Hypothalamus

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Hypothalamus Pituitary

• Felix E. Grissom, Ph.D.
• Department of Physiology Biophysics
• 2219 Adams Building
• Tel [phone]

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Figure 11-3 Autonomic control centers in the
brain
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Hypothalamus

• Integrates functions that maintain chemical and
  temperature homeostasis
• Functions with the limbic system
• Controls the release of hormones from the
  anterior and posterior pituitary

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Hypothalamus

• Synthesizes releasing hormones in cell bodies of
  neurons
• Hormones are transported down the axon and stored
  in the nerve endings
• Hormones are released in pulses

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Hypothalamic Releasing Hormones

• Seven releasing hormones are made in the
  hypothalamus
• Thyrotropin-releasing hormone (TRH)
• Corticotropin-releasing hormone (CRH)
• Gonadotropin-releasing hormone (GnRH)
• Growth hormone-releasing hormone (GHRH)
• Growth hormone-release inhibiting hormone (GHIH)
• Prolactin-releasing factor (PRF)
• Prolactin-inhibiting hormone (PIH)

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Hypothalamus Releasing Hormones Secretion

• Is influenced by emotions
• Can be influenced by the metabolic state of the
  individual
• Delivered to the anterior pituitary via the
  hypothalamic-hypophyseal portal system
• Usually initiates a three-hormone sequence

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Anterior Pituitary
Is also called the Adenohypophysis Secretes
tropic hormones in a pulsatile fashion Synthesize
s various hormones in various specific cell
populations
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Anterior Pituitary Hormones
Each of anterior pituitary hormone is
synthesized by a cell population. Corticotropes
- ACTH Lactotropes -
Prolactin Somatotropes -
GH Thyrotropes - Thyrotropin Gonadot
ropes - FSH, LH
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Anterior Pituitary Hormones
Growth Hormone (GH, Somatotropin) primary
hormone responsible for regulating body growth,
and is important in metabolism Thyroid-stimulatin
g Hormone (TSH) stimulates secretion of thyroid
hormone growth of thyroid gland Adrenocorticotr
opic Hormone (ACTH) stimulates cortisol
secretion by the adrenal cortex promotes growth
of adrenal cortex
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Anterior Pituitary Hormones
Follicle-stimulating Hormone (FSH) Females
stimulates growth development of ovarian
follicles, promotes secretion of estrogen by
ovaries. Males required for sperm
production Luteinizing Hormone (LH) Females
responsible for ovulation, formation of corpus
luteum in the ovary, and regulation of ovarian
secretion of female sex hormones. Males
stimulates cell in the testes to secrete
testosterone Prolactin Females stimulates
breast development and milk production. Males
involved in testicular function
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Growth Hormone Activity
Increases plasma free fatty acids (FFA) - source
of energy for muscle tissue Increases hepatic
glucose output Decreases insulin sensitivity in
muscle Is protein anabolic hormone
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Growth Hormone Activity
Exerts its growth-promoting through interactions
mainly induction of Insulin-like Growth Factor
I (IGF-I). IGF-I synthesis is stimulated by
GH Major source of IGF-I is the liver IGF-I is
also locally produced in other tissues
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Endocrine Control Three Levels of Integration

• Hypothalamic stimulationfrom CNS
• Pituitary stimulationfrom hypothalamic trophic
  Hs
• Endocrine gland stimulationfrom pituitary
  trophic Hs

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Endocrine Control Three Levels of Integration
Figure 7-13 Hormones of the hypothalamic-anterior
pituitary pathway
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Multiple Stimuli for Hormone Release Nervous
Endocrine

• Stimuli
• Stretch
• Glucose
• Insulin levels
• Reflex
• Lower blood glucose
• Reduces stimulus
• Reduces insulin release

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Multiple Hormones Can Target a Cell/Tissue

• Growth Hormone
• Somatomedins
• Thyroxin
• All have receptors on many tissues
• Stimulate pathways for growth

Figure 7-17 A complex endocrine pathway
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More Impacts on Target Cells

• Synergism multiple stimuli more than additive
• Cortisol 5
• Glucagon 10
• Epinephrine 20 (added 35)
• Synergistic effect 140
• Antagonism glucagons opposes insulin
• Permissiveness need 2nd hormone to get full
  expression

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More Impacts on Target Cells
Figure 7-18 Synergism
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Posterior Pituitary
Comprised of the endings of axons from cell
bodies in the hypothalamus (supraoptic and
paraventricular) Axons pass from the
hypothalamus to the posterior pituitary via the
hypothalamohypophysial tract Posterior pituitary
hormones are synthesized in the cell bodies of
neurons in the supraoptic and paraventricular
nuclei
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Posterior Pituitary
Hormones synthesized in the hypothalamus are
transported down the axons to the endings in the
posterior pituitary Hormones are stored in
vesicles in the posterior pituitary until release
into the circulation Principal Hormones
Vasopressin Oxytocin
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Secretion of Posterior Pituitary Hormones
Figure 7-12 Synthesis, storage, and release of
posterior pituitary hormones
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Oxytocin
Is synthesized as the precursor hormone
prepro-oxyphysin Acts primarily on the mammary
gland and uterus Increases contraction of
smooth muscle of the vas deferens
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Oxytocin
Secretion is increased during labor May also act
to facilitate sperm transport in uterus
(non-pregnancy state)
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Posterior Pituitary Regulation of Osmolality
Plasma osmolality is monitored by osmoreceptors
in the hypothalamus Increases in plasma
osmolality stimulates secretion of
vasopressin Small changes above the normal
plasma osmotic pressure (285 mosm/kg) stimulate
release of vasopressin
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Vasopressin (ADH)
Is also known as antiduretic hormone (ADH)
Participates in body water regulation (Water is
lost from lungs, sweat, feces and urine on a
daily basis)
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Osmolality

• Refers to the amount of solutes in a solution
• Loss or gain of water without solutes (free
  water
• gain or loss) changes the osmolality of ECF
• Must be regulated to maintain normal cell
  activity

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Vasopressin (ADH) Secretion
Secretion is Stimulated by 1. Large decreases in
blood volume 2. Decreases in blood
pressure 3. Pain, fear, trauma, and stress
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Vasopressin Activity
Decreases water excretion by kidneys (V2
receptors) Constricts blood vessels (V1
receptors)- arteriolar smooth muscle Increases
adrenocorticortropin hormone (V1B receptors)
secretion from the anterior pituitary
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Negative Feedback Controls Long Short Loop
Reflexes
Figure 7-14 Negative feedback loops in the
hypothalamic-anterior pituitary pathway
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Negative Feedback Controls Long Short Loop
Reflexes
Figure 7-15 Control pathway for cortisol
secretion
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Pathologies Over or Under Production

• "no bad hormones just too much or too little"
• Exogenous medication
• Replaces exceeds normal
• Cause atrophy of gland
• Hypersecretion too much
• Tumors or cancer
• Grave's disease- thyroxin
• Hyposecretion too little
• Goiter thyroxin
• Diabetes insulin

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Pathologies Over or Under Production
Figure 7-19 Negative feedback by exogenous
cortisol
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Pathologies Due to Receptors

• Downregulation hyperinsulinemia
• Transduction abnormalities
• Testicular feminization syndrome
• Pseudohypothyroidism
• Abnormalities of control mechanisms

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Pathologies Due to Receptors
Figure 7-20 Primary and secondary hypersecretion
of cortisol