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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)


acclimatization to hot weather

takes 1-6 weeks
-sweating capabilities increase from 1 L/hr to 2-3 L/hr


sweat gland innervations

acetylcholine-secreting sympathetic nerve
-primary PRO-free secretion formed by glandular portion
-absorbtion in duct, leaving dilute, watery secretion
-if rate of sweating is too high, will not reabsorb


cold VS warmth receptor fibers in skin

10X more cold receptors than warm, b/c more sensitive to cold (to prevent hypothermia)
-both project to control center in hypothalamus


cold VS warmth sensitive neurons in hypothalamjus

more heat-sensitive neurons
-integrates thermal information from skin and central temperature receptors


effects of increased body temperature

skin vasodilation, sweating, decreased heat production


effects of decreased body temperature

skin vasoconstriction, piloerection, thermogenesis (heat production), (nor)epinephrine excitation


effects of heating preoptic area of hypothalamus

heat-sensitive neurons and receptors in hypothalamus are activated
-skin sweats profusely and skin vessels vasodilate


components of negative feedback homeostatic reflex arc in thermoregulation

regulated variable - body temperature
stimulus - decreased body temperature
sensors - temperature-sensitive neurons in periphery and CNS
integrator - hypothalamic neurons that compare input to set point
effectors - sympathetic nerves regulating blood vessels in skin/sweat glands
-hypothalamic motor centers regulating shivering


body heat balance during exercise (rate of heat production, core temperature, and skin temperature)

rate of heat production increases in proportion to exercise intensity, exceeding rate of heat dissipation
-causes heat storage and rise in core temp due to delayed onset of sweating (provides error signal that sustains sweating response in exercise)
-mean skin temperature is maintained nearly constant due to effect of sweating
--decreases slightly due to increased evaporative cooling of skin


pyrogen effect

trigger increase in set point of hypothalamic temperature-regulating center
-prostaglandin synthesis effect hypothalamus to increase set temperature
-after pyrogens cleared, the setpoint is reduced


effects of increasing the set point on body temperatrue

-epinephrine secretion


heat exhaustion/collapse

failure in cardiovascular homeostasis in hot environment
-decrease in circulating blood volume cauesd by skin vasodilation and sweating-induced decrease in central venous pressure
-blood pools in limbs, causing weakness, confusion, ataxia, anxiety, vertigo, headache, nausea, and finally syncope
-dilated pupils and profuse sweating
-treat with rest in cool place with fluid/electrolyte replacement
-core temperatures normal/mildly elevated



elevated core temperature and heart rate + severe neurological disturbances (loss of consciousness/convulsions; normal blood pressure)
-classical: environmental stress overwhelms impaired thermoregulatory system
-exertional: high metabolic heat production
-dry air: promotes rapid evaporative heat loss (survives for many hours)
-humid air: elevates core temperature
-treat with rapid lowering of core body temp (ice bath), hydration, airway maintenance


malignant hyperthermia

massive increase in metabolic rate, O2 consumption, and lethal heat production in skeletal muscle
-usually have mutations that disrupt Ca homeostasis in muscle (b/c mutated ryanodine receptor)
-triggered by inhalation anesthetics and depolarizing muscle relaxants
-treat with discontinuation of trigering agent, ryanodine receptor antagonists, cooling body



heat production cannot increase enough to compensate for heat loss
-drowsiness, slurred speech, bradycardia, hypoventilation
-if severe: coma, hypotension, fatal cardiac arrythmias



freezing of surface areas
-permanent necrotic damage if extensive ice crystals form in cells of skin and subcutaneous areas
-gangrene follows thawing
-sudden cold-induced vasodilation is final protective response near freezing temperatures (smooth muscle in vascular walls in paralyzed by cold)



reduction in charge separation, with less negative (more positive) membrane potential



increase in charge separation, with more negative membrane potential



amount of electrical energy separated for a given electrical potential
C = Q/V


which is more, intracellular or extracellular for:

more K+ intracellular
more Na+, Ca++ extracellular


diffusion potential

potential difference generated across a membrane when a charged solute diffuses down its concentration gradient (caused by diffusion of ions)


equilibrium potential

concentration difference for an ion across a membrane, and membrane is permeable to that ion, a diffusion potential is created


Nernst equation

equilibrium potential = (RT/zF)*ln*([X]2/[X]1)
-usually negative


Goldman equation

resting membrane potential =
58log((P[K]o + P[Na]o)/(P[K]i + P[Na]i))
where P = permeability in physical terms
(alpha = Pna/Pk)


effects of changing solute concentrations on equilibrium potential

increasing concentrations will increase from negative to near/above zero


normal ratio of K:Na:Cl at resting potential and peak of action potential

rest: 1.0 : 0.04 : 0.45
AP: 1.0 : 20 : 0.45


total body water and its proportions

60% of body weight; 42 L if 70 kg man
-ICF: 2/3 of TBW = 40% body weight = 28 L
-ECF: 1/3 of TBW = 20% body weight = 14 L
--interstitial fluid: 75% ECF = 11 L
--plasma: 25% ECF = 55% of blood volume = 3 L


osmotic pressure

amount of pressure that would have to be applied to force water back into its original chamber
-water moves down its osmotic gradient until two chambers equilibriate, but can be forced back with proper applied pressure


effect of extracellular osmolarity on intracellular volume and osmolarity

hypotonic: water enters ICF from ECF
isotonic: fluid stays in ECF
hypertonic: water enters ECF from ICF

equilibriate the osmolarity at expense of volume
osmolarity does NOT return to normal isotonic, but volume eventually does

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