Homeostasis Flashcards
What is homeostasis?
Maintenance of a relatively stable internal environment (i.e., extracellular fluid) under fluctuating environmental conditions
Steady-state Balance
A state where a particular parameter or condition remains relatively constant despite variable inputs and outputs. Steady-state balance is not “equilibrium”, which is a state of balance between opposing forces or actions (i.e., chemical reactions)
A + B «AB
Define homeostasis
maintenance of a relatively stable internal environment (i.e., extracellular fluid) under fluctuating environmental conditions
Define steady-state balance
A state where a particular parameter or condition remains relatively constant despite variable inputs and outputs
Is steady state balance the same thing as equilibrium?
No - not a state where [products] = [reactants] but rather state where things aren’t changing
What are the elements of homeostatic regulation? (3)
Established set point
Sensory input
Integration
Effector mechanisms
Describe how water balance is an example of homeostasis.
Hypothalamus monitors body fluid osmolality and can send neural signal to change intake (trigger or inhibit thirst) or can send a hormonal signal (ADH) to change excretion via kidneys.
When discussing normal volumes of fluid compartments, what should be the proportions of TBW, ICF, ECF?
TBW = 0.6 * Mass
ICF = 2/3 TBW
ECF = 1/3 TBW
(subdivided into plasma and interstitial, plasma is 1/4 of ECF volume and interstitial is 3/4 of ECF volume)
When thinking about fluid loss from the ICF or the ECF, how does the body tend to maintain the ECF?
The body maintains a constant ECF volume (and composition), which then determines the volume (and composition) of the ICF via membrane transport proteins.
Describe how the ECF and ICF differ in composition.
ECF
- High [Na+]
- Low [K+]
- More glucose than ICF
- High [Ca2+]
ICF
- Low [Na+]
- High [K+]
- Less glucose
- Low Ca2+ (stored in sarcoplasmic reticulum)
What are some parameters for which the body maintains homeostatic set points?
Volume, composition (concentration), temperature
What is positive and negative balance? What does it mean for living organisms?
Positive: Input > Output
Negative: Input < Output
Not compatible with life except for very transient periods
What are some examples of sensors of homeostasis?
Cells in different parts of body, CNS, endocrine, renal
What are starling forces?
Forces that govern the rate and direction of fluid flow in capillaries. Determined by the hydrostatic pressure (pressure exerted by fluid) and oncotic pressure (pressure exerted by proteins in blood)
Why do membrane transporters play an important role in homeostasis?
Because they allow substances to pass between the different body compartments and thus they are essential for maintaining homeostasis
