Hypothalamus and Pituitary

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Hypothalamus and Pituitary
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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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HYPOTHALAMUS AND ANTERIORPITUITARY LOBE

• The hypothalamic hormones either promote or
  inhibit release of the anterior pituitary
  hormones

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Endocrine Control Three Levels of Integration
Figure 7-13 Hormones of the hypothalamic-anterior
pituitary pathway
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Characteristics of hypothalamic releasing
hormones

• Secretion in pulses
• Act on specific membrane receptors
• Transduce signals via second messengers
• Stimulate release of stored pituitary hormones
• Stimulate synthesis of pituitary hormones
• Stimulates hyperplasia and hypertophy of target
  cells

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• HORMONES AND THE
• HYPOTHALAMUS
• The hypothalamus is the major regulatory area for
  the
• internal environment, acting as an interface
  between
• the two control systems, the nervous system and
  the
• endocrine system. As well as controlling the
  activities of
• the autonomic nervous system.
• It produces a large number of Releasing hormones
  involved directly or indirectly in
• maintenance of homeostasis
• management of stress, i.e. disturbance of
  Homeostasis
• determination of the size, shape and sexual
  characteristics of the body morphogenesis.

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• NEURAL CONNECTIONS
• The hypothalamus receives information from many
  parts of the nervous system. These include
• receptor cells which monitor many aspects of
  the bodys internal environment
• pressures in the circulation
• osmotic pressure and the state of the bodys
  fluid balance
• composition of the body fluids, e.g. pH,
  electrolytes,
• glucose
• body temperature
• regulation of food intake.

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Hypothalamic releasing hormones
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Hypothalamus and pituitary gland
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Anterior pituitary

• Anterior pituitary connected to the hypothalamus
  by hypothalmoanterior pituitary portal vessels.
• The anterior pituitary produces six peptide
  hormones
• prolactin,
• growth hormone (GH),
• thyroid stimulating hormone (TSH),
• adrenocorticotropic hormone (ACTH),
• follicle-stimulating hormone (FSH),
• luteinizing hormone (LH).

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Anterior pituitary cells and hormones
Cell type Product Target
Corticotroph ACTHMSH Adrenal gland Adipocytes Melanocytes
Thyrotroph TSH Thyroid gland
Gonadotroph LH, FSH Gonads
Somatotroph GH All tissues, liver
Lactotroph PRL Breasts gonads
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ANTERIOR PITUITARY
SECRETES TROPIC HORMONES IN PULSATILE FASHION
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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
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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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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Figure 7-12 Synthesis, storage, and release of
posterior pituitary hormones
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POSTERIOR PITUITARY
Oxytocin Synthesized as the precursor hormone
prepro-oxyphysin Action primarily on the
breasts and uterus
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POSTERIOR PITUITARY
Vasopressin or Antidiuritic Hormone Plasma
osmolality is monitored by osmoreceptors in the
hypothalamus Increases in plasma osmolality
stimulates secretion of vasopressin Small
changes above normal plasma osmotic pressure (
285 mosm/kg) stimulate release of vasopressin
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Physiologic Effects of Antidiuretic Hormone

• Effects on the Kidney
• The single most important effect of Antidiuretic
  hormone is to conserve body water by reducing the
  output of urine.
• Injection of small amounts of Antidiuretic
  hormone into a person or animal results in
  Antidiuresis or decreased formation of urine, and
  the hormone was named for this effect.
• A diuretic is an agent that increases the rate of
  urine formation.

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Facultative water reabsorption
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The Effects of ADH on the DCT and Collecting Ducts
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• Antidiuretic hormone binds to receptors in the
  distal or collecting tubules of the kidney and
  promotes reabsorbtion of water back into the
  circulation.
• In the absence of Antidiuretic hormone, the
  kidney tubules are virtually impermeable to
  water, and it flows out as urine.

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Control of Antidiuretic Hormone Secretion

• The most important variable regulating
  Antidiuretic hormone secretion is plasma
  osmolarity, or the concentration of solutes in
  blood.
• Osmolarity is sensed in the hypothalamus by
  neurons known as an osmoreceptors, and those
  neurons, in turn, simulate secretion from the
  neurons that produce Antidiuretic hormone.
• When plasma osmolarity is below a certain
  threshold, the osmoreceptors are not activated
  and Antidiuretic hormone secretion is suppressed

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• Secretion of antidiuretic hormone is also
  simulated by decreases in blood pressure and
  volume, conditions sensed by stretch receptors in
  the heart and large arteries.
• Changes in blood pressure and volume are not
  nearly as sensitive a stimulator as increased
  osmolarity, but are nonetheless potent in severe
  conditions.
• For example, Loss of 15 or 20 of blood volume
  by hemorrhage results in massive secretion of
  Antidiuretic hormone.

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Disease States

• The most common disease of man and animals
  related to Antidiuretic hormone is diabetes
  insipidus
• Hypothalamic ("central") diabetes insipidus
  results from a deficiency in secretion of
  antidiuretic hormone from the posterior
  pituitary.
• Nephrogenic diabetes insipidus occurs when the
  kidney is unable to respond to antidiuretic
  hormone.

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• The major sign of either type of diabetes
  insipidus is excessive urine production.

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PATHOPHYSIOLOGICAL CHANGES IN ADH SECRETION

• Effects of Primary Polydipsia, Diabetes
  
• Insipidus and SIADH

Primary Polydipsia Central NeurogenicDiabetes Insipidus SIADH
1. Permeability of collecting ducts to H2O
2. Urine flow
3. Urine osmolarity
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4. ECF volume
5. ECF osmolarity (Na concentration)
6. ICF volume
7. ICF osmolarity