Flashcards in Homeostasis Deck (18):
a process in which an optimal internal condition is maintained
- this process requires integration of all organ systems
which systems control homeostasis? (2)
nervous and endocrine
why is maintaining internal conditions important?
The body has a narrow range in which they can work effectively (homeostatic plateau), failure of homeostasis therefore leads to pathology
Explain the principles behind negative feedback
receptors respond to a change in environment (stimulus) --> information sent to integration centre --> level checked against reference level --> diffrence in level cuases a change to be sent to an effector --> change in conditions is counteracted
- THIS IS SELF-LIMITING
Explain what is meant by a feed forward system
additional receptors allow the body to anticipate change and stimulate a response before the change occurs
Explain positive feedback
positive feedback aims to amplify the disturbance to create a greater deviation from the norm value
what is physiology?
it is the study of how the body works normally with all systems working optimally
what are the three different body fluid compartments?
- intracellular fluid
- interstitial fluid (ECF)
- plasma (ECF)
what proportion of total body water does each fluid compartment contain?
intracellular fluid = 2/3 (66%)
extracellular fluid = 1/3 (33%)
explain the nature of the barriers which separate the body compartments?
- water can move freely between all 3 compartments
- ions cannot move freely across the cell membarne
- plasma proteins cannot move across the capillary walls
THIS IS IMPORTANT AS IT ALLOWS ELECTROCHEMICAL GRADIENTS TO BE MAINTAINED
define the dilution principle
volume (v) = mass (m) / concentration (c)
what are the criteria for substances used to measure fluid compartment volume (5)
- evenly distributed in the compartment
- must not affect the distribution of water
- must be unchnaged by the body
- must be easy to meausre
*note only plasma can be sampled
name a substance that can be used to meausre plasma volume
radioactive dyes attached to plasma proteins
name a substance that can be used to measure extracellular fluid volume
- *any other substance that can cross capillary walls but not cell membranes
name a substance that can be used to measure total body water
can intracellular fluid and interstitial fluid be measured directly?
- interstital fluid volume = ECF - plasma volume
- intracellular fluid volume = total body water - ECF
how is the volume of distribution calculated?
volume = amount/mass injected (minus any excreted or metabolised) / concentration in fluid sample