1. 13.11: Stress and Its Effects
Survival depends on maintaining homeostasis
Factors that change the internal environment are potentially life-threatening
Sensing such dangers directs nerve impulses to the hypothalamus
This can trigger a loss of homeostasis

2. Types of Stress Two types of stress: Physical stress
Psychological stress

3. Responses to Stress Stress results from changes
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Stress results from changes
in the external environment
Hormonal signals
Neural signals
Signals from
sensory receptors
Sympathetic impulses
Hypothalamus
CRH released
Adrenal medulla
Anterior pituitary
Epinephrine and
norepinephrine
released
Norepinephrine
released
ACTH released
Adrenal cortex
Short-term “fight or flight” or alarm stage.
Cortisol released
• Blood glucose increases.
• Blood glycerol and fatty acids increase.
Long-term adjustment or resistance stage
• Heart rate increases.
• Blood pressure rises.
• Increase in blood concentration of amino acids.
• Breathing rate increases.
• Increased release of fatty acids. •
Air passages dilate.
• Increased glucose formed from
noncarbohydrates—amino acids (from
proteins) and glycerol (from fats).
• Pupils dilate.
• Blood flow redistributes.