NURSING 2LA2 Lecture Notes - Lecture 1: Zona Glomerulosa, Zona Reticularis, Locus Coeruleus

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25 Aug 2016
Department
Module 1: Stress and Adaptation
The Stress Response
What is Stress?
There are 3 separate components to stress – the stressors, the stress response and the
pathophysiological sequelae that occurs.
Stressors can be positive (Eustressors) or negative (Distressors) or neutral – these are stressors that
have a neutral effect and they don’t necessarily lead to the stress response until we change them into
negative or positive stressors.
Stressors can come from a variety of sources including the external environment or personal
perception
This non-specific response, whether it is short term or chronic, causes similar hormonal responses
External Stimuli
External stimuli are external demands that trigger emotional, behavioural, and physical reactions.
These stressors can be categorized by three different factors.
First factor is quantity which identifies the negative consequences of stress resulting from an
accumulation of stressors either positive or negative in too short a period of time.
The next factor is quality and there are three major types for this. You have a major change which
affects a large number of people (ex. war). You can have a major change just affecting on or a few
people (ex. divorce) or you can have the daily hassles.
Duration is the last factor. Duration can be acute or time limited. It may be sequential such as the
many changes that follow divorce o it may be chronic intermittent (ex. periodic arguments)
A person can have multiple amounts of stressors with multiple types and they can have varying
durations
Individual Judgement
The stress is basically a demand resource imbalance and people are not passive victims of stressful
forces – but are thinking, feeling, monitoring individuals who are capable of change.
Physiological Response
There are three key areas when we look at this response.
First is the individual’s perception or emotion. Perception such as frustration or anger can lead to the
hormonal release.
The primary hormones involved are glucocorticoids (mainly cortisol), mineralocorticoids (aldosterone),
and the catecholamines (epinephrine, norepinephrine, and a small amount of dopamine)
The last part of the response that we will look at is the potential consequences.
Examples of Stressors
Examples include trauma, surgery, temperature extremes, weather extremes and disasters.
Medications such as chemotherapy, radiation, any malnutrition or prolonged exercise. Pain is a huge
stressor.
Remember the Adrenal Glands
We need to review the adrenal glands before looking at the body’s response to stress
These retroperitoneal glands are comprised of 3 main layers: 1) The outer layer is the capsule which is
fibrous and enclosed in fat for protection. 2) The adrenal cortex forms the majority of the gland and
accounts for 80-90% of the gland. This layer has 3 zones. 3) The inner most layer is the adrenal medulla
which is part of the sympathetic nervous system accounting for 10-20% of the gland.
The adrenal cortex has 3 layers.
Zona Glomerulosa - The outermost layer is the zona glomerulosa which produces mainly aldosterone.
Aldosterone is key for regulating sodium and potassium secretion and retention and it is also a main
component of the renin angiotensin aldosterone pathway for blood pressure control. It also plays a
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role with the pH balance since it facilitates the excretion of hydrogen ions. If someone has too much
aldosterone excreted called aldosteronism, it is usually related to the neoplasms. The person will
present clinically with hypertension and edema due to the high sodium. If too little aldosterone is
secreted, it can lead to hypotension.
Zona Fasciculata - The middle layer is the zona fasciculate – primarily cortisol (95% of gluco corticoid).
Cortisol is released with ACTH stimulation and there is negative feedback with increased cortisol levels.
Cortisol is secreted during periods of stress.
Cortisol promotes lipolysis in the extremities and there seems to be an important acute and long term
effects on the fatty acid metabolism. In the acute stage cortisol promotes the breakdown of fatty acids
to be used as a source for energy. In the long term with sustained cortisol levels, the body starts to
redistribute fat or promote lipogenesis in the face and trunk area. These findings are commonly
referred to as Cushingoid signs.
Cortisol provides an anti-inflammatory effect. This happens at a cellular level but may be linked to
increased autoimmune responses.
It also has a key immune suppressive role causing the T helper 2 shift. Cortisol acts to suppress the
activity of T helper 1 cells leading to a decrease in the cellular immunity and promotes the activity of T
helper 2 cells leading to an increase in humoral immunity and increases the anti-inflammatory
response. This is referred to as the T helper 2 shift.
Cortisol increases blood glucose both by decreasing peripheral uptake and promoting gluconeogenesis.
It decreases insulin sensitivity.
If too little cortisol is secreted, this is called adrenal insufficiency or Addison’s disease. The availability
of cortisol is decreased, limiting the required hormonal effects. If too much cortisol is secreted form
the adrenal cortex, this is called Cushing’s disease.
Key roles of cortisol include hyperglycemia, protein synthesis and catabolism, lipolysis, anti-
inflammatory, and immunosuppression.
Zona Reticularis - The inner most layer of the adrenal cortex is the zona reticularis which is where the
gonadocorticoids are made. They are considered weak androgens. Primarily DHEA and DHEA-Sulphate
are converted to testosterone or estrogen. If too much DHEA is secreted, it can lead to an increase
virilisation or hirsutism, that is facial hair.
Adrenal Medulla - In the middle of the adrenal gland is the adrenal medulla. This is made up of
chromaffins cells also called pheochromocytes. It has a rich blood and nerve supply. Epinephrine is
secreted about 10 times more potent than norepinephrine for the heart and metabolic activities. The
medulla is a minor source of norepinephrine. It has key links to the autonomic nervous system, the
fight or flight component.
A pheochromosytoma is a neuroendocrine tumor which secrete excessive catecholamines.
Physiological Response: HPA axis
When we look at the physiological response we are looking at the hypothalamic-pituitary-adrenal axis
commonly called the HPA axis.
The response is always the same no matter what stimuli or stressor is introduced.
The stressor can be from the external environment or exogenous such as cold or pain or it can be
within us or internal/endogenous such as fear or anxiety.
These stressors activate the limbic system and parts of the cerebral cortex, to ultimately stimulate the
hypothalamus.
The hypothalamus releases corticotropin releasing hormone or factor (CRH or CRF) which in turn
stimulates the sympathetic nervous system by the locus ceruleus, the anterior pituitary and the CRH
stimulates to a lesser extent the posterior pituitary.
When CRH is released, it stimulates the anterior pituitary to release adrenal corticotropic hormone
(ACTH) which is responsible for releasing cortisol from the adrenal gland. Most cortisol is bound to the
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