Chapter 5 Notes: Homeostasis, Adaptation and Stress
Homeostasis
Definition: A relatively stable state of physiologic equilibrium.
Function: The body maintains constancy by adjusting and readjusting to changes in the internal and external environments.
Concept emphasis: Stability achieved through dynamic processes, not stasis.
Stressors
Definition: Changes with the potential to disturb equilibrium.
Types:
Physiologic
Psychological
Social
Spiritual
Holism
Two commonly held beliefs:
Both the mind and body directly influence humans.
The mind-body relationship can sustain health or cause illness.
Implication: Entities in physiologic, psychological, social, and spiritual areas contribute to the whole person.
Neurophysiology of Adaptation
Neurotransmitters mediate homeostatic adaptive responses.
Purpose of adaptation: to regulate homeostasis.
Requires use of self-protective properties and mechanisms.
Definition: The response of an organism to change is adaptation.
Neurotransmitters and Neuromodulators
Neurotransmitters (chemical messengers synthesized in neurons):
Serotonin, Dopamine, Acetylcholine, Epinephrine, Norepinephrine, Gamma-aminobutyric acid (GABA), Glutamate
Neuropeptides (neuromodulators):
Substance P, Endorphins, Enkephalins, Other neurohormones
Neuromodulators help neurons communicate; role examples:
Substance P transmits pain sensation.
Endorphins and Enkephalins interrupt Substance P transmission and promote a sense of well‑being.
Central Nervous System
Composition: Brain and spinal cord.
Brain subdivisions:
Cortex: enables abstract thinking, language, memory storage, decision making.
Subcortex (midbrain and brain stem): regulate physiologic activities that promote survival.
The Reticular Activating System (RAS): the mind-body connection link; channels information about internal/external environment through conscious and unconscious processes; generates behavioral and physiological responses via hypothalamic activation.
Modulators affecting RAS activity:
Inhibitory neurotransmitters – GABA
Excitatory neurotransmitters – Norepinephrine
Homeostatic Adaptive Pathways
Autonomic Nervous System
Divisions: Sympathetic nervous system (SNS) and Parasympathetic nervous system (PNS).
Autonomic function: peripheral nerves affecting physiologic functions largely automatic and beyond voluntary control.
Sympathetic Nervous System (SNS)
Function: Prepares body for fight‑or‑flight; accelerates physiologic functions to ensure survival.
Typical effects (illustrative examples):
Pupil: dilation
Saliva: inhibition
Airways: dilation
Heart: increased rate
Liver: glucose release
Digestion/Intestine: inhibition
Adrenal glands: release epinephrine and norepinephrine
Bladder: relaxation
Reproductive system: decreased blood flow
Overall: Heightened alertness and energy mobilization for acute stress.
Parasympathetic Nervous System (PNS)
Function: Restores equilibrium after danger is no longer perceived; inhibits SNS stimulation.
Common label: “Rest and Digest.”
Endocrine System
Description: A group of glands throughout the body that produce hormones.
Role: Sustains the autonomic response and maintains homeostasis by releasing and inhibiting hormones as needed.
System name: Endocrine System
Control of Homeostasis and Feedback (Regulation Diagram)
Feedback loop components:
Input: Information sent along afferent pathway to receptor (sensor)
Change detected by receptor → Stimulus
Control center processes information and initiates response
Output: Information sent along efferent pathway to effector
Effector acts to restore balance (homeostasis)
Output feeds back to influence magnitude of stimulus
Key terms: Stimulus, Imbalance, Variable, Imbalance magnitude, Response
Stress
Physiologic and behavioral responses to disequilibrium.
Occurs when internal or external changes overwhelm homeostatic adaptation.
Has physical, emotional, and cognitive effects.
