The Stress Response Flashcards
Desciribe the hypothalamic- pituitary-adrenal axis
- Non-stress stimuli: Day-night rhythmn, low blood glucose
- Hypothalamus secretes: Corticotropin-releasing hormone (CRH)
- Which stimulates the anterior pituitary gland to secrete: Adrenocroticotropin hormone (ACTH)
- Which stimulates the adrenal gland (cortex) to secrete: Cortisol (lipid soluble)
Targets and effector of cortisol: Liver, muscle and adipose (fat) (mobilises fuel); Pancreas (opposes insulin, stimulates glucagon); Cardiovascular system (maintains normal blood pressure), Immune system (supresses/reduces inflammation to increase immunity)
This is a negative feedback loop: Cortisol negatively feeds back to reduce release of ACTH and CRH
Describe the daily pattern of cortisol secretion
- Plasma cortisol concentration fluctuates in a 24-hr circadian rhythm
- Cortisol is highest upon waking up from sleep
- If normal sleep patterns are disturbed, it will affect the normal pattern of cortisol release
Describe the Adrenal Gland location and hormones
Location:
- Two adrenal glands
- Each adrenal gland sits on top of a kidney
Hormones:
- Cortisol - secreted from the cortex (outer layer)
- Aldosterone - secretes from the cortex (outer layer)
- Catecholamines - secreted from the medulla (middle of adrenal gland)
Note: catecholamines are adrenaline (epinephrine) and noradrenaline (norepinephrine)
Describe target cell activation by cortisol
- Cortisol is lipid-soluble and produced as required
- Carried in blood bound to a carrier protein
- Detaches from the carrier protein and enters the target cell
- Cortisol binds to a receptor in the cytosol
- Cortisol-receptor complex enters the nucleus and binds to DNA
- Activates specific genes to produce proteins
- Proteins have effects
- Response time: minutes to days
Describe Cortisol effects - Normal (non-stress)
- Cortisol: Increases blood [glucose] by stimulating:
- Pancreas: to release glucagon
- Liver: to reduce glucose intake from blood, and create new glucose (glyconeogeneisis)
- Skeletal muscle: to reduce glucose intake from the blood, and increase protein breakdown
- Adipose (fat): to reduce glucose intake from blood, and increase fat breakdown - Maintains normal blood pressure
- Supresses inflammation which boosts overall immunity
Overview the ‘Alarm Phase’
- When you’ve been frightened
- What did your body do (response): increased breathing rate, increased heart rate, dry mouth
- How is that response helpful for dealing with the stressor: increased oxygen intake
- increased oxygen and glucose circulated to the brain and skeletal muscle
- reduce activation of unnecessary body functions (eg. digestive, saliva)
Alarm Phase: Stress triggers the sympathetic nervous system. Describe how.
- The stress response begins when distress signals (APs) are sent to the hypothalamus from an emotion centre of the brain
- Hypothalamic neurons are the control centre for both the sympathetic (fight or flight) and parasympathetic (rest and digest) nervous systems
- Stress triggers the hypothalamus to activate the sympathetic nervous system
Alarm Phase: What are the effects of the sympathetic nervous system?
Sympathetic nerves stimulate organs to produce effects that help deal with stress
- Pupils dilate (widen)
- Decreased saliva production
- Dilation of airways and increased breathing rate
- Increased heart rate and blood pressure (vasoconstriction of blood vessels)
- Increased stimulation of glucagon from pancreas; release of glucose from liver
- Decreased digestion and urine productions
Describe how sympathetic nerves stimulate catecholamine
Sympathetic nerves stimulate the adrenal gland (medulla)
- to release adrenaline (epinephrine) and noradrenaline (norepinephrine) into the main bloodstream
- to stimulate target cells to help the body deal with stress
Describe target cell activation by catecholamines
- Catecholamines are water soluble
- Travel in blood unbound
- Bind to membrane receptors
- Initiate actions of a second messenger system
- Lead to amplification of cellular responses that help the body deal with stress
- Response time: seconds to minutes
What are the effects of Catecholamine?
Increased intake of O2 and delivery of blood to cells
- Lungs/Airways: Increased rate of breathing airway dilation (wider)
- Heart: Increased rate and strength of contraction
- Blood Vessels: Increased blood pressure (vasoconstriction)
Increased fuel released into the blood for cells to use
- Liver: Increased glycogen breakdown (glycogenolysis) and making new glucose (gluconeogenesis)
- Skeletal muscle: Increase glycogen breakdown (glycogenolysis)
- Adipose (fat): Increased fat breakdown (lipolysis)
Overview the ‘Resistance’ phase
‘Resistance’ is referring to the body working to resist the effects of stress
- Accuse when stress lasts longer than a few hours
- Cortisol is the dominant hormone of the resistance phase
- Other hormones also play important roles (eg. glucagon, adrenaline, growth hormone, ADH, aldosterone and others)
Hypothalamus secretes CRH to stimulate anterior pituitary cells. Anterior pituitary secretes ACTH to stimulate adrenal cortex cells. Adrenal cortex cells secrete cortisol.
What are the key functions and hormones of the ‘Resistance’ phase?
Fuel mobilisation into blood:
- Cortisol (from adrenal cortex)
- Glucagon (from pancreatic alpha cells)
- Adrenaline (from adrenal medulla)
- Growth hormone (from anterior pituitary
Increased blood pressure:
- Cortisol (from adrenal cortex
- ADH (from porsterior pituitary)
- Aldosterone (from adrenal cortex)
Supressed (reduced) inflammation:
- Cortisol (rom adrenal cortex)
Describe fuel mobilisation into blood plasma
- Energy demands are higher than normal - to deal with stress
- Most hormones secreted in the resistance phase (ie. cortisol, glucagon, adrenaline, growth hormone) act to increase fuel in plasma
- Fats (from adipose) and amino acids (from skeletal muscle) are mobilised for non-neural cells to use
- Glucose is mobilised primarily for neural tissue to use
Explain increased blood pressure in the ‘resistance’ phase
Increased blood pressure ensures blood flow can be directed into organs where it is needed most (eg. the brain)
- ADH (from posterior pituitary) stimulates vasoconstriction of blood vessels
- ADH also stimulates the kidney to reabsorb more water into plasma
- Aldosterone (from adrenal cortex) stimulates the kidneys to reabsorb more Na+ into plasma
Vasoconstriction and isosmotic fluid (water and Na+) retention increases plasma volume, both of which increase blood pressure
Not: cortisol influences blood pressure, but the mechanism is unclear
