Lecture 28 - The Stress Response

• Adrenal gland


  Each of the two adrenal glands sits on top of a kidney
• Adrenal cortex


  The outer layer of the adrenal gland. Secretes cortisol and aldosterone.
• Cortisol


  A lipid-soluble hormone secreted by the adrenal cortex in a daily pattern to increase blood fuel, blood pressure, and immunity as well as suppress inflammation. It is the dominant hormone during the resistance phase of the stress response.
• Adrenal medulla


  The inner portion of the adrenal gland. Secretes catecholamines.
• Catecholamines


  Water-soluble hormones (e.g. adrenaline (epinephrine) and noradrenaline (norepinephrine)) secreted by the adrenal medulla during the stress response. Adrenaline is the dominant hormone during the alarm phase of the stress response.
• Stages of the stress response


  • Alarm
  • Resistance
  • Exhaustion
• Sympathetic nervous system


  The nerves activated to help the body respond to stress. Also called the 'fight or flight' system. Activated during the 'Alarm' phase.
• Aldosterone


  A lipid-soluble hormone secreted by the adrenal cortex to stimulate the kidney to reabsorb more Na+ to increase blood volume and pressure.
• Blood pressure must be high enough to ensure blood can be pumped into any organ that needs it.
• Corticotropin-Releasing Hormone (CRH)


  Released by the hypothalamus in response to stress; stimulates the pituitary gland to release ACTH
• Adrenocorticotropic Hormone (ACTH)


  Released by the pituitary gland in response to CRH; stimulates the adrenal glands to produce cortisol
• Aldosterone


  Hormone secreted by the adrenal glands; regulates salt and water balance in the body
• Catecholamines


  Hormones released by the adrenal glands, including adrenaline (epinephrine) and noradrenaline (norepinephrine); involved in the immediate stress response
• Sympathetic Nervous System


  Part of the autonomic nervous system involved in the fight or flight response; activates during stress to increase heart rate, dilate airways, and mobilize energy
• Glucagon


  Hormone released by the pancreas in response to low blood sugar levels; stimulates the liver to release glucose into the bloodstream
• Glycogenolysis


  Process where glycogen stored in the liver and muscles is broken down into glucose for energy
• Lipolysis


  Process where stored fat (lipids) is broken down into fatty acids and glycerol for energy
• Vasoconstriction


  Constriction of blood vessels, leading to increased blood pressure; stimulated by hormones like cortisol and adrenaline during stress
• Oxytocin


  Hormone released during socialization; promotes bonding and reduces stress
• Mindfulness


  Practice of being present in the moment; reduces stress and improves well-being through focused attention and relaxation techniques
• Negative Feedback Loop


  Mechanism where rising cortisol levels inhibit the release of CRH and ACTH, maintaining cortisol balance in the body
• Vasoconstriction


  Constriction of blood vessels, increasing blood pressure; stimulated by cortisol and catecholamines during stress
• Alarm Phase


  Initial response to stress, characterized by increased heart rate, breathing rate, and glucose release, mediated by the sympathetic nervous system and catecholamines
• Resistance Phase


  Prolonged response to stress, characterized by sustained cortisol release, mobilization of energy reserves, and increased blood pressure
• Exhaustion Phase


  Final phase of stress response, where prolonged stress leads to depleted energy reserves and increased risk of health issues
• Socialization


  Activity that stimulates the release of oxytocin, promoting resilience and reducing stress
• Non-stress stimuli for cortisol 


  The stimuli for non-stress cortisol release are day and night rhythm, and/or low blood glucose. 
• In a non-stress environment cortisol causes the pancreas to...

  Release glucagon
• In a non-stress environment, cortisol causes the liver to...


  Reduce glucose intake from blood, and create new glucose (gluconeogenesis)
• In a non-stress environment, cortisol causes skeletal muscle to...


  Reduce glucose intake from blood, and increase protein breakdown (Products are amino acids)
• In a non-stress environment glucose causes fat to....


  Reduce glucose intake from blood, and increase fat breakdown
• Hypothalamic neurons are the control centre for both the sympathetic (fight or flight) and parasympathetic (rest & digest) nervous systems.
• Sympathetic nerves stimulate organs to respond to stress by

  • Pupil dilation
  • Reduced saliva
  • Airway dilation, increased breathing
  • Elevated heart rate, blood pressure
  • Increased glucagon, liver glucose release
  • Decreased digestion, urine production
• Catecholamine Characteristics...

  • Water-soluble
  • Unbound in blood
  • Binds to membrane receptors
  • Initiates second messenger system
  • Amplifies cellular stress responses
  • Response time: seconds to minutes
• Think of the hypothalamus when something is described as releasing or inhibitory!
• Glucagon


  • Produced by the pancreas
  • Raises blood sugar levels by stimulating the breakdown of glycogen in the liver into glucose (glycogenolysis) and promoting gluconeogenesis (production of glucose from non-carbohydrate sources)
• Low blood glucose levels (hypoglycemia) or stress


  Glucagon is released to increase blood sugar levels
• Regulation of glucagon


  Release stimulated by low blood glucose levels and inhibited by high blood glucose levels
• Glucose


  • Obtained from the breakdown of carbohydrates in the diet or from glycogen stores in the liver and muscles
  • Primary source of energy for cells, used in cellular respiration to produce ATP
  • Monosaccharide (simple sugar)
• Regulation of glucose


  Blood glucose levels are regulated by hormones such as insulin (lowers blood sugar levels) and glucagon (raises blood sugar levels)