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Endocrine System
The Pituitary Gland
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Known as the “Master Gland”: it is
the “checks and balances” system
via the negative feedback
mechanisms
Located in the cerebrum
Anterior lobe: glandular tissue;
makes hormones
– Tropic hormones: stimulate other
endocrine glands to make their
hormones; thyrotropic,
adrenocorticotropic, and two
gonadotropic hormones
– NonTropic hormones: exert effects
on non-endocrine targets; growth
hormone and prolactin
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Posterior lobe: nervous tissue;
storage area for hormones made by
hypothalamic neurons; oxytocin and
antidiuretic hormone
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Anterior: Stimulates the thyroid gland,
Stimulates adrenal cortex, ACTH, GH
Posterior: Causes contractions of the
uterus, Regulates water balance
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The Pituitary Gland
• The hypothalamus
controls the pituitary
gland
– Anterior: a releasing factor
that is produced in the
hypothalamus and
transmitted to the anterior
lobe commands release of
hormones to their target
cells
– Posterior: storage area for
hormones made by
hypothalamic neurons;
oxytocin and antidiuretic
hormone
Pituitary Hormones
Pituitary Hormones
Pineal Gland
• Located in 3rd ventricle or
epithalamus of the brain
• Secretes melatonin
– inhibits reproductive
system (especially in
females) so adult body size
is reached before sexual
maturation occurs
– Establishes biorhythms
(sleep-wake cycles)
Thyroid Gland
• Located at base of throat
inferior to the Adam’s
apple
• Two lobes joined in the
middle by the isthmus
• Largest endocrine gland
in the body
• Works closely with the
Islets of Langerhans in
glucose metabolism
Thyroid Hormones
• T3 or triiodothyronine:
increases oxygen consumption
and metabolism of all cells;
regulates energy levels
• T4 or thyroxine: regulates
metabolism for the production
of heat and energy in body
tissue by controlling rate at
which glucose is oxidized
• Calcitonin or thyrocalcitonin:
active in calcium metabolism,
lowers calcium levels in the
blood by inhibiting release of
calcium from bone
Parathyroid Glands
• Located on the posterior
aspect of the thyroid
• 2 parathyroids on each
lobe of the thyroid totaling
4 parathyroid glands
• Parathyroid hormone or
parathormone: most
important regulator of
calcium ion homeostasis
in the blood; causes
increase in blood calcium
levels which works in
opposition to calcitonin
Thymus Gland
• Located in the upper
thorax just posterior
to the sternum
• Decreases in size as
person ages
• Thymosin: “incubator”
for maturation of Tlymphocytes; partially
controls immune
system
Adrenal Glands
• Located on the upper end
of the kidney
• Two parts:
– Adrenal Cortex: outer part;
produces steroid hormones
collectively called
corticosteriods
– Adrenal Medulla: inner
part; similar to post.
Pituitary gland, made up of
nervous tissue and
releases hormones when
stimulated by sympathetic
nervous system called
catecholamines
Adrenal Hormones
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Adrenal Cortex Hormones
– Mineralocorticoids:
Aldosterone- regulates
amount of Na and K+ in
the body; which works in
conjunction with ADH
from the Post. Pituitary
to maintain water or
electrolyte balance
– Glucocorticoids: Cortisolregulates metabolism of
proteins, fats, and carbs
– Gonadocorticoid: male
androgen testosterone
and progesterone –
maintains secondary sex
characteristics,
supplements sex
hormones secreted by
glands
Adrenal Hormones
• Adrenal Medulla
Hormones
– Epinephrine/adrenalin
and norepinephrine:
used in the alarm
stage of the “flight or
fight” response,
increases heart rate,
blood pressure, and
blood glucose levels,
dilates small passage
ways of the lungs
resulting in more
oxygen and glucose in
the blood and faster
circulation of the
blood to body organs
Pancreas- Islets of Langerhans
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Located close to stomach in
the abdominal cavity
Both exocrine (has ducts) and
endocrine (into the blood
stream)
Specifically the Islets of
Langerhans are the endocrine
tissue in the pancreas which
produce hormones that are
released directly into the
bloodstream
– Glucagon: increases blood
glucose (hyperglycemic)
– Insulin: decreases blood
glucose, only hormone that is
hypoglycemic, absolutely
necessary is only way that
glucose can get to cells to be
used
– How insulin works
Gonads
• Male = testes(2)
– Testosterone: develops
and maintains male
secondary sex
characteristics
• Female = ovaries(2)
– Estrogen: controls
menstrual cycle, prepares
the uterus for implantation
and pregnancy
– Progesterone: develops
and maintains female
secondary sex
characteristics
Negative Feedback
• Definition: feedback that
regulates the stimulus; a
high concentration of a
hormone in the blood has
an inhibiting effect on its
gland.
• Hormone levels increase
or decrease as the target
organ requires; endocrine
glands work together to
maintain homeostasis.
Hyper- and Hypofunctions of
Hormones
Growth Hormone
• Hyperfunction:
– Gigantism (child)
– Acromegaly (adult)
• Hypofunction:
– Dwarfism (child)
Hyper- and Hypofunctions of
Hormones
Thyroxine
• Hyperfunction
– Goiter: enlarged
thyroid due to iodine
deficiency
– Grave’s Disease:
hyperthyroidism
resulting in eyes
bulging anteriorly
(exophthalmos)
Hyper- and Hypofunctions of
Hormones
• Thyroxine (cont.)
• Hyperfunction
– Cretinism: occurs in
children resulting in stunted
growth
– Myxedema: occurs in
adults resulting in a
decreased metabolism
causing physical and
mental sluggishness,
obesity, chronic edema,
poor muscle tone, and low
body temperature
Hyper- and Hypofunctions of
Hormones
Insulin
• Hyperfunction
– Hypoglycemia: deficiency
of sugar in blood
• Hypofunction
– Diabetes Mellitus: caused
by deficient insulin release,
leading inability of the body
cells to use carbs at a
normal rate. The three
cardinal signs: 1) polyuria,
2) polydipsia, and
3) polyphagia
Hyper- and Hypofunctions of
Hormones
Steroids (adrenal cortex)
• Hypofunction
– Addison’s Disease: caused
by deficient secretion of
adrenal cortical hormones;
characterized by bronze
tone of the skin
• Hyperfunction
– Cushing’s Syndrome:
caused by excess
adrenocortical;
characterized by increased
weight gain and fat
acculumation,
osteoporosis, and a “moon
shaped” face
Miscellaneous Facts about the
Endocrine System
• Endocrine glands are ductless
and secrete hormones directly
into the bloodstream.
• Hormones are organic
substance (chemical, steroid,
or proteins) secreted by cells
into the bloodstream that has
an effect on metabolic activity
of another cell (target organ);
they are chemical messengers
that help regulate cell activity
• Hormones travel to all parts of
the body but only affect their
target cells
• Hormones are excreted by the
kidneys in urine