F214: Communication And Homeostasis Flashcards Preview

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Flashcards in F214: Communication And Homeostasis Deck (99)
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What is a stimulus?

Any change in the environment that causes a response.


What is a response?

Any change in behaviour or physiology as a result of a change in the environment.


Why is a multicellular organism more efficient than a single celled organism?

It's cells can be differentiated and have specific jobs it's adapted for.


What does a good communication system do?

Cover the whole body.
Enable cells to communicate with each other.
Enable specific communication.
Enable rapid communication.
Enable both short an long term responses.


What are the two systems if communication in cell signalling?

Neuronal system:
Interconnected network of neurones that signal across synapse junctions. Very quick response.

Hormonal system:
Uses the blood.
Cells in an endocrine organ release hormones directly into the blood, which is carried over the body, but is only recognised by target cells.
Long term responses.


What is homeostasis?

The maintenance of the internal environment in a constant state despite external changes.


What are example of condition that must be maintained in the body?

Blood glucose concentration.
Blood salt concentration.
Water potential of the blood.
Blood pressure.
CO2 concentration.


What is the general process of maintaining a constant environment.

A change must be detected.
The change must be signalled to other cells.
A response to reverse the change must occur.

(Negative feedback)


What is negative feedback?

A process that brings about the reversal of any change in conditions.
Ensures an optimum state is maintained, any change in the internal environment is returned to it's original state.
It is essential for homeostasis.


What structures are needed for negative feedback to work?

Sensory receptors: internal monitors that send a message to other cells when a change is detected.
eg temperature receptors or glucose conc receptors.

A communication system: nervous or hormone system. They are used to transmit messages from receptor cells to effector cells.

Effector cells: bring about a response that reverses the change detected by the receptor cells.
Eg liver or muscles cells.


What is positive feedback?

A process that increases any change detected by the receptors.
It is harmful and does not lead to homeostasis.


Describe beneficial accounts of positive feedback.

At the end of pregnancy, positive feedback brings about the dilation of the cervix.
As it begins to stretch the change is signalled to the anterior pituitary gland, stimulating it to produce oxytocin.
Oxytocin increases the contractions, which increases the secretion of more oxytocin.


What is an ectotherm?

An organism that relies on external sources of heat to regulate it body temperature.


What are advantages of being an ectotherm?

Use less energy and food in respiration.
Need to find less food so can survive for longer without it.
A greater proportion of energy is used for growth.


What are disadvantages of being an ectotherm?

They are less active in cooler temperatures, as may need to warm up in the morning before they can be active.
This increases the risk of predation.

May never be capable of activity during the winter as they never warm up sufficiently.
Thus they must have stores of energy to survive without eating.


How do ectotherms respond to temperature changes?

If it is too cold it will move to decrease absorption of heat an increase heat loss to the environment.

If it is too hot it will increase absorption of heat from the environment, eg basking in the sun.


Give examples of ectotherms regulating their body temperature.

Exposing body to the sun.
Orientating body to/from the sun.
Hide in burrow.
Alter body shape.
Increase breathing movements to evaporate more water.


What is an endotherm?

An organism that can use internal sources of heat to maintain it's body temperature.


What are advantages of endothermy?

Regardless of external temperature a constant body temperature is maintained.
Activity is possible when external temperature are cold.
Ability to inhabit colder parts of the planet.


What are the disadvantages of endothermy?

A significant part of energy intake is used to maintain body temperature.
More food required.
Less of the energy from food is used for growth, so more good a needed for growth.


Describe physiological mechanisms to maintain body temperature in endotherms.

Peripheral skin thermite rotors are stimulated by a decrease in external temp.

Vasoconstriction of arterioles to reduce heat loss by conduction.

Increased respiration to generate heat energy.

Release of adrenaline.

Shivering to generate heat energy.

Erector pulli muscles raise hair to trap air and hear.

Swearing or panting is reduced.


Where is the temperature of the blood monitored?



If the core temperature is too low how does the hypothalamus respond?

Increased rate of metabolism to release more heat from exergonic reactions.
Extra muscular contraction releases heat.
Decreases loss of heat to environment.

Vice versa for increase in temp.
Negative feedback.


What are the peripheral temperature teceptors?

In the skin and alert the hypothalamus that the extremities, eg fingers, are changing in temperature and to initiate behavioural mechanism to maintain body temperature.


What are exergonic reactions?

Release energy in the form of heat.


What is a generator potential?

A small depolarisation caused by sodium ions entering the cell.


What I an action potential?

Achieved when the membrane is depolarised to a value of about +40mv.
All or nothing.
Membrane depolarised and reaches a threshold level, then lots of sodium ions enter the axon and an action potential is reached.


What are sensory receptors?

Specialised cells that can detect changes in our surroundings.
They are transducers, they convert one form of energy to another.


What are neurones?

Nerve cells.


What do nerve cell membranes transport in and out of the cell?
How does this affect the cell?

3 Sodium ions out of the cell.
2 Potassium ions into the cell.

More sodium out than potassium in.
Polarises the cell membrane as inside is negatively charged.