Signs and Symptoms of Stress
Physical:
Rapid heart rate, rapid breathing, increased blood pressure
Difficulty falling asleep or excessive sleep, appetite changes, muscle tension
Hyperactivity or inactivity, dry mouth, bowel pattern changes, reduced sexual desire
Cognitive:
Impaired attention and concentration, forgetfulness, preoccupation, poor judgment
Emotional:
Irritability, angry outbursts, hypercriticism, withdrawal, depression
Factors That Affect Response to Stress
Intensity, number, and duration of stressors
Physical health status
Life experiences
Coping strategies
Social support
Personal beliefs, attitudes, and values
Physiologic Stress Response
The body’s physical response to stress follows a syndrome with a two- or three-stage pattern:
Alarm stage: immediate physiologic response
Resistance stage: physiologic changes to restore homeostasis
Exhaustion stage: adaptation/resistive mechanisms fail; may become destructive
General Adaptation Syndrome (GAS): studied by Hans Selye ($2$- or $3$-stage pattern)
Alarm Stage (First Stage)
Immediate response to stressor.
SNS neurons rapidly release norepinephrine; adrenal glands release norepinephrine and epinephrine.
Hypothalamus releases corticotropin-releasing factor (CRF).
Pituitary releases adrenocorticotropic hormone (ACTH).
End result: cortisol release from adrenal cortex.
Note: See Table 5-3 in textbook for details.
Stage of Resistance (Second Stage)
Neuroendocrine hormones compensate for the physiologic changes of the alarm stage.
If stress remains or increases, risk for
stress‑related illnesses or disorders rises.
Stage of Exhaustion (Third Stage)
Last phase where adaptive and resistant mechanisms can no longer protect the body.
Beneficial mechanisms become destructive.
Risks: frequent or severe infections, cancer.
As resistance dwindles, physical and mental deterioration occurs, leading to illness and potential death.
Psychological Stress Response
Coping mechanisms: unconscious tactics to defend the psyche (Freud); help prevent feeling inadequate when used appropriately.
When appropriate and moderate, coping mechanisms help maintain mental equilibrium.
Coping strategies: stress‑reduction activities consciously selected to deal with stress-provoking events.
Therapeutic: help gain insight, confidence, emotional maturity.
Nontherapeutic: may provide temporary relief but can lead to maladaptation if overused long-term.
Stress‑Related Disorders
Diseases that result from prolonged stimulation of the autonomic nervous system and endocrine systems.
Many stress‑related diseases involve allergic, inflammatory, or altered immune responses.
Stress can trigger changes in body chemistry:
Autoimmune response
Failure to respond
Weakened immune response
Caring for Stressed Clients (Nursing Implications)
Steps:
Identify the stressors
Assess the client’s response to stress
Eliminate or reduce the stressors
Prevent additional stressors
Promote physiologic adaptive responses
Support the client’s psychological coping strategies
Assist in maintenance of social support
Implement stress reduction/management techniques
Nursing implications: holistic assessment and targeted interventions.
Nursing Implications – Assessment
Use the Social Readjustment Rating Scale to gauge stressors: number and significance of stressors within the previous six months.
Prevention Levels
Primary prevention: reduce risk factors before they occur.
Secondary prevention: early detection and intervention.
Tertiary prevention: minimize complications or deterioration after disease onset.
Stress Reduction Techniques
Goals: promote physiological comfort and emotional well-being.
Practices:
Provide adequate explanations in understandable language
Keep client and family informed
Demonstrate confidence and expertise
Remain calm during crises
Be available to the client; respond promptly to requests
Encourage family interaction
Advocate for the client
Refer to postdischarge resources and support
Stress Management Techniques
Therapeutic activities used to reestablish balance between the sympathetic and parasympathetic nervous systems.
Calming techniques for sympathetic stimulation; stimulating tactics for parasympathetic dominance.
Stress Management Techniques (Examples)
Endorphins
Sensory manipulation
Adaptive activities to enhance adaptation
Alternative thinking
Alternative behaviors
Alternative lifestyles