Lecture 6

• Stress can lead to infectious disease, heart disease, reproductive failure, and psychological distress.
• Stress can lead to serious physiological and behavioral changes.
• Kaspar Hauser syndrome occurs in children who stop growing and never go through puberty due to extreme abuse-stress.
• Stallion Stress Experiment by testing cortisol levels while twitching him, running him, or having him mate. All stimulations led to the same raise in cortisol.
• While everyone has experienced stress, it is incredibly difficult to define what stress is.
• The top 2 definitions of stress:

  1. Anything that throws your body out of homeostatic balance.
  2. Stress is the recognition by the body of a stressor, and adaptive responses are the body's attempt to counteract the stressor and reestablish homeostasis.
• Stress response is a suite of physiological and behavioral responses that help to reestablish homeostasis.
• Within seconds, the sympathetic nervous system secretes norepinephrine and the adrenal medulla secretes epinephrine.
• Within minutes, the adrenal cortex begins to secret glucocorticoids and several other hormones are secreted from other endocrine glands.
• Stress response:

  1. Within seconds, the nervous system will response.
  2. Within minutes, the endocrine system will respond.
• The stress response involves two endocrine systems:

  1. Fight-or-flight response
  2. Hypothalamic-Pituitary-Adrenal Axis
• The "fight-or-flight" response includes the secretion of norepinephrine from the sympathetic nervous system and production of epinephrine from the adrenal medulla.
• The HPA axis produces glucocorticoids like cortisol and corticosterone from the adrenal cortex.
• The stress response is generally non-specific and can be generated from many different types of stressors.
• Stress response has evolved from basic survival mechanisms to complex adaptive responses.
• Adaptive responses to the stress response:

  1. Increase in the immediate availability of energy.
  2. Increase in oxygen uptake.
  3. Decrease blood flow to areas not necessary for movement.
  4. Inhibit digestion, growth, immune function, reproduction, and pain perception.
  5. Enhance memory and sensory function.
• Acute stress is the stress response that is activated by stressful stimuli, but deactivated shortly after the stressor subsides.
• Acute stress re-established homeostasis.
• Chronic stress is the stress response activated by stress stimuli but persists either due to a single, persistent stressor or exposure to sequential, multiple stressors.
• Chronic stress results in pathologies.
• HPA Axis

  
• The cortex of the adrenal gland is involved in the secretion of cortisol
• Hormones produced by different parts of the adrenal glands.

  
• Most of the adrenal gland is the cortex (90%) and the rest is the medulla (10%).
• The reticularis is the inner part of the cortex and makes androgens.
• The fasciculata is the middle portion of the cortex and produces cortisol.
• The glomerulosa is the outer part of the adrenal cortex and produces aldosterone.
• The adrenal medulla produces catecholamines.
• The adrenal glands produce glucocorticoids and mineralocorticoids.
• Stress feedback

  
• ACTH release from the adenohypophysis is pulsatile.
• There is a daily cycle of cortisol secretion because it also plays a role in glucose regulation/metabolism.

  
• Cholesteryl ester hydrolase (CEH) frees cholesterol so it is available for conversion to pregnenolone. Pregnenolone is involved in steroidogenesis.
• The HPA Axis:

  1. Hypothalamus - CRH
  2. Pituitary - ACTH
  3. Adrenal Cortex - Cortisol
• The adrenal medulla mainly produces epinephrine.
• The adrenal cortex mainly produces aldosterone, androgens, and cortisol.
• Steroid synthesis, aka steroidogenesis, occurs in the adrenal glands.
• Enzymes determine steroidogenesis.
• Distribution of hormones is due to the differential distribution of steroidogenic enzymes.
• For the adrenal glands, the most important enzymes for steroidogenesis are 17a-hydroxylase and 18-hydroxylase because they are needed for mineralocorticoids and glucocorticoids.