5.1 Communication and Homeostasis Flashcards
Cell signalling
This is when one cell will release a chemical that is detected by another cell. The second cell will respond to the signal released by the first cell.
(The way in which cells communicate with each other)
Effector
A cell, tissue or organ that brings about a response
Homeostasis
Maintaining a constant internal environment despite changes in external and internal factors.
Negative feedback
The mechanism that reverses the change, bringing the system back to its optimum.
e.g. rise/fall in core temperature
Positive feedback
The mechanism that increases a change, taking the system further away from the optimum.
e.g. dilation of cervix.. stimulates posterior pituitary gland to secrete hormone oxytocin, which dilates cervix etc. Birth ends production of oxytocin - BENEFICIAL
N.B. usually PF destabilises system and is harmful.
Flow diagram for mechanism of negative feedback
Conditions change away from optimum - --> detected by receptors --> sends input to coordination centre --> coordination centre sends output to the effectors --> effectors respond to output (reverses change - closer to optimum) --> eventually back to optimum condition
What 3 processes must occur for negative feedback to work?
- A change to the internal environment must be detected.
- The change must be signalled to other cells.
- There must be an effective response that reverses the change in the conditions.
What are the two major systems of communication that work by cell signalling?
Neuronal system: an interconnected network of neurones that signal to each other across synapse junctions. The neurones can conduct a signal very quickly and enable rapid responses to stimuli that may be changing quickly.
Hormonal system: a system that uses blood to transport in signals. Cells in an endocrine organ release the signal (a hormone) directly into the blood. The hormone is transported throughout the body, but is only recognised by specific target cells. The hormonal system enables longer-term responses to be coordinated.
Standard response pathway
Stimulus –> receptor –> communication pathway (cell signalling) –> effector –> response
Sensory receptors
cells/ sensory nerve endings that respond to a stimulus in the internal or external environment of an organism and can create action potentials.
Role of sensory receptor
to detect changes in the environment
Role of effector
To carry out a response
Input
Information sent from the sensory receptors to the coordination centre.
Output
Information sent by coordination centre to the effectors
Explain the difference between negative feedback and positive feedback
Negative feedback occurs where the change in conditions detected by the sensory receptors is reversed by the action of the effectors. Positive feedback occurs where the initial change in conditions is increased by the action of the effectors.
Ectotherm
An organism that relies on external sources of heat to maintain body temperature.
Endotherm
An organism that uses heat from metabolic reactions to maintain body temperature.
What would ectotherms do if they were cold?
- move into a sunny area (bask in sun)
- lie on a warm surface
- expose a larger SA to the sun
What would ectotherms do if they were hot?
- move out of sun (into shade)
- move underground
- reduce the body surface exposed to the usn
Advantages of ectothermy
- Less of their food is used in R
- More of the E and nutrients gained from food can be converted to growth.
- They need to find less food
- They can survive for long periods without food.
Disadvantages of ectothermy
- less active in cooler temperatures
- at risk from predators when they are cold as unable to escape
- cannot take advantage of food that is available when cold
Advantages of endothermy
- Can maintain a fairly constant body temperature whatever the temperature externally.
- remain active even when the external temperatures are low, which means they can take advantage of prey that may be available or escape from potential predators.
- inhabit colder parts of the planet.
Disadvantages of endothermy
- Use significant part of their E intake to maintain body temperature in the cold
- need more food
- use for growth a lower proportion of the E and nutrients gained from food
- may overheat in hot weather
Role of peripheral temperature receptors
Monitor the T in the extremities. This information is fed to the thermoregulatory centre in the hypothalamus.
–> will signal brain that external environment is either very hot or very cold ad brain can initiate behavioural mechanisms for maintaining the body temperature (e.g. moving to shade)
