NSC%205404%20:%20Session%201%20Hypothalamus%20and%20its%20regulation%20of%20anterior%20and%20posterior%20pituitary%20secretions

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NSC 5404 Session 1Hypothalamus and its
regulation of anterior and posterior pituitary
secretions

• Leo Renaud, MD PhD
• Professor, Medicine Neurology,
• University of Ottawa
• Associate Director Senior Scientist, OHRI

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Pituitary and Hypothalamus
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Where what is the hypothalamus?
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Some developmental notes Anterior pituitary
(adenohypophysis) forms from the roof of the
pharynx in the embryo. Posterior pituitary
develops from the floor of the third ventricle
forming the stalk (infundibulum) and the
posterior pituitary (neurohypophysis). Anterior
pituitary has no neurons or synapses, just
cells producing hormones such as growth hormone,
leuteinizing hormone, follicle stimulating
hormone, thyroid stimulating hormone,
adrenocorticotropic hormone. Infundibulum
contains axons from hypothalamic neurons that
project into the posterior pituitary where they
terminate near capillaries. These terminals
contain hormones oxytocin and vasopressin.
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Introduction to the Pituitary and
Hypothalamus Pituitary and hypothalamus utilize
synaptic communication as well as hormonal
communication to regulate target cells. Pituitary
and hypothalamus are the link between the nervous
system and the endocrine system. Hypothalamus
is also major regulator of body homeostasis 1.
Homeostatic control includes regulating hunger,
thirst, sex drive, sleep-wake cycles, body
temperature, blood glucose. 2. Endocrine control
via regulating the release of pituitary
hormones. 3. Autonomic control via descending
pathways to sympathetic and parasympathetic
preganglionic neurons. 4. Limbic function via
connections to limbic system regulating
emotional behavior.
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Functions of Selected Regions of
Hypothalamus Suprachiasmatic nucleus THE
biological clock, regulates circadian
rhythms. Lateral hypothalamus feeding and
arousal (orexinergic cells). Ventromedial
nucleus a satiety center, inhibits
hunger. Anterior hypothalamus contains
osmoreceptors, triggers thirst Thermoregulation
involves several systems including sweat glands,
vasodilation/vasoconstriction, skeletal muscles
involved in shivering and panting, and endocrine
systems that control metabolic rate. Preoptic
area (POA) detects increased body temp and
activates systems that dissipate heat lesions
here cause hyperthermia. Posterior HT functions
to conserve heat lesions here cause poikilother
mia, where body temp matches environment
temp. More recent studies suggest HT functions in
sexual desire/sex preference.
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A global view of hypothalamic pituitary
functions
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Hypothalamus regulator of the endocrine system
Figure 18.1
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Three Methods of Hypothalamic Control over the
Endocrine System
Figure 18.5
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Anatomy of the pituitary gland
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Anatomy and Orientation of the Pituitary Gland
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The Hypophyseal Portal System
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Hypothalamic Control of the Anterior Pituitary

• Hormonal control mechanism
• Hypothalamic neurons synthesize releasing and
  inhibiting peptide hormones.
• These are transported to axon endings in the
  median eminence where they are secreted into the
  hypothalamo-hypophyseal portal system to reach
  receptors that regulate the secretions of
  anterior pituitary hormones

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How does the neuroendocrine axis work?

• Hypothalamic parvicellular neurons synthesize
  release- or release-inhibiting factors or
  hormones (peptides)
• Packaged in secretory granules, transported in
  axons to nerve terminal storage sites
• On demand, neurons depolarize, prompting
  frequency-dependent exocytosis into the median
  eminence capillaries of the pituitary portal
  vessels
• Transported as hormones to the anterior
  pituitary where they exit to the extracellular
  space
• Attach to specific G-protein coupled receptors on
  target cells, triggering exocytosis of
  appropriate hormones that seek their peripheral
  glandular targets

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Anterior Pituitary
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Thyroid-Releasing Hormone
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The anterior pituitary is actually a glandular
structure, composed of diverse cell types that
synthesize specific hormones to control specific
peripheral glands or tissues ?luteinizing
hormone (LH) and follicle stimulating hormone
(FSH) that regulate ovarian function ?thyroid
stimulating hormone (TSH) to regulate thyroid
function ?adrenocorticotrophic hormone (ACTH)
to regulate adrenal cortex function ?growth
hormone (GH) for bone and muscle ?prolactin to
stimulate milk production in the breast.
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Adenohypophysis LM histology
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Adenohypophysis EM histology
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GnRH
GONADOTROPIC CELL
B
Gq
GnRH receptor
?q
PLC
?q
Ca2
DAG
Protein kinase C
PIP2
IP3
Y
Ca2
SER
Protein phosphorylation
Ca2
Figure 6. In the gonadotropes GnRH causes release
of LH and FSH (B)
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Feedback control of Endocrine Secretion
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Feedback control of Endocrine Secretion
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Some clinical conditions that may arise due to
altered feedback or lack of hormone regulation

• Too much / too little thyroxine (T4) and
  tri-iodothyronine (T3) results in hyper /
  hypothyroidism respectively
• To much growth hormone secretion causes a
  condition called acromegaly
• Excessive adrenal glucocorticoid secretion can
  produce Cushings syndrome

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Symptoms of excess circulating thyroid hormones
thyroxine (T4) and triiodothyronine (T3)fine
tremor, heat intolerance, sweaty skin,
exophthalmos, possible thyroid enlargement
(goitre).
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Excess Growth Hormone secretion ? Acromegaly
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Clinical features of excessive secretion of
cortisol

• Truncal obesity
• Moon facies
• Abdominal striae
• Osteoporosis
• Acne
• Easy bruising
• Hirsutism
• Hypertension
• Hyperglycemia

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