Stress Response and Adaptation

The Body Strives for Homeostasis

 Homeostasis is the purposeful maintenance of a stable internal environment by coordinated

physiologic processes that oppose change

 Most control systems in the body operate by negative feedback mechanisms, which function

in a manner similar to the thermostat on a heating system

 Can you think of examples?

Hypothalamus

Regulation of Homeostasis

 Body Temperature → triggers sweating to cool you down or shivering to warm you up

 Energy and Hunger → tells you when to eat (hunger) and when you are full (satiety).

 Fluid Balance → controls thirst and signals the kidneys to conserve water via hormones like vasopressin.

 Sleep-Wake Cycles → manages your "internal clock" to regulate when you feel tired or awake.

 Blood Pressure & Heart Rate

 sends signals through the autonomic nervous system to adjust these based on your body's needs

Normothermic State

Stress Response

 System developed in response to any stimuli that makes an intense systemic demand

 Normal, coordinated system meant to increase survival

 Designed to be acute!

What happens when threatened?

ANS stimulation & activation of HPA axis

ANS: Autonomic Nervous System

 Sympathetic

 Parasympathetic

HPA Axis: Hypothalamic-pituitary-adrenal

 neuroendocrine system

 mediates effects of stressors by regulating

metabolism, immune responses, and the

autonomic nervous system (ANS).

Hypothalamic- Pituitary-Adrenal Axis & Role of Cortisol

• too much cortisol: exhaustion/ adaptation syndrome

HPA AXIS responds to stressors by:

• Suppresses osteoblast activity, growth hormone, hematopoiesis

• Suppresses protein & collagen synthesis, suppresses thyroid stimulation hormone

• Antagonizes insulin – glucose increases

• Makes body more responsive to catecholamines

• Inhibits immune response

NEURO, ENDOCRINE, & IMMUNE SYSTEMS ARE TIGHTLY INTERTWINED

• Cytokines can stimulate HPA axis blunting the body's response.

• Protecting cells from an overactive immune response.

• But ... Prolonged hyper-cortisol states increase the risk of infection

General Adaptation Syndrome

• Alarm: fight

• Resistance: wearing out; poor sleep

• Exhaustion

WHAT FACTORS AFFECT THE STRESS RESPONSE?

 Previous responses

 Physiologic reserves

 Psychosocial factors

 Time exposed to stressor

 Age

 Health status

 Gender

 Nutrition

 Sleep wake cycles

 Genetic predisposition

Can affect healthcare