Communication & Homeostasis (PT1). BIO

• suitable temperature
• suitable pH
• an aqueous environment that keeps the substrates and products in solution
• freedom from toxins and excess inhibitors

Becuase cellular activities rely on action of enzymes

• A stimulus is any change in the environment that causes a response.
• A response is a change in behaviour or physiology as a result of a change in the environment.

• External (eg. outside temp)
• Internal (eg. CO2 conc in tissue fluid - too much could disrup action of enzymes by changing pH of environment around cell)

• blood
• wastes
• substances

• Different cells (parts of body) are specialised to perform particular functions - forming tissues and organs.
• The cells that monitor blood may be well away from cells that release substances into blood or take away substances.

• cover the whole body
• enable cells to communicate with each other
• enable specific communication
• enable rapid communication
• enable both short-term and long-term responses

Cells communicate with each other by this process, in which one cell release a chemical that is detected by another cell. The target cell will respond to the signal.

• The neuronal system - neurons signal each other across synapse junctions. Very quick signal and responses.
• The hormonal system - uses blood to transport its signals. Cells in endocrine organ release hormone into blood. Allows longer-term responses to be co-ordinated.

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

• body temp
• blood glucose conc
• blood salt conc
• water potential of blood
• blood pressure
• CO2 conc

Process that brings about a reversal of any change in conditions. It ensures that an optimum steady state can be maintained, as the internal environment is returned to its original set of conditions after any change. It is essential for homeostasis.

• 2. Receptor
• 3. Communication pathway (cell signalling)
• 4. Effector

• Sensory receptors - eg. temp receptors or glucose conc receptors. Once they detect, they will be stimulated to send a message.
• Communication system - eg. nervous or endocrine. From receptor to effector. May or may not pass through coordination centre like brain.
• Effector cells - eg. liver or muscle cells.

A process that increases any change detected by the receptors. It tends to be harmful and does not lead to homeostasis (although there are examples where it is helpful).

• Harmful: when body gets too cold, enzymes become less active, then less exergonic reactions that release heat. Body cools even further.
• Beneficial: at end of pregnancy, to bring about dilation of cervic. As cervix stretches, the change is signalled to anterior pituitary gland, stimulating it to secrete hormone, oxytocin. This allows more stretch. (ALSO, Anitgen production?)

• Changes in temp have effect on structure of proteins, eg. enzymes.
• Enzyme structure is very specific to its function, and so temp can greatly affect activity of enzymes and hence organism's ability to be active and survive.

• An organism that relies on external sources of heat to regulate its body temperature.
• (Not able to increase respiration rate to generate heat internally).

• Use less food in respiration.
• Need to find less food and may survive for long periods without eating. eg. snakes can for several weeks.
• Greater proportion of energy fro food can be used for growth.

• Less active in cooler temps - puts them at greater risk of predation. And need to sunbathe etc.
• May not be capable of activity during winter, as they never warm up sufficiently. Means they must have sufficient stores of energy over winter without eating.

• Expose body to sun
• Hide in shade
• Alter body shape
• Increase breathing movements.

An organism that can use internal sources of heat, such as heat generated from metabolism in the liver, to maintain its body temperature.

• Exergonic
• Endotherms can increase rate of respiration in liver (exergonic reaction) simply to release heat.

• Fairly constant body temp (within a narrow range) whatever the temp is externaly.
• Activity (enzymes) possible when external temp are cool. (eg. night, winter)
• Ability to inhibit colder parts of planet (Larger range of habitats).
• No need to bathe in sun - less predation.

• Significant part of energy intake used to maintain body temp in cold.
• Therefore, more food recquired.
• Less energy from food is used for growth/more food needed for growth.

• Sweat glands in skin (evaporation of water etc)
• Lungs, mouth and nose (evaporation of water from these surfaces)
• Hairs on skin (insulation)
• Arterioles leading to capillaries in skin [Vasodilation - sphincters open; Vasoconstriction - sphincters close] regulates heat being radiated from skin
• Liver cells - rate of metabolism
• Skeletal muscles - spontaneous contractions (shivering) generate heat as muscle cells respire more.

• Thermoregulatory centre in hypothalamus (monitor changes in temp in blood)
• Nervous system and hormonal system carry signals to...
• skin, liver and muscles

These in the skin monitor the temp in the extremities. These give an early warning to the thermoregultory centre in hypothalamus, on whether the external environment is very cold or hot. The brain can then initiate behavioural mechanisms, enabling it to respons quickly and avoid too much variation in core body temp.

• Surface-area-to-volume ratio.
• A smaller surface-area-to-volume ratio, like elephants, lose smaller proportion of body heat than those with larger S-A-T-V ratios, like a rat.