Homeostasis Flashcards
(37 cards)
Define homeostasis?
The state of steady internal physical and chemical conditions maintained by living systems.
Define cellular homeostasis?
The processes involved in the maintenance of an internal steady state at the cellular level.
Living systems are considered “open dynamic systems”, what does this mean (2)?
Not at thermodynamic equilibrium.
Continual throughput of matter and energy.
(yet remain remarkably constant in many aspects).
What is the general rule for a steady state?
Sum of inputs = sum of outputs.
(If not, ‘pool size’ rises or falls until they’re equal).
How is the relation between inputs and outputs affected by growth and development?
During growth and development, inputs>outputs.
What is an example of transient imbalances at a cellular level?
Na+ in = Na+ out.
Transient imbalance of this steady state is crucial for action potentials.
What is meant by the term “transient imbalance”?
When a state is unbalanced/unequal or varies over time.
What is an example of transient imbalance at the whole body level (3)?
H2O in = H2O out:
Varies from changes in hydration status.
Ca ions in = Ca ions out:
Except during bone growth/resorption.
O2 in = CO2 out:
Difference reflects stoichiometry of respiration.
Give an example of transient imbalance at the organ level?
Fatty acid uptake = fatty acid oxidation + triglyceride synthesis + triglyceride export:
Insulin resistance causes reduced FA oxidation in muscle/liver = fatty liver.
What is the aim of feedback pathways?
Maintenance at a particular value of the control variable in the face of perturbations.
What happens if a variable leaves its target range with reference to feedback pathways?
Sensor activated.
Feedback signal sent to effector.
Effector opposes unwanted change.
(Negative feedback loop).
What is an example of positive feedback?
Nerve action potential.
What happens, in feedback pathways, if signals are sent to the brain centre?
The brain issues neuronal/hormonal signals to effector organs.
What is the name given for failures in homeostasis (in disease)?
Decompensation.
Name the 4 types of passive transport across a membrane?
Simple diffusion:
Through lipid bilayer.
Facilitated diffusion:
Through non-specific transporter
Facilitated diffusion:
Through specific transporter.
Osmosis:
Through lipid bilayer or aquaporins.
How does the osmolality of extracellular fluid (ECF) affect cell volume?
ECF osmolality up (hypertonic) = Cell volume down.
ECF osmolality down (hypotonic) = cell volume up.
What are two ways the body can regulate extra cellular fluid (ECF) osmolality?
Control of body Na+ content:
Mainly renal Na+ handling.
Control of body water:
Thirst, sweating, renal water handling.
What are considered osmoles in cells?
Ions and metabolites.
How can osmoles be regulated in cells?
By cerebral osmoregulation.
Cellular [Ca2+] is naturally high due to negative membrane potential, how is this combatted in cells?
The energy of Na+ gradient (and ATP directly) is used to pump it out (secondary active transporters?).
What are the sensors for body temperature regulation (2)?
Hypothalamic thermoregulatory centres.
Peripheral temperature sensors.
What are effectors for the regulation of body temperature (3)?
Heat losing:
Behavioural (avoid heat).
Sweating.
Vasodilation.
Heat conserving:
Behavioural (avoid cold).
Vasoconstriction.
Heat generating:
Non-shivering thermogenesis (metabolic).
Shivering.
What occurs if body core temperature exceeds 40C?
Heat stroke leading to cerebral dysfunction.
What is hyperthermia and what are the cascading effects of it?
When heat challenge exceeds regulatory capacity.
Causes organ dysfunction due to heat which impairs regulatory mechanisms.
Results in low cardiac output.
This reduces skin blood flow, causing unwanted positive feedback.
