Homeostasis Flashcards
Define the term homeostasis
The stable condition of the body and it’s internal environment and the maintainance or regulation to keep it in an optimum state
How does a negative feedback control system work?
A variable is monitored against a reference level, any change of the variable is sensed by a receptor which produces an effector mechanism which produces a response
What is the aim of negative feedback?
To restore the internal environment to optimal conditions
What are the two characteristics of negative feedback systems?
There is oscillation around the set point AND it restores the regulated variable after inital displacemnt BUT cannot prevent it happening
What can feed forward control do that negative feedback can’t?
Additional receptors permit the system to anticipate change and activate response earlier
What does positive feedback do?
The signal from the initial disturbance sets off a train of events that lead to an even greater disturbance
What is a feature of positive feedback?
Self-amplification
What are examples of positive feedback?
Diabetes, childbirth, nerve action potential
What percentage of body weight is water?
60%
What are the three compartments where water is found in the body?
Intracellular fluid, interstitial fluid, plasma
What makesup extracellular fluid?
Interstitial fluid and plasma
Where is 2/3s of the water found?
Intracellular fluid (ICF)
The capillary wall is permeable to everything but?
Plasma protein
What has selective permeability?
Cell membrane
What is roughly the volume of total body water?
42L
What do we have twice as much as?
Twice as much ICF as ECF
What percentage of ECF is ISF?
80%
What percentage of ECF is plasma?
20%
What is the dynamic component of the ECF?
Plasma
What freely exchanges nutrients and waste with the ISF?
Plasma
Where does plasma exchange with the ISF?
Capillaries
What is only found in plasma due to it being restricted by size?
Plasma proteins
What can be sampled when trying to determine body fluid volumes?
ONLY compartments where plasma is a component (plasma, ECF, TBW)
What can be used to measure plasma volume?
Evans blue
What can be used to measure extracellular volume (ECF)?
Something that freely crosses capillary walls but cannot cross cell membranes e.g. Insulin, sucrose or Na/Cl isotopes
What can be used to measure total body water (TBW)?
Loading dose of heavy/deuterated water
How would you measure interstitial fluid volume (ISF)?
ECF - PV
How would you measure intracellular fluid volume (ICF)?
TBW - ECF
How would you calculate volume of distribution (using dilution principle)?
Inject substance that will stay in one compartment only
Volume of distribution = amount injected - any removed by excretion or metaboism / concentration in sampled fluid
Why is the large concentration gradient between ICF and ECF necessary?
For nerve and muscle function
Where is Na+ concentration higher?
ECF
Where is K+ concentration higher?
ICF
Where is Cl- concentration higher?
ECF
