stress and hormones Flashcards
review of transcription and genetic translation
- to synthesize mRNA, the two strands of DNA must be unraveled by enzymes called HELICASES
- gene consists of unique linear sequence of DNA (special marker sequences denote the start/end points of each gene)
- PROMOTER/FACILITATORY region marks the start of the gene
- binding of a TRANSCRIPTION factor to promoter allows enzyme RNA POLYMERASE to attach to promoter and begin process of DNA SYNTHESIS
- sequence of RNA nucleotides (determined by sequence of nucleotides along the DNA) eventually determines sequence of AMINO ACIDS in the PROTEIN product of the gene
- DNA METHYLATION and HISTONE MODIFICATION are EPIGENETIC processes
- DNA methylation is a process of LONG-TERM GENE SILENCING that involves adding a methyl group to cytosines in the promoter version of a gene
transcription versus translation
- transcription:
converts DNA into mRNA - translation:
decodes mRNA into amino acids, forming proteins essential for life functions
helicases
the enzymes that unravel the two strands of DNA
because DNA must be unraveled in order for it to be synthesized
genes consist of unique…
linear sequences of DNA
what marks the start of a gene?
promoter/facilitatory region
binding of what to the promoter allows RNA polymerase to attach and begin RNA synthesis?
transcription factor
what determines the sequence of amino acids in the protein product of the gene?
the sequence of RNA nucleotides
which is in turn determined by the sequence of nucleotides along the DNA
DNA methylation and histone modification are what kind of processes?
epigenetic
DNA methylation
process of long-term gene silencing
involves attaching a methyl group to cytosines in the promoter region of a gene
percentage of acute myocardial infractions (AMIs - heart attacks) are associated by patients to specific stress triggers?
48%
wars, natural disasters, anxiety-provoking events are associated with increase in heart attack rates
4 main questions in the behavioural endocrinology of stress
- why are some groups/individuals affected more severely by a potentially stressful event than others?
- are there differences among individuals in perception of stressors, perturbations to homeostasis, and physiological, psychological and behavioural responses to stressors?
- are stress responses always detrimental, or can they be adaptive in some circumstances?
- how can we measure stress?
homeostasis
the ability to maintain optimal conditions in the body
hormones are critical in this process
homeostasis involves the regulation of…
fluid and sodium balance
energy balance
eating
body mass and temperature regulation
stressors and homeostasis
stressors typically disrupt homeostasis
this affects the brain and behaviour
important to note: brain itself can perceive psychological factors as stressful and evoke a stress response
3 main sources of stressors
- environmental factors:
temperature extremes, noises - physiological factors:
insufficient food quality/quantity, water deprivation - psychosocial factors:
maltreatment, social subordination, novel situations, lack of control
stress
any significant disturbance of homeostasis
ie. extreme temperatures, psychological factors
stressor
condition, agent or other stimulus that causes stress in an organism
stress-response
suite of physiological and behavioural responses that help to re-establish homeostasis
flight or flight response
automatic and endocrine responses that prepare an individual to battle or flee from real or perceived threat, attack or harm
examples of systems involved in mediation of stressors
glucocorticoids
sympathetic/parasympathetic transmitters
cytokines
metabolic hormones
systems that mediate stress operate as a nonlinear….
