homeostasis Flashcards
What is the equation of life?
Nutrients + O2 = energy (usually ATP) + CO2 + waste products
What is the goal of all body systems working together?
To bring in nutrients and eliminate waste. This creates an optimal internal environment in which all cells can function.
What are the 2 main activities of cells?
1) those that keep that actual cell alive such as protein synthesis 2) those that contribute to survival of the whole organism
What is ECF made from?
Plasma (20%) and ISF (80%)
What is the dynamic component of ECF and what is its function?
Plasma. In capillaries, it exchanges CO2 and waste with ISF as blood passes through capillaries of the body.
Which movements occur across capillary walls?
There is free movements except plasma proteins which are too large. These are restricted to the capillaries. ECF is homogenous excluding plasma proteins.
What happens when there is a failure of capillary perfusion?
Gangrene occurs.
How is water distributed in the body?
1/3 ECF and 2/3 ICF.
What % of the body is water?
Around 60%
Do males or females carry less water and why?
Females as they have more fat. Fat is 10% water and muscle is 70%. Older people also carry less water.
What is the definition of homeostasis?
Maintenance of constant conditions in the internal environment of an organism.
What is the homeostatic plateau?
A range at which the internal environment can be maintained across.
What is the upper temperature limit to life?
The temperature at which proteins are denatured.
What is the advantage of homeothermy?
Body temperature can be kept constant at 37 degrees over a range of external temperatures. However, this has a high energy cost.
What is the overall outcome of homeostasis?
Internal conditions are regulated independently of the internal environment.
Describe negative feedback.
Magnitude of controlled variable is sensed as a stimulus to a receptor. Fed to an integrating system which is compared to a reference level. Any difference between actual level and reference level generates an error signal which is fed as an effector mechanism.
In negative feedback, what is the factor that decides how big a response will be?
The magnitude of the error is proportional to the size of the response and deviation.
What adaptations occur on exposure to hot/cold?
Hot - decreased heat production and increased heat loss. Increased blood flow to skin and heal loss by sweating/evaporation. Cold - increased heat production by shivering and minimised heat loss by shutting down blood flow to the skin. Also behavioral measures.
What are the 2 main characteristics of negative feedback systems?
1) they can restore the regulated variable after its initial displacement, but cannot prevent this happening, 2) there is oscillation around the set point
What is feed-forward control?
A more sophisticated version of negative-feedback. Receptors permit the system to anticipate change and therefore activate the response earlier.
What is positive feedback?
Initial disturbance leads to a chain of events that lead to an even greater disturbance. Common in pathophysiology.
Give 1 physiological example of a positive feedback system.
Action potentials
Which processes regulate water input and output?
Input - thirst mechanism. Output - urinary losses.
What is the dilution principle?
c = m/v therefore v = m/c, from this can calculate the volume of distribution.
