1. Faisal I. Mohammed, MD, PhD
Endocrine System L3
Faisal I. Mohammed, MD, PhD
University of Jordan

2. Hypothalamus and Pituitary Gland

3. Anterior pituitary
Release of hormones stimulated by releasing and inhibiting hormones from the hypothalamus
Also regulated by negative feedback
Hypothalamic hormones made by neurosecretory cells transported by hypophyseal portal system
Anterior pituitary hormones that act on other endocrine systems called tropic hormones
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4. Hormones of the Anterior Pituitary
Human growth hormone (hGH) or somatotropin
Stimulates secretion of insulin-like growth factors (IGFs) that promote growth, protein synthesis
Thyroid-stimulating hormone (TSH) or thyrotropin
Stimulates synthesis and secretion of thyroid hormones by thyroid
Follicle-stimulating hormone (FSH)
Ovaries initiates development of oocytes, testes stimulates testosterone production
Luteinizing hormone (LH)
Ovaries stimulates ovulation, testes stimulates testosterone production
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5. Hormones of the Anterior Pituitary
Prolactin (PRL)
Promotes milk secretion by mammary glands
Adrenocorticotropic hormone (ACTH) or corticotropin
Stimulates glucocorticoid secretion by adrenal cortex
Melanocyte-stimulating Hormone (MSH)
Unknown role in humans
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6. Negative Feedback Regulation
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7. Hypothalamic Control of the Anterior Pituitary
Hormonal control rather than neural.
Hypothalamus neurons synthesize releasing and inhibiting hormones.
Hormones are transported to axon endings of median eminence.
Hormones secreted into the hypothalamo-hypophyseal portal system regulate the secretions of the anterior pituitary
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8. Feedback Control of the Anterior Pituitary
Anterior pituitary and hypothalamic secretions are controlled by the target organs they regulate.
Secretions are controlled by negative feedback inhibition by target gland hormones.
Negative feedback at 2 levels:
The target gland hormone can act on the hypothalamus and inhibit secretion of releasing hormones.
The target gland hormone can act on the anterior pituitary and inhibit response to the releasing hormone.
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9. Feedback Control of the Anterior Pituitary (continued)
Short feedback loop:
Retrograde transport of blood from anterior pituitary to the hypothalamus.
Hormone released by anterior pituitary inhibits secretion of releasing hormone.
Positive feedback effect:
During the menstrual cycle, estrogen stimulates “LH surge.”
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10. Higher Brain Function and Pituitary Secretion
Axis:
Relationship between anterior pituitary and a particular target gland.
Pituitary-gonad axis.
Hypothalamus receives input from higher brain centers.
Psychological stress affects:
Circadian rhythms.
Menstrual cycle.
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11. Effects of hGH and IGFs
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 effects
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12. Pituitary Hormones Anterior Pituitary: Trophic effects:
High blood [hormone] causes target organ to hypertrophy.
Low blood [hormone] causes target organ to atrophy.
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13. Posterior pituitary Does not synthesize hormones
Stores and releases hormones made by the hypothalamus
Transported along hypothalamohypophyseal tract
Oxytocin (OT)
Antidiuretic hormone (ADH) or vasopressin
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14. Posterior Pituitary Hormones
Stores and releases 2 hormones that are produced in the hypothalamus:
Antidiuretic hormone (ADH/vasopressin):
Promotes the retention of H20 by the kidneys.
Less H20 is excreted in the urine.
Oxytocin:
Stimulates contractions of the uterus during parturition.
Stimulates contractions of the mammary gland alveoli.
Milk-ejection reflex.
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15. Hypothalamohypophyseal tract
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16. Hypothalamic Control of Posterior Pituitary
Hypothalamus neuron cell bodies produce:
ADH: supraoptic nuclei.
Oxytocin: paraventricular nuclei.
Transported along the hypothalamo-hypophyseal tract.
Stored in posterior pituitary.
Release controlled by neuroendocrine reflexes.
