10/10/20151 the gland and the stress response the adrenal gland and the stress response
TRANSCRIPT
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Aims To explore the role of the adrenal
glands in dealing with stress situations.
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Objectives Label a cross sectional diagram of the gross anatomy of the
adrenal gland
State the two catecholamine hormones secreted by the adrenal
medulla
Describe the key physiological responses stimulated in the adrenal
medulla in the ‘fight or flight’ response
Describe generalized physiological responses in fight and flight
State the major glucocorticoid hormone
State the 3 major actions of glucocorticoid hormones
State the 2 classifications of the gonadocorticoids (sex hormones)
State the major mineralocorticoid hormone
Describe 2 major actions of the mineralocorticoid hormones
(The term ‘corticoid’ indicates ‘produced in the cortex’)(The term ‘corticoid’ indicates ‘produced in the cortex’)
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Endocrine glands
The endocrine glands secrete hormones (chemical
regulators) into the circulation
These glands are also referred to as ductless glands,
and are very vascular
Once in the circulation these hormones then travel to
the target cells
Target cells respond to the hormone by an alteration in
their metabolism
These cells have specific receptor sites to which the
hormone will attach
[Exocrine glands (e.g. salivary ) secrete substances into
a duct.]
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The Adrenal Glands
The adrenal glands produce many different
hormones relating to:
– blood sugar
– mineral transport and fluid balance
– combating stress
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Anatomy of the adrenal glands
Adrenal glands lie in pairs above each kidney (they are "supra-renal“)
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Anatomy of the adrenal glands
Medulla
Zona Glomerulosa
Zona Fasciculata
Zona Reticularis
Capsule (connective tissue)
Zona Glomerulosa, Zona Fasciculata and Zona Reticularis are all part of the adrenal cortex
The adrenal medulla (10% of gland) is completely surrounded by the adrenal cortex (90% of gland) but the two parts differ both in structure and function
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Anatomy of the adrenal glands
Medulla
Zona Glomerulosa secretes ALDOSTERONE
Zona Fasciculata secretes CORTISOL and ANDROGENS
Zona Reticularis secretes CORTISOL
and ANDROGENS
Capsule (connective tissue)
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ADRENAL CORTEX: Zona Glomerulosa
‘Grape-like’ clusters of cells that lie just under the capsule
Releases mineralocorticoids (steroid hormones of the adrenal cortex that regulate electrolyte imbalance)
Main mineralocorticoid = Aldosterone
Aldosterone release is regulated by the renin-angiotensin-aldosterone system (see later in sessions on BP, formation of urine, fluid and electrolytes)
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ADRENAL CORTEX: Zona Glomerulosa
Aldosterone stimulates distal tubules of kidney to pump sodium across basal membrane and thereby attract water
In this way aldosterone helps us to conserve both sodium and water
This raises extracellular fluid volume and hence blood pressure (see later in session on BP)
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ADRENAL CORTEX: Zona Fasciculata
The cells are arranged in cords (long rows) separated
by capillaries
Cells secrete GLUCOCORTICOIDS
Glucocorticoids are steroid hormones secreted by the
adrenal cortex [corticosteroids] that affect the
metabolism of glucose, protein and fat
Release of glucocorticoids is under the influence of
adrenocorticotropin [ACTH]
ACTH is a hormone from the anterior pituitary gland
that stimulates the adrenal cortex in response to
illness, injury, stress and ‘fight’ or ‘flight’ responses
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ADRENAL CORTEX: Zona Fasciculata
The main glucocorticoid in humans is CORTISOL which
is responsible for 95% of all glucocorticoid functions
Cortisol raises blood glucose levels, thereby providing
a source of energy for our responses to stress (in the
flight or fight reaction)
Cortisol is also anti-inflammatory (‘Hydrocortisone’)
(Cortex also produce corticosterone and cortisone –
about 5% of its production)
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Main actions of CORTISOL
1. Gluconeogenesis (‘creation
of new glucose’)
2. Providing resistance to
stress
3. Anti-inflammatory
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CORTISOL: GluconeogenesisGluconeogenesis is the creation of new glucose from non-
carbohydrate sources
i.e. the conversion of proteins and fat to glucose
Glucocorticoids also promote the storage of glucose as glycogen and inhibit glucose inhibit glucose utilization utilization (particularly (particularly in peripheral tissues)in peripheral tissues)
Both of these actions are essential for the maintenance of plasma glucose levels especially during period of prolonged fasting and dieting
Glucocorticoids promote promote lipolysislipolysis (breakdown of fat) and (breakdown of fat) and the consequent release of free fatty acids into the the consequent release of free fatty acids into the blood for blood for energyenergy production production
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CORTISOL: Providing resistance to stress
When exposed to stress (e.g. trauma, hypoglycaemia, perceived life threatening conditions )
anterior pituitary gland releases adrenocorticotrophic hormone (ACTH) adrenal cortex is stimulated to secrete glucocorticoids
increase in available glucose making the body and brain more alert and
provides the raw fuel for energy production.
