Overview
This lecture explains the physiological responses to stress, focusing on the fight-or-flight and tend-and-befriend responses, as well as the stages of the general adaptation syndrome.
Homeostasis and Stress
- Homeostasis is the body's process of maintaining stable internal conditions like temperature and pH.
- Walter Cannon studied how animals respond homeostatically to stressors (threats or dangers).
- Stressors trigger physiological responses aimed at restoring balance.
Fight-or-Flight Response
- Coined by Walter Cannon to describe the body's reaction to threats: preparing to fight or escape.
- The sympathetic nervous system (SNS), part of the autonomic nervous system, initiates this response.
- SNS increases heart rate and respiratory rate to deliver more oxygen to vital organs.
- Peripheral vasoconstriction directs blood away from limbs toward core organs.
- Nonessential functions like digestion, immune function, and ovulation are suppressed during stress.
Endocrine System and Stress Hormones
- The adrenal glands (on top of the kidneys) release key hormones during stress.
- The adrenal medulla secretes catecholamines (epinephrine/adrenaline and norepinephrine/noradrenaline) to amplify the SNS response.
- The adrenal cortex releases cortisol (a glucocorticoid), which increases blood glucose and suppresses the immune system.
Tend-and-Befriend Response
- Alternative to fight-or-flight, involving social bonding and seeking support.
- Oxytocin, a hormone linked to pair bonding, moderates this affiliative response.
- Estrogen enhances oxytocin effects, making this response more common in women.
General Adaptation Syndrome (GAS)
- Developed by Hans Selye to describe the body's stages of stress response.
- Alarm phase: Immediate reaction to stress with mobilization of resources.
- Resistance phase: Body remains alert and functions at a heightened state.
- Exhaustion phase: Prolonged stress depletes resources, causing tissue damage and increased illness risk.
Key Terms & Definitions
- Homeostasis — the body's maintenance of stable internal conditions.
- Stressors — external threats or dangers triggering stress responses.
- Sympathetic Nervous System — activates the body's rapid involuntary response to dangerous situations.
- Catecholamines — hormones (adrenaline/noradrenaline) from the adrenal medulla that enhance fight-or-flight.
- Cortisol — a glucocorticoid hormone from the adrenal cortex that manages energy and dampens immunity during stress.
- Oxytocin — a hormone promoting social bonding and affiliative behavior.
- General Adaptation Syndrome (GAS) — the three-phase model of stress response: alarm, resistance, exhaustion.
Action Items / Next Steps
- Prepare to discuss the behavioral and emotional impacts of chronic stress in the next lesson.