Download General Adaptation Syndrome

Endocrine System (part 1) &
General Adaptation Syndrome
Keri Muma
Bio 6
What is the Endocrine
System?
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Composed of glands that
secrete hormones
Responsible for continuous
processes such as growth,
cell metabolism, &
reproduction
What do Hormones Do?
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Hormones are chemical substances that
travel through the blood to a target cell
Target cells must have specific receptors to
which the hormone binds
These receptors may be intracellular or
located on the plasma membrane
They trigger a change in cellular activity
Target Cell Activation

Target cell activation depends on three
factors:
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Blood levels of the hormone
Relative number of receptors on the target cell
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Up-regulation – target cells form more receptors in
response to the hormone
Down-regulation – target cells lose receptors in response to
the hormone
The affinity of those receptors for the hormone
Control of Hormone Release

Hormones are synthesized and released in
response to humoral, neural, and hormonal
stimuli
Control of Hormone Release
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Humoral stimuli - secretion of
hormones in response to
changing blood levels of ions
and nutrients
Examples:

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Concentration of calcium ions in the
blood and the release of PTH
Concentration of blood glucose and
the release of insulin
Control of Hormone Release

Neural stimuli – nerve
fibers stimulate
hormone release

Preganglionic
sympathetic fibers
stimulate the adrenal
medulla to secrete
catecholamines
Figure 16.4b
Control of Hormone Release

Hormonal stimuli – release of
hormones in response to
hormones produced by other
endocrine organs

The anterior pituitary gland
secretes hormones that stimulate
other endocrine glands
Pituitary Gland

Pituitary gland – two-lobed endocrine gland
that secretes nine major hormones
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Neurohypophysis – posterior lobe, made up of neural tissue
Adenohypophysis – anterior lobe, made up of glandular
tissue
Hypothalamus-Pituitary-Axis
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The posterior lobe is a down
growth of hypothalamic neural
tissue and has a neural
connection with the hypothalamus
Nuclei of the hypothalamus
synthesize oxytocin and
antidiuretic hormone (ADH)
These hormones are
transported to the posterior
pituitary where they are
stored and released
Antidiuretic Hormone (ADH)
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ADH (or Vasopressin)
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Triggers increased water reabsorption in the kidney
tubules
Release of ADH is stimulated by:
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Increase in osmolarity detected by the hypothalamus
Decrease in blood pressure and volume
Hypothalamus-Pituitary-Axis

The anterior lobe of
the pituitary and the
hypothalamus are
connected by the
hypophyseal portal
system
Hypothalamus-Pituitary-Axis

Regulatory hormones from the
hypothalamus control the release of
hormones from the anterior pituitary
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Releasing hormones stimulate
the release of hormones
Inhibiting hormones shut
off release of hormones
Anterior Pituitary Hormones
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Tropic hormones – regulates the release of
hormones from other endocrine glands
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Thyroid-stimulating hormone (TSH)
Adrenocorticotropic hormone (ACTH)
Follicle-stimulating hormone (FSH)
Luteinizing hormone (LH)
Growth hormone (GH)
Additional non-tropic hormones released by
the anterior pituitary
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Prolactin (PRL)
Melanocyte-stimulating hormone (MSH)
Anterior Pituitary
Hormones
Growth Hormone (GH)
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Targets most cells, especially bone and skeletal
muscle when young
Growth promoting actions – stimulates bone and
soft tissue growth
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Increases protein synthesis, cell growth, and cell division
Metabolic actions:
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Mobilizes fat stores and increases fatty acid levels in the
blood
Increases blood glucose
 Through glycogenolysis – breakdown of glycogen
 Inhibits skeletal muscle uptake of glucose
Growth
Hormone
Anterior Pituitary Gland
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Adrenocorticotropic hormone
(ACTH)
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Targets the adrenal cortex
Stimulates the release of
glucocorticoids
Adrenal Glands
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Adrenal glands – paired, pyramidshaped organs atop the kidneys
Structurally and functionally, they are
two glands in one
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Adrenal medulla – nervous tissue that
acts as part of the sympathetic NS
Adrenal cortex – glandular tissue
derived from embryonic mesoderm
Adrenal Cortex
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Synthesizes and releases steroid hormones
called corticosteroids
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Zona reticularis – gonadocorticoids
(chiefly androgens)
Zona fasciculata – glucocorticoids
(chiefly cortisol)
Zona glomerulosa – mineralocorticoids
(chiefly aldosterone)
Adrenal Cortex
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Glucocorticoids (Cortisol) - helps the body
resist stress by:
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Increasing blood glucose levels
Cortisol has the following effects :
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Promotes gluconeogenesis - formation of
glucose from non-carbohydrates
Enhances lipolysis
Triggers protein catabolism in skeletal muscle
Suppresses the immune system
Cortisol
Adrenal Cortex
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Mineralocorticoids – regulate the electrolyte
concentrations of extracellular fluids
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Aldosterone – regulates blood pressure, blood
volume, and Na+ and K+ levels in the blood
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Stimulates reabsorption of Na+ by the kidneys
Causes secretion of K+
Mineralocorticoids
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Aldosterone secretion is stimulated by:
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Low blood Na+
Rising blood levels of K+
Decreasing blood volume or pressure
Stress
The Four Mechanisms of
Aldosterone Secretion
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Plasma concentration of sodium and potassium
– directly influences the zona glomerulosa cells
ACTH – causes small increase in aldosterone
during stress
Renin-angiotensin mechanism – kidneys release
renin in response to decreased BP, stimulates
aldosterone release
Atrial natriuretic peptide (ANP) – produced by the
heart in response to increased pressure, inhibits the
release of aldosterone
Renin-Angiotensin-Aldosterone
Pathway