nonlinear, interactive network in which mediators UP and DOWN-REGULATE one another
depending on factors like:
1. concentration
2. location in the body
3. sequential and temporal patterning
two systems that constitute the major components of the stress response
- system involving epinephrine/adrenaline
- from adrenal medulla - system involving norepineprhine/noradrenaline
- from adrenal cortex
emergency theory
within seconds of perceiving a stressor:
- sympathetic NS begins to secrete norepinephrine
- adrenal medullae begin to secrete epinephrine
immediate and non-specific component
involved in changes in:
a) cardiovascular tone
b) respiration rate
c) blood flow to muscles from trunk that support fight or flight behaviours
modern perspectives on stress = less likely to focus on fight or flight than on…
psychological features of stress
namely the degree of control the stressed individual has over the situation
exam: epinephrine and norepinephrine levels
epinephrine and norepinephrine levels increase and peak on the day of the exam
and then fall afterwards
parachute jump: hormone levels
cortisol, growth hormone and epinephrine all increase at the time of the jump
testosterone drops though
Hans Selye (1930s) is considered the…
founder of modern stress research
he was the first to observe epinephrine and glucocorticoid release in response to virtually any stressor (shows that stress response is NON-SPECIFIC)
common endocrine event underlying very different stress responses is…
release of glucocorticoids from adrenal cortex
caused by stressors as diverse as frostbite, formaldehyde exposure, hemorrhage
the two primary “stress hormones”
epinephrine and cortisol
despite facts that:
- their major endocrine functions involve metabolism
- circadian variation in these hormones occurs even in absence to stress exposure
both rats with ovarian hormone injection AND saline injection…
developed peptic ulcers, adrenal hypertrophy, regression of immune organs
was probably the handling of the animals in the lab that was causing them stress - not the injections
prolonged stress response - the _______ _______ syndrome
general adaptation syndrome
general adaptation syndrome consists of 3 stages…
- alarm reaction stage
- stage of resistance
- stage of exhaustion
alarm reaction stage
initial phase of body’s response to stress
stressor is perceived - body activates fight or flight response
^involves release of stress hormones (epinephrine, cortisol)
physiological changes occur rapidly (increased heart rate, heightened awareness, mobilization of energy reserves)
all to prepare the body to cope with the stressor
stage of resistance
if stressor persists beyond initial alarm reaction stage…
body enters stage of resistance
during this phase, body tries to adapt to ongoing stressor
by maintaining elevated levels of hormones and physiological responses
body tries to cope with stressor and restore homeostasis
stage of exhaustion
if stressor persists for extended period of time OR if body’s resources become depleted…
stage of exhaustion occurs
body’s ability to cope with stressor diminishes
physiological resources are depleted
Chrousos definition of stress
“the recognition by the body of a stressor and therefore, the state of heightened homeostasis. this way the stressors are threats against homeostasis; and adaptive responses are the body’s attempt to counteract the stressor and reestablish homeostasis”
Sapolsky definition of stress
“anything that throws your body out of homeostatic balance. considered together, stress is the sum of all nonspecific effects of factors that can act on the body to increase energy consumption above some resting, or basal, level.
in the short term, the stress response is adaptive and helps individuals cope with emergency situations; in the long term, the stress response tends to be maladaptive”
3 limits to the homeostatic concept of stress
- doesn’t address issue that PSYCHOLOGICAL stressors can evoke a full stress response; this psychological stress response actually causes HOMEOSTATIC IMBALANCE in an individual, rather than restoring it
- doesn’t account for INDIVIDUAL VARIATION in perception of stressors
- for a definition of stress to be useful, must address how the SAME STIMULUS can be STRESSFUL to one individual and PLEASURABLE to another
stress is a condition in which individuals are aroused by…
aversive stimuli
for an event to be defined as stressful, the individual must…
perceive it as aversive
a stressful event involves an individual’s lack of…
perception of control over the aversive stimuli
predictive homeostasis
the response range that comprises daily and seasonal variation in a given hormone
reactive homeostasis
range of mediator fluctuations necessary to respond to threats
allostasis
homeostatic overload
values above the reactive homeostasis range
allostatic load/overload
homeostatic failure
mediator values below the predictive homeostasis range
allostatic load/overload
physiological effects of stress response: within seconds…
- sympathetic NS secretes norepinephrine and epinephrine
from adrenal medulla
physiological effects of stress response: after release of epinephrine and norepinephrine…
HPA axis: hypothalamus releases cortico-tropin releasing hormone
this stimulates release of adrenocorticotropin hormone from anterior pituitary gland
within minutes, adrenal cortex begins to secrete glucocorticoids
3 main events of hormone release immediately after stressor presentation
- sympathetic NS (adrenal medulla) releases norepinephrine and epinephrine
- hypothalamus releases corticotropin-releasing hormone - stimulates release of adrenocorticotropin hormone from anterior pituitary
- adrenal cortex begins to secrete glucocorticoids
other hormones secreted from endocrine tissues during a stress response
prolactin
urocortin
glucagon
thyroid hormones
vasopressin