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17. Oxytocin (OT)
During and after delivery of baby affects uterus and breasts
Enhances smooth muscle contraction in wall of uterus
Stimulates milk ejection from mammary glands
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18. Antidiuretic Hormone (ADH)
Decreases urine production by causing the kindeys to return more water to the blood
Also decreases water lost through sweating and constriction of arterioles which increases blood pressure (vasopressin)
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19. Osmoreceptors
High blood osmotic
pressure stimulates
hypothalamic
osmoreceptors
Low blood osmotic
pressure inhibits
Nerve impulses
liberate ADH from
axon terminals in
the posterior
pituitary into
the bloodstream
activate the
neurosecretory cells
that synthesize and
release ADH
Hypothalamus
Sudoriferous
(sweat) glands
decrease water
loss by perspiration
from the skin
Arterioles constrict,
which increases
blood pressure
Kidneys retain
more water,
which decreases
urine output
ADH
Target tissues 1 2 3 4 5
Osmoreceptors
High blood osmotic
pressure stimulates
hypothalamic
osmoreceptors
Low blood osmotic
pressure inhibits
Nerve impulses
liberate ADH from
axon terminals in
the posterior
pituitary into
the bloodstream
activate the
neurosecretory cells
that synthesize and
release ADH
Hypothalamus
Inhibition of osmo-
receptors reduces or
stops ADH secretion
Sudoriferous
(sweat) glands
decrease water
loss by perspiration
from the skin
Arterioles constrict,
which increases
blood pressure
Kidneys retain
more water,
which decreases
urine output
ADH
Target tissues 1 2 3 4 5 6
Osmoreceptors
High blood osmotic
pressure stimulates
hypothalamic
osmoreceptors
Nerve impulses
liberate ADH from
axon terminals in
the posterior
pituitary into
the bloodstream
activate the
neurosecretory cells
that synthesize and
release ADH
Hypothalamus
Sudoriferous
(sweat) glands
decrease water
loss by perspiration
from the skin
Arterioles constrict,
which increases
blood pressure
Kidneys retain
more water,
which decreases
urine output
ADH
Target tissues 1 2 3 4
Osmoreceptors
High blood osmotic
pressure stimulates
hypothalamic
osmoreceptors
Nerve impulses
liberate ADH from
axon terminals in
the posterior
pituitary into
the bloodstream
activate the
neurosecretory cells
that synthesize and
release ADH
Hypothalamus
ADH 1 2 3
Osmoreceptors
High blood osmotic
pressure stimulates
hypothalamic
osmoreceptors 1
Osmoreceptors
High blood osmotic
pressure stimulates
hypothalamic
osmoreceptors
activate the
neurosecretory cells
that synthesize and
release ADH
Hypothalamus 1 2
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20. Thyroid Gland Located inferior to larynx 2 lobes connected by isthmus
Thyroid follicles produce thyroid hormones
Thyroxine or tetraiodothyronine (T4)
Triiodothyronine (T3)
Both increase BMR, stimulate protein synthesis, increase use of glucose and fatty acids for ATP production
Parafollicular cells or C cells produce calcitonin
Lowers blood Ca2+ by inhibiting bone resorption
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21. Thyroid Gland
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22. Thyroid Hormones Thyroid gland is located just below the larynx.
Thyroid is the largest of the pure endocrine glands.
Follicular cells secrete thyroxine.
Parafollicular cells secrete calcitonin.
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23. Production of Thyroid Hormones
Iodide (I-) actively transported into the follicle and secreted into the colloid.
Oxidized to iodine (Io).
Iodine attached to tyrosine within thyroglobulin chain.
Attachment of 1 iodine produces monoiodotyrosine (MIT).
Attachment of 2 iodines produces diiodotyrosine (DIT).
MIT and DIT or 2 DIT molecules coupled together.
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24. Production of Thyroid Hormones (continued)
T3 and T4 produced.
TSH stimulates pinocytosis into the follicular cell.
Enzymes hydrolyze T3 and T4 from thyroglobulin.
Attached to TBG and released into blood.
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25. Production of Thyroid Hormones (continued)
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26. Actions of T3 Stimulates protein synthesis.
Promotes maturation of nervous system.
Stimulates rate of cellular respiration by:
Production of uncoupling proteins.
Increase active transport by Na+/K+ pumps.
Lower cellular [ATP].
Increases metabolic heat.
Increases metabolic rate.
Stimulates increased consumption of glucose, fatty acids and other molecules.
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27. Diseases of the Thyroid
Iodine-deficiency (endemic) goiter:
Abnormal growth of the thyroid gland.
In the absence of sufficient iodine, cannot produce adequate amounts of T4 and T3.
Lack of negative feedback inhibition.