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CORTISOL: Providing resistance to stress
CLINICAL POINT: If we are under constant stress we are
continually breaking down fat for glucose. If we run away from the stressor we will use
this fat up but if we do not the fat remains in the blood stream and can damage blood vessels, narrowing them as fat deposits lodge under the lining of the vessel walls.
This can in turn lead to the formation of clots, and this, coupled with an already increased blood coagulation can lead to potential for cerebrovascular accident (CVA – ‘stroke’) or heart disease
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CORTISOL: Anti-inflammatory actions
Glucocorticoid hormones inhibit the body’s inflammatory responses to infection, tissue damage, and invasion by foreign particles and proteins (‘anti’ inflammatory)
In this respect they serve to protect the body from excessive inflammatory responses and the potential for causing tissue damage
However this inhibitory effect does not occur when normal levels of glucocorticoids are secreted during everyday day situations and dealing with ‘positive stressors’ – if it did then the inflammatory response would never occur
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ADRENAL CORTEX: Zona Reticularis
This is the zone right next to the This is the zone right next to the medulla and and is seen as a branching network of smaller, dark is seen as a branching network of smaller, dark cellscells
These cells produce a group of hormones known These cells produce a group of hormones known
as as gonadocorticoids
They are regulated also by They are regulated also by ACTH
PrecursorPrecursor androgens androgens are turned into are turned into testosteronetestosterone in testes and in testes and oestrogenoestrogen in ovaries in ovaries
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The adrenal cortex produces steroids that regulate Na+ and K+ balance (mineralocorticoids), steriods that regulate glucose balance (glucocorticoids) and small amounts of steroid sex hormones (DHEA = Dehydroepiandrosterone)
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Adrenal Medulla
The adrenal medulla - inner part of the adrenal
gland
The medulla comprises 10-20% of the whole gland
Derived from embryonic postganglionic
sympathetic neurons / Part of the autonomic
nervous system
The cells of the adrenal medulla are neurons that
have lost their axonal processes and become
neuroendocrine cells
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The Adrenal Medulla The Adrenal Medulla secretes catecholamine
hormones: adrenaline (epinephrine) and nor-adrenaline (nor-epinephrine)
The effects of catecholamines are similar to those produced by activation of the sympathetic nervous system
The major function of the adrenal medulla (in combination with the sympathetic division of the autonomic nervous system) is to prepare the body to resist stress and to respond to emergency situations (the ‘fight’ or ‘flight’ response)
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Disorders associated with the adrenal medulla
An individual can live without the Adrenal Medulla but definitely not without the Adrenal Cortex
If it does need to be removed then individuals need corticosteroid supplements
If an individual develops a tumour of the adrenal gland the hormones produced may alter (e.g. women having two much testosterone developing masculine features, Cushing's Syndrome, Addison's Disease p.306 in Fox 2002)
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Defining Stress! Stress!
