The Endocrine System
Overview of the Endocrine System
 System of ductless glands that secrete hormones
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Hormones are “messenger molecules”
Secreted into and circulate through the bloodstream
Act on distant target cells with the correct receptors
Specific target cells respond to the hormones
The effects are dependent on the programmed response of
the target cells
Exocrine Glands
For comparison, exocrine glands
secrete substances through a duct
and not into the bloodstream
• Salivary glands: saliva in the
mouth
• Sweat glands
• Mammary glands: milk
• Lacrimal glands: tears
• Sebaceous glands: sebum (waxy
substance)
• The liver and pancreas are both
exocrine and endocrine
Endocrine Organs
 Purely endocrine organs
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Pituitary gland
Pineal gland
Thyroid gland
Parathyroid glands
Adrenal: 2 glands
 Cortex
 Medulla
 Endocrine cells in other organs
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Hypothalamus
Gonads
Pancreas
Thymus
4
HypothalamusPituitary
Complex
Hypothalamus___
Anterior pituitary____
Hypothalamus___________
Pituitary__________
(hypophysis)
_____________Posterior pituitary
Hypothalamus-Pituitary Complex
Pituitary Gland
Anterior lobe
 Hormones are controlled by
releasing hormones and
inhibiting hormones produced
in the hypothalamus
 Tropic hormones control the
release of hormones from
other endocrine glands
Posterior lobe
 Hormones are produced in
the hypothalamus and
secreted through the
posterior lobe
 Divided into 2 lobes
Hypothalamus-Pituitary Complex
Hypothalamus
Via neural connection
Via bloodstream
RH
GH
PRL
MSH
Posterior
Pituitary
Anterior
Pituitary
TSH
ACTH
LH, FSH
Thyroid
Adrenal
Cortex
Gonads
T3, T4
Cortisol
Aldosterone
Testosterone
Estrogen
ADH
Oxytocin
Tropic Hormones
Non-tropic Hormones
Tropic Anterior Pituitary Hormones
Tropic hormones regulate hormone secretion from other glands.
 TSH stimulates the thyroid to
produce and secrete thyroid
hormones
 ACTH stimulates the adrenal
cortex to produce
corticosteroids
 FSH stimulates ovarian
estrogen production in
females
 LH stimulates testosterone
secretion by testes in males
Non-tropic Anterior Pituitary Hormones
Non-tropic hormones stimulate target cells to induce an effect.
 GH (growth hormone) stimulates
growth of bone and muscle, cell
division, and cell regeneration
 PRL (prolactin) stimulates mammary
glands to produce milk
 MSH stimulates melanin (pigment) in
the skin
 FSH stimulates follicle growth in
females; stimulates sperm
production in males
 LH has a role in ovulation and the
growth of the corpus luteum in
females
Negative Feedback Regulating GH
Hypothalamus detects high level and stops secreting GRF
GH level
optimal
level
actual
level
Hypothalamus detects low level and starts secreting GRF
time
Posterior Pituitary Hormones
The posterior pituitary is structurally part of the brain
 ADH (antidiuretic hormone)
stimulates the kidneys to
reclaim more water from
the urine; raises blood
pressure by constricting
blood vessels
 Oxytocin stimulates uterine
contraction during birth and
milk production; involved in
social bonding and sexual
reproduction
Thyroid Gland
• Surrounds the trachea
below the larynx
• Thyroid cells are the
only cells in the body
that absorb and use
iodine
• Thyroid hormones (T3,
T4) regulated by the
anterior pituitary
• Calcitonin regulated
directly by thyroid cells
monitoring blood
calcium levels
Hormones produced by the Thyroid
 Thyroid hormones: T4 and T3
 Regulates metabolism
 Increases basal metabolic rate
 Regulates protein, carbohydrate, and fat
metabolism
 Stimulates vitamin metabolism
 Affects protein synthesis
 Helps regulate bone growth (with GH)
 Stimulates maturing of neurons
 Calcitonin
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Secreted from thyroid cells when blood calcium levels are high
Mechanism for reducing blood calcium levels
Works with PTH from the parathyroid glands
Parathyroid Glands
 Four small glands on the posterior
surface of thyroid gland
 Produces and secretes PTH
(parathyroid hormone)
 PTH functions with calcitonin to
regulate blood calcium levels
 Mechanism for increasing blood
calcium levels
 Works opposite of calcitonin from
the thyroid
 Stimulate Vitamin D to uptake
calcium from the intestines
 Release regulated directly by
parathyroid cells monitoring blood
calcium levels
Regulation of Blood Calcium
Negative Feedback Regulating Blood Calcium
blood calcium level
Thyroid C cells detect high level and secrete calcitonin
optimal
level
actual
level
Parathyroid cells detect low level and secrete PTH
time
Adrenal Glands
 On top of the kidneys
 Each is really two endocrine glands
 Adrenal cortex (outer): secretes corticosteroids (Aldosterone & Cortisol)
 Adrenal medulla (inner): secretes Epinephrine (Adrenaline) and Norepinephrine
 Unrelated chemicals but all help with stress and extreme situations
Aldosterone
 Secreted by adrenal cortex
in response to a decline in
either blood volume or
blood pressure (e.g.
severe hemorrhage)
 Stimulates kidneys to
reabsorb more sodium
(Na)
 Water passively follows
 Blood volume increases
Cortisol
 Helps the body deal with
stressful situations within
minutes
 Physical: trauma, surgery,
exercise
 Psychological: anxiety,
depression, crowding
 Physiological: fasting,
hypoglycemia, fever, infection
 Regulates or supports a variety
of important cardiovascular,
metabolic, immunologic, and
homeostatic functions
including water balance
Cortisol, continued
 Keeps blood glucose levels high enough to support brain’s activity
 Forces other body cells to switch to fats and amino acids as energy sources
 Catabolic: breaks down proteins
 Redirects circulating lymphocytes to where pathogens are
 In large quantities, depresses immune and inflammatory response
Adrenal Medulla
 Part of autonomic nervous
system
 Secretes epinephrine
(adrenaline) and
norepinephrine (both
hormone and
neurotransmitter)
 Fight, flight, fright
 Vesicles store the
hormones
 Instantly released by the
autonomic nervous system
when needed
Gonads (testes & ovaries)
main source of the steroid sex hormones
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Testes
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Secretes Testosterone in response
to stimulation from LH
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Maintains secondary sex
characteristics
Helps promote sperm formation
Ovaries
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Androgens secreted after
stimulation from FSH
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Directly converted to Estrogen by
follicular granulosa cells
Granulosa cells also produce
Progesterone
Corpus luteum also secretes
estrogen and progesterone
Pineal Gland
 Located deep in the center of the brain
 Melatonin
 Regulates the circadian rhythm (biological clock) of the sleep/wake cycle
 Secretion is regulated by light via visual input – low during the daylight
hours, high during the darkness hours
 Called the “third eye” because of its ability at photoreception
 Also has some effect on the release of LH and FSH from the anterior
pituitary gland
Pancreas
Exocrine and Endocrine cells
 Most cells of the pancreas
 Exocrine function: secrete digestive enzymes (pancreatic juice) – alkaline
for neutralization of acidic stomach juices
 Islet cells of Langerhans
 Endocrine function: regulates blood sugar (glucose) level directly
Alpha cells:
secrete Glucagon which raises
blood sugar
Beta cells: secrete Insulin
which lowers blood sugar
Regulation of Blood Glucose
Negative Feedback Regulating Blood Glucose
blood glucose level
β cells detect high level and secrete Insulin
optimal
level
actual
level
α cells detect low level and secrete Glucagon
time