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Is triggered when the kidneys release renin
Renin converts the plasma protein
angiotensinogen into angiotensin I
Angiotensin I is converted into angiotensin II by
ACE (angiotensin converting enzyme)
Angiotensin II:
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Causes systemic arteriole vasoconstriction
Stimulates the adrenal cortex to release aldosterone
Results in increased blood pressure and volume
Mechanisms of Aldosterone
Secretion
Figure 16.13
Got Stress?
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Stress = any factor that disrupts our natural
balance (homeostasis)
Stressor = anything that causes us to adjust
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Can be emotional, physical, environmental
Immediate response to a threat
vs.
Prolonged exposure to stress
How does stress affect you?
General Adaptation Syndrome
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Stress stimulates the hypothalamus to initiate
a chain of reactions that results in general
adaptation syndrome
Definition: “the sum of all non-specific
systemic reactions of the body to long
continued exposure to stress” (Hans Selye)
General Adaptation Syndrome
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Phases of G.A.S.
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Alarm reaction – mobilize resources
Resistance reaction – cope with stress
Exhaustion – deplete reserves
Alarm Reaction
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Immediate response to stress triggers the
sympathetic nervous system “fight or flight”
through the hypothalamus
Mobilizes the body for immediate physical
activity
Short-lived
Stress and the Adrenal Gland
Figure 16.15
Resistance Reaction
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If stress persists longer than a few hours then
the resistance reaction is initiated
Prepares the body for long term protection,
slow to start but longer lasting
The hypothalamus triggers the pituitary gland
to secrete hormones that will allow the body
to continue to survive the stress until
homeostasis is returned
Resistance Reaction
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Overall goal is to:
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Maintain blood pressure and volume
Increase ATP production
Prevent water loss
Prevent inflammation from causing tissue damage
Maintained by ADH, aldosterone, cortisol,
growth hormone, and thyroid hormones
Stress
Posterior
Pituitary
ADH
Anterior Pituitary
Sympathetic
response
Renin –
Angiotensin
ACTH
Adrenal
Cortex
Kidneys
Mineralocorticoids
Aldosterone
Water
retention
Hypothalamus
Retention of Na+
Secretion of K+ / H+
Glucocorticoids
Cortisol
GH
TSH
Thyroid
Liver
T3, T4
Lipolysis
Glycogenolysis
Catabolism of protein & fats
Stimulates glyconeogenesis
Anti-inflammatory &
Immunosuppresent
Cell
metabolism
Excessive Levels of Stress
Hormones
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Prolonged exposure to stress hormones:
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Depresses cartilage and bone formation
Depresses the immune system
Promote changes in cardiovascular, neural,
muscular and gastrointestinal function
(usually due to hypokalemia – potassium deficiency)
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Cardiac arrhythmias
Muscle wasting
Fatigue, concentration loss, irritability
Exhaustion Phase
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If the resistance reaction fails to overcome the
stress eventually the body reserves are exhausted
and the resistance reaction cannot be sustained
The adrenal cortex cannot produce aldosterone and
cortisol
“Link between the breakdown of the hormonal
adaptation mechanism and fatal diseases” Hans
Selye
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Results in illness or death
Cancer, heart disease, depression, hypertension, diabetes
Some Stress is Good!
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We all need a little stress
Norepinephrine which is a neurotransmitter
released during stress plays a role in:
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Creating and retrieving memories
Improves moods (feel good chemical)
How well are you “managing” your stress?