Lecture 21, The Endocrine Stress Response Flashcards
Hormone Metabolism and Excretion
after a hormone has completed its function, it must be removed or cleared from the blood to prevent excessive, prolonged, or harmful effects on the target tissue
a hormone’s concentration in the plasma depends on:
- the rate of secretion from the endocrine gland
- the rate of removal (clearance) from the blood
hormone clearance from the blood can occur by:
- excretion from the body via the urine
- metabolic transformation into an inactive from
◦ can occur in the liver, kidneys, or the hormone’s
target tissue
◦ with some peptide hormones, the binding of the
hormone to the receptor creates a complex that is
endocytosed into the cell, where they can be
catabolized intracellularly, and the receptors
returned to the plasma membrane surface
- degradation of the hormone into subunits that can be recycled and used to synthesize other substances
* the liver and the kidneys are major organs that metabolize or excrete hormones
Types of Endocrine Disorders (at the level of gland)
endocrine disorders can be classified based on dysfunction at the level of the endocrine gland, or dysfunction at the level of the tissue tissue:
at the level of gland:
hypersecretion - when the endocrine gland is producing too much hormone(s)
◦ primary hypersecretion occurs when the gland is
inherently overproducing the hormone(s)
◦ secondary hypersecretion occurs when the cause
is excessive stimulation by a tropic hormone
hyposecretion - when the endocrine gland is not producing enough hormone(s)
◦ primary hyposecretion occurs when the cause is
glandular damage, enzyme deficiency, or iodine
deficiency (in the case of T4 and T3)
◦ secondary hyposecretion occurs when the cause
is inadequate stimulation by its tropic hormone,
or excessive inhibitory stimulation (example:
secondary hypothyroidism)
Type of Endocrine Disorders (at the level of the target tissue)
endocrine disorders can be classified based on dysfunction at the level of the endocrine gland, or dysfunction at the level of the target tissue
at the level of the target tissue:
hyperresponsiveness - when the endocrine is producing enough hormone, but the target tissue becomes hypersensitive to the hormone
◦ can form as a result of excessive expression of
the receptor on the target tissue
hyporesponsiveness - when the endocrine is producing enough hormone, but the target tissue does not respond normally to the hormone (example: type II diabetes mellitus)
◦ can form as a result of a loss of receptors on the
target tissue, or dysfunction in a signalling
pathway within the cell, in inability to convert the
hormone to an active form
Cortisol
cortisol is widely known as the body’s stress hormone (although it does have a variety of other functions)
- stress: a real or perceived threat to homeostasis
◦ physical trauma, emotional stress/trauma,
extreme environmental conditions, pain, sleep
deprivation, infection/illness, and more
◦ distress: stress that negatively affects an
individual
◦ eustress: stress that positively affects an
individual
when under stress, the hypothalamus is stimulated to secrete corticotropic-stimulating release hormone into the hypothalamo-hypophyseal portal vessels
- CRH stimulates ACTH release from the anterior pituitary
- ACTH travels in the blood (water-soluble) to the adrenal cortex
- the adrenal cortex secretes cortisol into the blood, transported by corticosteriod-binding globulins (CBGs) to target tissues
stress can also stimulate vasopressin release from the posterior pituitary, which can evoke ACTH release
stress on the immune system (ex. infection or illness) causes the release of cytokines, which also stimulate CRG or ACTH release
Cortisol - Function
systemically, cortisol has anti-inflammatory and anti-immune functions
- inhibits the production of inflammatory chemicals (like prostaglandins)
- suppresses the growth and function of some immune cells
- prevents excessive immune responses
as a stress hormone, cortisol functions in enabling several fight-or-flight responses
- enable vascular smooth muscle responsiveness to NE and E
◦ allows for vasoconstriction and maintained or
increased blood pressure
- stimulates glucagon secretion, and inhibits insulin secretion
◦ Increases plasma [glucose]
- stimulates the increase in plasma concentrations of glucose, amino acids, glycerol, and fatty acids
during fetal and neonatal development, cortisol contributes to the production of surfactant
surfactant
a fluid found on lung epithelial tissue that decreases lung surface tension; makes it easier for lungs to inflate during inspiration
Stress Response - Other Hormones
cortisol is just one component of a milieu of hormones released in response to stress
- ACTH – stimulates cortisol release from the adrenal cortex
* aldosterone and vasopressin – maintain blood volume and [Na+]
◦ particularly important in cases of physical stress
such as trauma and blood loss, and strenuous
endurance exercise
* growth hormone and glucagon – mobilizes energy stores
* during stress, insulin release is inhibited
sympathetic system activation stimulates epinephrine secretion from the adrenal medulla
* the functions of epinephrine during stress are described in the table below
Hypothalamic Pituitary Adrenal (HPA) Axis
the HPA axis refers to the signalling pathway between the hypothalamus, anterior pituitary, and adrenal cortex during the stress response
- the HPA axis is a neuroendocrine mechanism that influences various organ systems and physiological phenomena, including the immune system, metabolism, and autonomic responses
the presence of a stressor is sensed and relayed to the hypothalamus
- CRH release into hypothalamo-hypophyseal portal vessels
- ACTH release into general circulation
- cortisol release from the adrenal cortex
- cortisol binds to target tissues to elicit an appropriate response to the stressor
General Adaptation Syndrome (GAS)
general adaptation syndrome describes the body’s response to chronic stress over time, which involve three phases:
1. alarm phase: the fight-or-flight response
◦ with short-term stress, the body stops at this
phase, and returns to rest
◦ mediated by epinephrine and norepinephrine
release from the adrenal medulla
2. resistance phase: the body’s attempt to adapt to
the stressor
◦ if the stressor persists, the body attempts to
adapt to the stressor, and recover from the alarm
phase
3. exhaustion phase: dysfunction and homeostatic
dysregulation as a result of chronic stress
◦ if the stressor persists for extended durations,
chronic cortisol release negatively impacts several
tissues and organs, leading to:
‣ depression and mood shifts,
immunosuppression, severe fatigue, and
cardiovascular issues
alarm phase - responses
alarm phase - responses:
* typical fight-or-flight responses (dilated pupils, heightened senses, increased heart rate, increased respiration)
* trembling
* pale or flushed skin
resistance phase - responses
resistance phase - responses:
* gastrointestinal issues
* mood dysregulation (sadness, irritability, frustration)
* headaches
* sleeplessness and poor concentration
exhaustion phase - responses (adrenal fatigue)
- decreased stress tolerance
- burnout and persistent fatigue
- persistent mood dysregulation (depression and anxiety)
- immunosuppression
“adrenal fatigue” refers to the collection of symptoms observed during the exhaustion phase - is not an accepted medical term/condition, but is a theory often used by lay people when describing burnout
