Homeostasis refers to a stable internal state despite external changes, while allostasis addresses the complex regulatory processes needed to maintain homeostasis given varying environmental demands. The general adaptation syndrome describes the body's three-stage response to stressors - alarm, resistance, and exhaustion - with the goal of allostatic regulation to restore homeostasis. However, excessive or prolonged stress can lead to allostatic overload, undermining the body's ability to maintain homeostasis and potentially resulting in pathophysiological consequences.

1. HOMEOSTASIS AND ADAPTIVE
RESPONSES TO STRESSORS
Chapter 2
1

2. HOMEOSTASIS AND ALLOSTASIS
• Homeostasis: a state in which all symptoms
are in balance at an ideal “set point” despite
alterations within the body
• Homeostatic response: mechanistic,
predictable series of orchestrated internal
events
2

3. HOMEOSTASIS AND ALLOSTASIS
(CONT.)
• Allostasis: addresses complexities and
variable levels of activity necessary to
maintain or re-establish homeostasis
• Carried out by a superordinate set of systems
that support homeostasis in light of
environmental and lifestyle changes
3

4. STRESS AS A CONCEPT
• Stress: physical, chemical, or emotional factor
resulting in tension of body or mind
• Or an actual state that tension produces
4

5. GENERAL ADAPTATION
SYNDROME AND ALLOSTASIS
General Adaptation Syndrome (GAS) (Selye)
• Alarm reaction: fight-or-flight response due to
stressful stimulus
• Allostatic state: Refers to the activity of various
systems in attempting to restore homeostasis
• Stage of resistance: The activity of the
nervous and endocrine systems in returning
the body to homeostasis
5

6. GENERAL ADAPTATION
SYNDROME AND ALLOSTASIS
(CONT.)
6

7. GENERAL ADAPTATION
SYNDROME AND ALLOSTASIS
(CONT.)
7

8. • Stage of exhaustion: point where body can
no longer return to homeostasis
• Allostatic overload: “cost” of body’s organs and
tissues for an excessive or ineffectively regulated
allostatic response
General Adaptation Syndrome and
Allostasis (Cont.)
8

9. STRESSORS AND RISK FACTORS
• Stressors: agents or conditions that can
produce stress and endanger homeostasis
• Physical, chemical, emotional, biological, social, or
cultural
• Vary in scope, intensity, and duration
9

10. STRESSORS AND RISK FACTORS
(CONT.)
• Risk factors: not stressors, but conditions or
situations that increase the likelihood of
encountering a stressor
10

11. NEUROHORMONAL
MEDIATORS OF STRESS AND
ADAPTATION
• Catecholamines: norepinephrine and
epinephrine
• Play an integral role in allostasis
• Sympathico-adrenal system response mediates the
flight-or-fight response
• Adrenocortical steroids: cortisol and
aldosterone
• Critical to maintenance of homeostasis
• May synergize or antagonize effects of
catecholamines
11

12. ENDORPHINS AND
ENKEPHALINS AND IMMUNE
CYTOKINES
• Endorphins and enkephalins: endogenous
opioids (body’s natural pain relievers)
• Raise pain threshold; produce sedation and
euphoria
• Immune cytokines (e.g., interleukin-1):
secreted by macrophages during stress
response, thus enhancing immune system
response
12

13. SEX HORMONES: ESTROGEN,
TESTOSTERONE, AND
DEHYDROEPIANDROSTERONE
• Affect stress responses, thus influencing
allostasis
13

14. GROWTH HORMONE,
PROLACTIN, AND OXYTOCIN
• Growth hormone: can increase during stress
to enhance immune function
• Prolactin: similar to structure of growth
hormone; role in immune response
• Oxytocin: produced during childbirth and
lactation; associated with bonding and social
attachment; thought to moderate stress
response
14

15. ADAPTATION, COPING, AND
ILLNESS
• Individual stress responses: change with time
and circumstances
• Effects of stress response: influenced by
genetics, culture, prior susceptibilities,
preexisting health status, allostatic state, and
ability to manage stress
15

16. ADAPTATION, COPING, AND
ILLNESS (CONT.)
• Adaptation: biopsychosocial process of
change in response to new or altered
circumstances, internal or external in origin
• Coping: behavioral adaptive response to a
stressor using culturally based coping
mechanisms
• Adaptation and coping: terms often used
interchangeably
16

17. ADAPTATION, COPING, AND
ILLNESS (CONT.)
• Distress: perceived inability to cope with a
stressor
• Allostatic overload: inadequate adaptation
mechanisms or overwhelming allostatic load;
results in inability to maintain homeostasis
• Pathophysiologic states result affects all areas of the
body and emotional systems
17

18. ADAPTATION, COPING, AND
ILLNESS (CONT.)
18