Communication Systems

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Conditions that cells require to work properly:

temperature

pH

humidity

water

concentration (of enzyme/substrate)

cofactors and prosthetic groups

inhibitors

aqueous environment - keeps the substrate and products in solution

freedom from toxins

Stimulus: is any change in the environment that causes a response

E.g.: External - temperature, pH, salinity. length of day, sunlight

Internal - temperature, toxins in blood, blood glucose levels

Response: a change in behaviour or physiology as a result of a change in the environment

E.g. sweating, shivering

Hibernating due to food shortage

Horse loses its coat due to increase in temperature

Rapid change: bright light to dim light - pupil size

A good communication system is required to ensure that these different parts of the body work together effectively.

A good communication system will:

cover the whole organism

enable cells to communicate with each other

enable specific communication (target cells)

enable sufficiently rapid communication

enable both short term and long term responses

Cell Signalling

Two major systems of communication that work by cell signalling:

neuronal system - usually rapid

hormonal system - enables long term responses

Once cells have received an external signal (stimulus) there will be a sequence of changes inside the cell, involving enzymes, leading to a change (response).

Homeostasis

Conditions that need to be kept constant:

body temperature

blood glucose concentration

blood salt concentration

water potential of blood

blood pressure

carbon dioxide concentratin

Negative Feedback

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

Receptors - temperature, pH, pressure

Effectors - muscle tissue or glands

Communication pathway - nervous tissue, endocrine tissue (glands) and circulatory system (coordination centres in CNS)

Coordination involves comparing the input from the receptor with a set value to determine whether or not a response is required.

Positive Feedback

Less common

Optimum condition -> change away from optimum -> receptor detects change -> communication system informs effector -> effector reacts to increase change -> change away from optimum (repeats)

E.g.

As the cervix begins to stretch the change is signalled to the anterior pituitary gland, stimulating it to secrete the hormone oxytocin. Oxytocin increases the uterine contractions, which stretch the cervix more, which causes more secretion of oxytocin.

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