Biology 12
The Adrenal Gland
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located above each kidney
made up of 2 glands encased in one “shell”.
o 1. Adrenal medulla – inner gland regulated by Nervous System.
o 2. Adrenal cortex – surrounds the medulla and is regulated by hormones.
Adrenal Medulla
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produces two hormones: epinephrine and norepinephrine
In times of stress, the brain sends a message via the autonomic nervous system to
the adrenal gland. Epinephrine and norepinephrine are released from the adrenal
medulla into the blood.
As a result, blood sugar levels rise as glycogen in the muscles, is converted to
glucose in the blood.
When released into blood, both hormones cause a rise in blood sugar levels as
glycogen in converted into glucose as an energy source. Also increased heart rate,
breathing rate, metabolism. Pupils in eyes dilate to allow more light and clarity of
vision.
Adrenal Cortex
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Produces three types of hormones: glucocorticoids, mineralocorticoids and
sex hormones.
1) glucocorticoids – associated with blood sugar levels.
example: cortisol – increases the level of amino acids in the blood to aid in
recovery from stress. The amino acids are converted into glucose by the liver,
raising blood sugar levels (energy source for cells). Any amino acids not
converted into glucose are available for making new proteins to repair
damaged cells. Fats are also broken down to provide another energy source.
2) mineralocorticoids – associated with body chemistry
example – aldosterone – increases both the storage of sodium in the body and
the amount of water that is reabsorbed by the kidneys. This helps to maintain
the levels of fluids in the body.
Stress Response
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The brain identifies a stressful situation. The hypothalamus secretes a releasing
factor that acts on the anterior lobe of the pituitary causing it to release ACTH. In
a long term stress response, this hormone travels in the blood, targeting the cells
of the adrenal cortex and causing them to release cortisol. Cortisol is carried to
and targets the cells of the muscles and liver. As cortisol levels rise, cells of the
hypothalamus and pituitary decrease the production of their hormones and cortisol
levels fall.
Short term stress responses are regulated by the adrenal medulla by the release of
epinephrine and norepinephrine.
Hormones of the stress response
Hormone
Location of
hormone
production
insulin
beta cells in
isletsof
Langerhans
(pancreas)
glucagon
epinephrine and
norepinephrine
alpha cells in
isletsof
Langerhans
(pancreas)
adrenal medulla
Effect
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cortisol
adrenal cortex
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Increases permeability of cells to glucose;
increases glucose uptake
Allows for the conversion of glucose to
glycogen
Brings about a decrease in blood sugar
Promotes the conversion of glycogen to
glucose
Brings about an increase in blood sugar
Promotes the conversion of glycogen to
glucose
Brings about an increase in blood sugar
Brings about an increase in heart rate, and
cell metabolism
Promotes the conversion of amino acids to
glucose
Promotes the breakdown of fats to fatty acids
Decreases glucose uptake by the muscles
(not brain)
Brings about an increase in blood sugar in
response to stress
Why is insulin inhibition necessary for a stress response?
 Release of stress hormones (epinephrine, cortisol, glucagon) increases blood
glucose to cope with the sustained stress.
 Release of insulin under high blood glucose levels would result in conversion to
glycogen and decrease in blood glucose threatening energy supplies and making it
impossible to sustain a stress response.
 Insulin secretion must be suppressed during these times.
How are blood pressure and blood volume regulated during stress?
 During stress situations, blood flow to the muscles and critical organs (brain,
heart, lungs) is increased but flow to non-essential organs decreases.
 The NS stimulates the kidneys to absorb sodium (Na+), maintaining increased
fluid volume (not explained in the chapter, this would happen as the increased
Na+ in the blood creates a hypotonic environment where the concentration of
solutes in the blood is greatest.
 Hypothalamus activates the posterior pituitary to release ADH. Water will be
reabsorbed in the kidneys (nephrons are the functional units of the kidneys) and
moving into the blood to increase fluid volume.
 Increased fluid volume helps maintain adequate blood pressure during times of
stress.