Flashcards in Introduction to cellular homeostasis Deck (16):
The tendency towards a relatively stable equilibrium between interdependent elements, especially as maintained by physiological processes.
Importance of homeostasis
Maintaining a constant internal chemical composition and temperature vs variable external conditions.
General homeostatic principle
Variable set point disturbed -> sensor detects disturbance -> effector action counteracts imbalance
Biological variables controlled by homeostasis
-Waste product excretion
-Extracellular fluid composition
Parameters that need to be kept in narrow range for optimal cell functon
Na+ cellular fluid concentrations
Intracellular fluid: 10-15 mmol/L
Extracellular fluid: 135-147 mmol/L
K+ cellular fluid concentrations
Intracellular fluid: 120-150 mmol/L
Extracellular fluid: 3.5-5 mmol/L
Cl- cellular fluid concentrations
Intracellular fluid: 20-30 mmol/L
Extracellular fluid: 95-105 mmol/L
HCO3- cellular fluid concentrations
Intracellular fluid: 12-16 mmol/L
Extracellular fluid: 22-28 mmol/L
Ca2+ cellular fluid concentrations
Intracellular fluid: ~10-7 mmol/L
Extracellular fluid: 1.1-1.4 mmol/L
Why are Na+ and Cl- so concentrated in extracellular fluid?
High NaCl concentration is the result of evolution from organisms living in salty sea water.
Interface between internal environment of body and external space (skin, lungs, intestines).
-> maintains constant composition and volume of ECF
-> provides stable environment for cells
How is homeostasis achieved?
Regulation of exchange of molecules/ions between both cytosol and ECF along with cytosol and intracellular compartments.
-> possible due to nature of cell membrane (phospholipid bilayer & membrane proteins)
What are phospholipid bilayers permeable to?
-small uncharged molecules
Membrane permeability coefficient
J = P x (C1-C2)
J: net rate of solute movement
P: permeability coefficient
C1, C2: concentrations on both sides of membrane