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Endocrine System
Tortora Chapter 18, edition 13
Ebaa M Alzayadneh, DDS, PhD
Integrative Physiology and Pharmacology
• Regulated by
• Signals from nervous
system
• Chemical changes in
the blood
• Other hormones
• Most hormonal
regulation by negative
feedback
• Few examples of
positive feedback
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Endocrine System Overview
3
• Hypothalamus is a major link between
nervous and endocrine system
• Pituitary is attached to hypothalamus by
infundibulum and divided in to:
• Anterior pituitary or adenohypophysis
• Posterior pituitary or
neurohypophysis
• The anterior pituitary receives signalling
molecules from the hypothalamus, and in
response, synthesizes and secretes seven
important hormones.
• The posterior pituitary does not produce
any hormones of its own,but, it stores and
secretes two hormones made in the
hypothalamus.
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Hypothalamus and Pituitary
Gland
4
Hypothalamus
and Pituitary
Gland
• Release of hormones is stimulated by
hypothalamus releasing hormones (factors).
• Regulated by negative feedback
• Hypothalamic hormones made by
neurosecretory cells transported by
hypophyseal portal system to ant. pituitary.
• Anterior pituitary hormones that act on other
endocrine systems called tropic hormones,
synthesizing cells are called trophs cells.
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Anterior pituitary
6
Anterior pituitary
To memorize ant. Pituitary hormones
F: Follicle Stimulating Hormone
L: Luteinizing Hormone
A: ACTH : Adrenocorticotropic hormone
G: Growth Hormone
T: Thyroid Stimulating Hormone
O: MSH - melanOcyte stimulating hormone
P: Prolactin
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"FLAGTOP"
7
• Follicle-stimulating hormone (FSH) by gonadotrophs cells
• Ovaries initiates development of oocytes, testes stimulates
testosterone production
• Luteinizing hormone (LH) by gonadotrophs cells
• Ovaries stimulates ovulation, testes stimulates testosterone
production
• Adrenocorticotropic hormone (ACTH) or corticotropin
• Released by corticotrophs cells
• Stimulates glucocorticoid secretion by adrenal cortex
• Thyroid-stimulating hormone (TSH) or thyrotropin by
thyrotrophs
• Stimulates synthesis and secretion of thyroid hormones by
thyroid
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Hormones of the Anterior Pituitary
(FLAG TOP)
8
• Prolactin (PRL):released by lactotrophs
• Promotes milk secretion by mammary glands
• Melanocyte-stimulating Hormone (MSH)
• Unknown role in humans
• Human growth hormone (hGH) or somatotropin released
by somatotrophs
• Stimulates secretion of insulin-like growth factors
(IGFs) that promote growth, protein synthesis
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Hormones of the Anterior
Pituitary
9
ANTERIOR PITUITARY HORMONES
Hypothalamus
Hormone that
stimulate
Hormone released
from
Adenohypophysis
(ant. Pituitary)
Major Function/ Target
Also called somatotropin,
stimulates secretion of
insulin-like growth factors
(IGFs) that promote growth
Thyrotropin
releasing hormone
(TRH)
Thyroid Stimulating
Hormone (TSH)
Stimulates synthesis and
secretion of thyroid
hormones by the thyroid
gland
Prolactin (PRL)
Stimulates breast growth, 10
and development of the
mammary glands
Prolactin inhibiting
hormone (PIHdopamin)
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Growth hormone
releasing and
Human Growth
inhibiting hormones Hormone (hGH)
(GHRH, GHIH)
ANTERIOR PITUITARY HORMONES
Gonadotropic
releasing
hormone
(GnRH)
Gonadotropic
releasing
hormone
(GnRH)
Hormone
released from
Adenohypophysis
Major Function/ Target
Follicle
Stimulating
hormone (FSH)
Ovaries initiate
development of oocytes;
testes initiate development
of spermatozoa
Luteinizing
hormone (LH)
Ovaries stimulate
ovulation; testes stimulate
testosterone production
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Hypothalamus
Hormone
11
ANTERIOR PITUITARY HORMONES
Corticotropin
releasing hormone
(CRH)
Corticotropin
releasing hormone
(CRH)
Hormone released
from
Adenohypophysis
Major Function/ Target
Adrenocorticotropic
Hormone (ACTH)
Stimulates release of
mineralocorticoid,
glucocorticoid, and androgen
hormones from the adrenal
cortex
Melanocyte
Stimulating hormone
(MSH)
Stimulate the production and
release of melanin by
melanocytes in skin and hair.
12
MSH signals to the brain have
effects on appetite and sexual
arousal
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Hypothalamus
Hormone
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Negative Feedback Regulation
13
Pituitary Hormones
• Anterior Pituitary:
• Trophic effects:
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• High blood
[hormone] causes
target organ to
hypertrophy.
• Low blood
[hormone] causes
target organ to
atrophy.
14
1 Low blood1glucose
Low blood glucose 6 High blood6 glucose
High blood glucose
(hypoglycemia)
(hyperglycemia)
(hypoglycemia)
(hyperglycemia)
stimulates release
of release of
stimulates release
of release of
stimulates
stimulates
GHIH
GHRH
2 GHRH stimulates
2 GHRH stimulates
secretion
secretion
of hGH by of hGH by
somatotrophssomatotrophs
Effects
of hGH
and
IGFs
hGH
GHIH
High levels of GH
before puberty
causes Gigantism,
after puberty causes
Acromegaly.
Low levels of GH
before puberty
causes Dwarfism,
after puberty leads
to some Metabolic
15
effects
7 GHIH inhibits
7 GHIH inhibits
secretion of secretion of
hGH by
hGH by
somatotrophssomatotrophs
hGH
Anterior
pituitary
Anterior
pituitary
3 hGH
8 ofAhGH
and IGFs speed
low and
level of hGH and
3 hGH and IGFs
8 A low level
speed
upofbreakdown
of liver
IGFs
the rate
up breakdown
liver
IGFs decreases
thedecreases
rate
of glycogen breakdown
glycogen intoglycogen
glucose, into glucose,
of glycogen breakdown
enters the blood
in the
liver and glucose
which enterswhich
the blood
in the liver and
glucose
enters
the blood more
more rapidly more rapidly
enters the blood
more
slowly
slowly
4 Blood
9 Blood
level glucose level
level glucose level
4 Blood glucose
9 Blood glucose
rises to normal
falls to normal
rises to normal
falls to normal
(aboutmL)
90 mg/100 mL)
(aboutmL)
90 mg/100 mL)
(about 90 mg/100
(about 90 mg/100
5 If blood glucose10 If blood glucose
5 If blood glucose
continues to continues
increase, to increase,
continues to decrease,
hyperglycemia
inhibits
hyperglycemia inhibits
hypoglycemia inhibits
release of GHRH release of GHIH
release of GHRH
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GHRH