[many definitions]
“any physical or psychological threat to the
body, or to the maintenance of homeostasis” or
“any stimulus that creates an imbalance in the
internal environment, or imbalance in
homeostasis which may result in a change in
health status”
(Homeostasis: “ a condition in which the body’s
internal environment remains within certain
physiological limits”)
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Positive Stress
Not all instances where we feel under pressure or stressed have a negative effect upon the body
Some stress is can be therapeutic e.g. the stress involved in positive achievements e.g. at work, or in an exam, or when doing exercise, or in a social situation when meeting new people
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Stressors The stimuli that produce imbalances in
homeostasis are termed stressors These may be physical, psychological or social
in origin and may include: Mental and physical effort Extremes of temperature Fatigue Hypoglycaemia Changes in oxygen / carbon dioxide levels Infections Hypovolaemia Sudden or gradual environmental change Worrying and anxiety Perceived life threatening situations
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The Internal Environment and Homeostasis
Homeostasis of the internal environment will demand that physiological limits / ranges are maintained
Some examples: Glucose: 4-7mmol/L Blood pH: 7.35-7.45 Core body temperature: 36-37.50C Partial pressure of oxygen: 95-105 mmHg Sodium levels: 135-145mmol/L
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Control Systems and Homeostasis
The body responds to any imbalances in homeostasis via two complementary control systems:
– The Nervous System (quick acting)
– The Endocrine System (slow acting)
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Control Systems and Homeostasis
The Nervous System- quick acting via nerve impulses- stimulate cells / organs directly - respond to imbalance is rapid, short lived and may produce an immediate return to homeostasis
However if this does not occur then the ‘back up’ is:
The Endocrine System - slow acting via release of hormones from endocrine glands into the blood - these hormones are transported to distant cells and organs- they then produce an effect to rectify the imbalance
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Physiological responses to stress include Physiological responses to stress include
the integration of the following:the integration of the following:
The Reticular Formation
The Thalamus
The Cerebral Cortex
The Hypothalamus
The Limbic System
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Physiological responses to stressPhysiological responses to stress
The Reticular Formation - modulates mental alertness and skeletal muscle tone
The Thalamus - acts as a relay centre for sensory information
The Cerebral Cortex - facilitates increased vigilance, cognition and focussed attention
The Hypothalamus - modulates the function of both the endocrine and the autonomic nervous systems
The Limbic System - involved with emotions of fear, excitement, rage and anger
Physiological responses to stressPhysiological responses to stress
Musculoskeletal responses
Increased muscle tension
stiffness of the neck, backache and headaches
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ANS and Adrenal Medulla responsesRapid initiation of the ‘fight’ or ‘flight’ response
Adrenal Cortex responseRelease of cortisol maintenance of blood glucose alteration of the immune response
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Three stage model of physiological response to stress (Selye 1975 cited in Porth.C.(2002) Pathophysiology. Concepts of Altered Health States (Sixth edition). Lippincott : Philadelphia.
READ THE SECTION
Stage 1: The alarm reaction
Stage 2: The adaptation, resistance or counter-shock reaction
Stage 3: The stage of exhaustion
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Stages of stress
Alarm reaction- basically equates to the ‘fight’ or ‘flight’ response - cortisol is also released and no one organ is
predominantly activeAdaptation, resistance or counter-shock reaction.- body attempts to return to a steady homeostatic
state or adapt to the new situation via the continued actions of adrenal and other hormones
Stage of exhaustion. - if the body’s attempts to overcome the effects of
the stressor(s) fail and if the adaptation does not occur this will lead to problems such as gastric ulceration, reduced oxygen supply to cells and ultimately death
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Fight or Flight Response
When exposed to a stressful event (e.g. hypovolaemia, perceived life threatening event)
impulses initiated in the hypothalamus and brain stem are transmitted via sympathetic neurons to the adrenal medulla
Adrenaline is released into the blood and carried to target cells / organs which are stimulated to resist stress via the FIGHT or FLIGHT response
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Fight / Flight responses
Iris (eye muscle) Pupil dilation allows more light to enter eye
Salivary Glands Saliva production reduced
Oral/Nasal Mucosa Mucus production reduced
Heart Heart rate and force of contraction increased
LungBronchial muscle relaxed. Increased breathing
Stomach Peristalsis reduced
Small Intestine Motility reduced
Large Intestine Motility reduced
LiverIncreased conversion of glycogen to glucose providing more energy for muscle contraction
Kidney Decreased urine secretion
SkinConstriction of skin arterioles, pallor, hair stands on end / ‘gooseflesh’.
BladderWall relaxedSphincter closed
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The release of adrenaline and nor-adrenaline from the adrenal medulla and their subsequent actions