Homeostasis Flashcards
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)
- H+
- H/K
- Ca++
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)
radiation
transfers heat as electromagnetic waves between objects not in contact
- rate of transfer proportional to temperature difference
- humans emit infrared (~60%)
conduction
intermolecular thermal heat transfer between solid objects in direct contact
-minimal if wearing shoes/clothing
convection
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
evaporation
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
chills:
- vasoconstriction
- piloerection
- epinephrine secretion
- shivering
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
heatstroke
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
hypothermia
heat production cannot increase enough to compensate for heat loss
- drowsiness, slurred speech, bradycardia, hypoventilation
- if severe: coma, hypotension, fatal cardiac arrythmias
frostbite
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)
depolarization
reduction in charge separation, with less negative (more positive) membrane potential
hyperpolarization
increase in charge separation, with more negative membrane potential
capitance
amount of electrical energy separated for a given electrical potential
C = Q/V
which is more, intracellular or extracellular for:
- K+
- Na+
- Ca++
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)
=(58/z)log([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
