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Flashcards in Homeostasis Deck (59)
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steady state VS chemical equilibrium

steady state - needs energy input; the amount of substance in compartments don't change over time (still movement in/out)
-potential is a resting membrane potential
chemical equilibrium - doesn't need energy input


mass balance for a system at steady state for metabolism

any substance taken in by the body is nearly equal to the amount leaving the body plus that removed by metabolism


basal metabolic rate

energy expenditure at rest; largest proportion of our daily energy usage (60% if sedentary)
-less than RMR b/c various forms of daily activity


resting metabolic rate

more than BMR b/c of various forms of daily activity
-higher in males, some hormones, if arctic, younger age


electrolyte concentration in extracellular and intracellular fluid

ECF - Na+
ICF - K+
maintained by Na+/K+ ATPases (3 Na+ out, 2 K+ in)


what is the major process used to maintain homeostasis

negative feedback
-initiation of responses that counter deviations iof a controlled variable from a normal range
-acts in combination with feedforward controls


feedforward controls

regulates body systems, particularly when a change with time is desirable
-acts in combination with negative feedback
-involves a command signal, but doesn't directly affect the sensed compound


positive feedback

accelerates a process and can be unstable
-less common in nature than negative feedback, but still important


perturbation, gain, and correction

P - original change in homeostasis (ex: drop in blood pressure)
C - how much of the pertubation is repaired (pertubation - remaining error)
G - correction/remaining error (capacity of the system to restore a controlled variable to its set point after a pertubation)


negative and positive feedback due to blood loss

NFB: if less than 1 liter of blood lost; eventually returns to homeostasis
PFB: if more than 1 liter of blood lost; will eventually die


thermodynamic equilibrium in absence of solute electrochemical potential difference across membrane

driving force for solute transport
-charged: if equal and opposite in direction across membrane, net force is zero
-uncharged: if equal and opposite in direction, NOT a driving force


3D concept of a gradient

difference - solute concentration
direction - "up/against" or "down" gradient
driving force - potential energy acting on movement or change in physical and/or chemical properties of a defined space relative to comparable space


types of thermodynamic transport

passive transport - only down gradient
primary active transport - only up gradient, needs energy
secondary active transport - dependent on PAT to create a gradient (indirectly uses energy)
-sometimes travels up gradient, other times down gradient


types of molecular mechanisms

ion translocating pump (primary active)
channel (passive; mostly inorganic ions)
carriers (passive uniporters, secondary active symporters/cotransporters, or antiporders/cotransporter/exchangers)


ion-translocating ATPases

primary active transporters
-Na/K (3 Na out, 2 K in)


kinetics of simple diffusion VS carrier-mediated diffusion

SD: straight line that doesn't "saturate"
CM: hyperbolic curve that "saturates"


transfer stoicheometry

number of substrate molecules transported in one complete cycle of molecular events mediated by transport PRO, resulting in transfer of substrate across membrane


transfer electrogenicity

confers membrane potential difference (voltage) as well as substrate concentration difference as an additional driving force favoring/opposing transfer


acid extruder VS acid loader

Extruder: H+ leaves, base enters, increasing pH (acidosis: H+ is expelled in exchange for Na+)
Loaders: H+ enters, base exits, decreasing pH (alkalosis: HCO3 is expelled in exchange for Cl-)


what do core temperatures vary with?

time of day (highest between 3-6 PM, lowest between 3-6 AM)
stage of mestrual cycle (1 C higher if post-ovulatory)
level of activity/emotional stress
age (decreases as older)



transfers heat as electromagnetic waves between objects not in contact
-rate of transfer proportional to temperature difference
-humans emit infrared (~60%)



intermolecular thermal heat transfer between solid objects in direct contact
-minimal if wearing shoes/clothing



loss/gain of heat by movement of air/water over the body
-heat rises, carrying heat away from body
-body immersed in water exchanges most heat by convection



from skin and respriatory tract, carrying large amounts of heat generated by body (when air temp higher than body temp)
-air circulation and hypotonic improves rate of evaporation
-high humidity makes it less effective


where is most body heat generated?

deep organs, by cellular metabolism


what determines rate of heat loss

how rapidly heat is:
1. carried from core to skin
2. transferred from skin to surroundings
regulated by sympathetic nervous system (increased efferent will decrease blood flow to skin)


passive/unregulated heat transfer

in steady state, rate of heat production by body core must be matched by flow of heat from core to the skin to environment


continuous venous plexus

blood vessels beneath skin, very profuse
-supplied by skin capillaries and arteriovenous anastomosis


how large is the increase in heat conductace from vasoconstricted to vasodilated

8-fold from changes in environmental temperatures


sympathetic nervous system in regards to temperature changes

increased temp: inhibits supply to skin so vasodilation (improved heat loss)
decreased temp: activates supply so vasoconstricts (improved heat retention)

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