Stimulates TSH, which causes abnormal growth.
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28. Control of thyroid hormone secretion
Thyrotropin-releasing hormone (TRH) from hypothalamus
Thyroid-stimulating hormone (TSH) from anterior pituitary
Situations that increase ATP demand also increase secretion of thyroid hormones
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29. Mechanism of Thyroid Hormone Action
T4 passes into cytoplasm and is converted to T3.
Receptor proteins located in nucleus.
T3 binds to ligand-binding domain.
Other half-site is vitamin A derivative (9-cis-retinoic) acid.
DNA-binding domain can then bind to the half-site of the HRE.
Two partners can bind to the DNA to activate HRE.
Stimulate transcription of genes.
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30. Synthesis of thyroid hormones
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31. 1 2 3 4 1 2 3 5 4 1 2 3 1 2 1 T3 and T4 released into blood by
follicular cells
TRH, carried
by hypophyseal
portal veins to
anterior pituitary,
stimulates
release of TSH
by thyrotrophs
TSH released into
blood stimulates
thyroid follicular cells
Thyroid
follicle
Low blood levels of T3
and T3 or low metabolic
rate stimulate release of
Hypothalamus
Anterior
pituitary
TSH
TRH
Actions of Thyroid Hormones:
Increase basal metabolic rate
Stimulate synthesis of Na+/K+ ATPase
Increase body temperature (calorigenic effect)
Stimulate protein synthesis
Increase the use of glucose and fatty acids for ATP production
Stimulate lipolysis
Enhance some actions of catecholamines
Regulate development and growth of nervous tissue and bones 1 2 3 4
T3 and T4
released into
blood by
follicular cells
Elevated
T3inhibits
release of
TRH and
TSH
(negative
feedback)
TRH, carried
by hypophyseal
portal veins to
anterior pituitary,
stimulates
release of TSH
by thyrotrophs
TSH released into
blood stimulates
thyroid follicular cells
Thyroid
follicle
Low blood levels of T3
and T3 or low metabolic
rate stimulate release of
Hypothalamus
Anterior
pituitary
TRH
Actions of Thyroid Hormones:
Increase basal metabolic rate
Stimulate synthesis of Na+/K+ ATPase
Increase body temperature (calorigenic effect)
Stimulate protein synthesis
Increase the use of glucose and fatty acids for ATP production
Stimulate lipolysis
Enhance some actions of catecholamines
Regulate development and growth of nervous tissue and bones 1 2 3 5 4
TRH, carried
by hypophyseal
portal veins to
anterior pituitary,
stimulates
release of TSH
by thyrotrophs
TSH released into
blood stimulates
thyroid follicular cells
Thyroid
follicle
Low blood levels of T3
and T3 or low metabolic
rate stimulate release of
Hypothalamus
Anterior
pituitary
TSH
TRH
Actions of Thyroid Hormones:
Increase basal metabolic rate
Stimulate synthesis of Na+/K+ ATPase
Increase body temperature (calorigenic effect)
Stimulate protein synthesis
Increase the use of glucose and fatty acids for ATP production
Stimulate lipolysis
Enhance some actions of catecholamines
Regulate development and growth of nervous tissue and bones 1 2 3
TRH, carried
by hypophyseal
portal veins to
anterior pituitary,
stimulates
release of TSH
by thyrotrophs
Low blood levels of T3
and T3 or low metabolic
rate stimulate release of
Hypothalamus
TSH
TRH
Actions of Thyroid Hormones:
Increase basal metabolic rate
Stimulate synthesis of Na+/K+ ATPase
Increase body temperature (calorigenic effect)
Stimulate protein synthesis
Increase the use of glucose and fatty acids for ATP production
Stimulate lipolysis
Enhance some actions of catecholamines
Regulate development and growth of nervous tissue and bones 1 2
Anterior
pituitary
Low blood levels of T3
and T3 or low metabolic
rate stimulate release of
Hypothalamus
TRH
Actions of Thyroid Hormones:
Increase basal metabolic rate
Stimulate synthesis of Na+/K+ ATPase
Increase body temperature (calorigenic effect)
Stimulate protein synthesis
Increase the use of glucose and fatty acids for ATP production
Stimulate lipolysis
Enhance some actions of catecholamines
Regulate development and growth of nervous tissue and bones 1
Anterior
pituitary
University of Jordan

32. Thank You
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