the blood by the liver, and by insulin and glucagon from the
pancreas.