OCR A Biology - Module 5 - Communication & Homeostasis

Why is a good communication system required?

To ensure different parts of the body work together effectively

Factors of a good communication system

* Covers the whole body
* Enables cells to communicate with each other
* Enables specific & rapid communication
* Enables both short & long-term responses

What is the Neuronal System of communication?

An interconnected network of neurones that signal each other across synapse junctions

Neurones can conduct a signal very quickly & enable rapid responses to changing stimuli

What is the Hormonal System of communication?

A system uses the blood to transport its signals

Hormones are released from an endocrine organ directly into the blood & travel through the body

These are only recognised by specific target cells

What is Homeostasis?

Keeping a constant internal environment

Examples of aspects maintained by homeostasis

* Body temperature
* Blood glucose concentration
* Blood salt concentration
* Water potential of the blood
* Blood pressure
* Carbon dioxide concentration

What is the standard pathway of homeostasis?

Stimulus --> receptor --> communication pathway --> effector --> response

What are Sensory Receptors?

They detect changes in the stimuli & send a message to an effector

What is the Communication System?

Transmits a message from the receptor cells to the effector cells via a coordination centre

What are Effector Cells?

Cells that bring about a response

What is Negative Feedback?

The mechanism that brings the condition back towards the optimum

What are the stages of Negative Feedback?

1. When conditions change, the receptors detect this stimulus & send an input to the coordination centre
2. The coordination centre sends an output to the effectors & the effectors respond to the output
3. The effectors bring about a change that reverses the initial change in conditions, this causes the system to move closer to the optimum & the stimulus is reduced
4. The receptors detect a reduction in the stimulus & reduce the input to the coordination centre
5. The output from the coordination centre to the effectors is also reduced so the effectors reduce their activity
6. As the system gets closer to the optimum, the response is reduced

What is Positive Feedback?

The response that is to increase the original change

Usually harmful as it destabilises the system but can be beneficial as it stimulated an increase

What is an Endotherm?

Organisms that control their body temperature within very strict limits

They use a variety of mechanisms to control body temperature & are largely independent of external temperatures

What is an Ectotherm?

Organisms that are not able to control their body temperature as effectively as endotherms

They rely on external sources of heat & their body temperature fluctuates with the external temperatures

How do ectotherms get heat?

* Move into a sunny area
* Lie on a warm surface
* Expose a larger surface area to the sun

How do ectotherms cool down?

* Move out of the sun
* Move underground
* Reduce the surface area exposed to the sun

What are the advantages of ectothermy?

✅ Less of their food is used in respiration

✅ More energy can be converted to growth

✅ They need less food so can survive longer without food

What are the disadvantages of ectothermy?

❌ Less active in cooler temperatures

❌ Unable to escape predators in cooler temperatures

❌ Can not take advantage of food available when cold

What organ is most involved in the physiological responses to control body temperature?

Skin

What does the skin do to cool the body down?

* Sweat glands secrete fluid onto the skin surface
* Hairs & Feathers lie flat to reduce insulation
* Vasodilation of arterioles & precapillary sphincters

What does the skin do to cool the body down?

* Secrete. less sweat
* Hairs & Feathers stand erect to trap air which insulates the body
* Vasoconstriction of arterioles & precapillary sphincters

How does the Gaseous Exchange System help control body temperature?

When too hot, increased panting to remove water from the surface of the lungs & airways

How does the Liver help control body temperature?

When too cold, increased respiration means more energy is converted

How do the Skeletal Muscles help control body temperature?

When too cold, spontaneous muscle contractions (shivering) releases heat

What are the advantages of endothermy?

✅ Maintain a fairly constant body temperature

✅ Remain active even when temperatures are low

✅ Inhabit colder parts of the planet

What are the disadvantages of endothermy?

❌ Need more food

❌ Less energy from food can be used for growth

❌ May overheat in hot weather

What are the stages in the control of temperature regulation?

1. When the core temperature of the body changes, the temperature of the blood also does
2. Temperature receptors in the hypothalamus of the brain detect this change
3. The hypothalamus send out an impulse that causes different responses to reverse the change
4. Depending on the speed needed for the response, the impulse will either travel via the neuronal system (rapid) or the hormonal system (long-term)

What is the role of the Thermoregulatory Centre?

Monitors blood temperature & detects changes in the core body temperature

What is the role of Peripheral Temperature Receptors?

In the skin & monitor the temperature in the extremities

Sends information to the thermoregulatory centre