Homeostasis Flashcards
What is homeostasis?
The maintenance of the internal environment within an optimum range
State an example of a stimulus in the external environment and a corresponding response in animals
- Cooler environment -> arctic fox grows a much thicker coat in winter (gradual response)
- warmer environment -> moving into the sunlight
- appearance of a predator -> fleeing
State an example of a stimulus in the internal environment and a corresponding response in animals
Stimulus: Build up of waste products eg. Carbon dioxide in respiration -> response: removal of these products by cells
How is the internal environment maintained?
Composition of the tissue fluid is maintained by the blood as toxins enter and are carried away. They must be removed by excretion to prevent accumulation in the blood.
What is the neuronal system?
A network of neutrons that signal across synapse junctions through neurotransmitters. They can conduct quickly and therefore elicit rapid responses to stimuli
What is the hormonal system?
A system that uses blood to transport its signals. Cells in an endocrine organ release a hormone directly into the blood which are recognised by target cells. These create longer term responses to stimuli
What factors to homeostasis maintain?
- Body temperature
- blood glucose conc
- blood salt conc
- water potential of the blood
- blood pressure
What are sensory receptors?
They monitor changes in the external or internal environment and stimulate cell signalling
Eg. Temperature receptors on the skin
What is negative feedback?
When a change away from the optimum occurs negative feedback counteracts this
Change from optimum -> receptor detects change -> communication system informs effector -> effector acts to reverse change -> return to optimum
What is positive feedback?
When a change occurs and the response is to increase that original change. It is often harmful eg. In enzyme controlled reactions. However it can be useful
What is an overshoot?
When a stimulus occurs but it takes a while for the body to produce a response
What is an ectotherm?
They aren’t able to control their body temp as effectively, rely on external sources of heat and body temp fluctuates with environment
How is temperature regulated in ectothermic?
Behavioural responses:
- move into sunny area/shade
- lie on warm surface/move underground
- expose a large/smaller area of the body to the sun
What are some advantages of ectothermy?
- less of their food is used up during respiration
- more nutrients gained from food can be converted to growth
- need to find less food/can survive without it for longer
What are some disadvantages of ectothermy?
- less active in cooler temperatures
- at risk from predators when cold
What are endotherms?
They do not rely on external sources of heat - use physiological adaptations to control temp
What are some mechanisms used to regulate temperature in endotherms?
-Skin: sweat glands secrete fluid
hairs and feathers lie flat to reduce insulation / stand erect to trap air
vasodilation / vasoconstriction
-less respiration takes place in the liver so less heat released / more respiration
-fewer contractions / shivering
Same behavioural responses as ectotherms
What is
A) vasodilation?
A) sphincters are open to allow blood to flow to the extremities to increase heat loss
B) sphincters are closed to restrict blood from flowing to the extremities so it isn’t cooled too much- can lead to frostbite
What are some advantages of endothermy?
- Maintain constant body temp despite external temperature
- can remain active and take advantage of prey/escape predators while cold
What are some disadvantages of endothermy?
- require more food
- lower proportion of the energy from food is used for growth
What is thermoregulation?
Temp receptors on the hypothalamus detect change and send out impulses to cause different responses eg. Changes in skin to reduce heat loss, shivering, increased metabolism. Controls rapid responses
What is the role of peripheral temp receptors?
They monitor the temperature in the extremities which is fed to the thermoregulatory centre in the hypothalamus. Detect external temperature so the brain can initiate behavioural mechanisms for maintaining body temp prior to temp change in the body.
