INTRODUCTION TO THE ENDOCRINE SYSTEM AND THE PITUITARY-HYPOTHALAMIC AXIS

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INTRODUCTION TO THE ENDOCRINE SYSTEM AND THE
PITUITARY-HYPOTHALAMIC AXIS

• D. C. MIKULECKY
• PROFESSOR OF PHYSIOLOGY

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COMPARISON OF ENDOCRINE AND NERVOUS SYSTEMS

• NERVOUS SYSTEM
• WIRED
• CHEMICAL SIGNAL AT TARGET CELL
• RAPID
• BRIEF DURATION

• ENDOCRINE SYSTEM
• WIRELESS
• CHEMICAL SIGNAL AT TARGET CELL
• SLOW
• LONG DURATION

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CATEGORIES OF HORMONES

• PEPTIDES
• AMINES
• STEROIDS

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PEPTIDES

• HYDROPHILIC
• DISSOLVED IN PLASMA
• RECEPTOR ON CELL SURFACE
• SECOND MESSENGERS
• MAY ACTIVATE SPECIFIC GENES TO REGULATE PROTEIN
  SYNTHESIS

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PEPTIDE HORMONES

• HYPOTHALAMIC
• PITUITARY
• PANREATIC
• PARATHYROID
• GI
• KIDNEY
• LIVER
• HEART

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AMINES

• THYROID HORMONE
• CATECHOLAMINES
• ALL DERIVED FROM AMINO ACID TYROSINE
• UNIQUE SYNTHETIC AND SECRETORY PATHWAYS

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STEROIDS

• DERIVED FROM CHOLESTEROL
• LIPOPHILIC
• RECEPTOR IN CYTOPLASM
• MAY ACTIVATE SPECIFIC GENES TO INITIATE PROTEIN
  SYNTHESIS
• ADRENAL CORTICAL
• GONADAL
• PLACENTAL

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PLASMA CONCENTRATION OF HORMONES

• DEPENDS ON RATE OF SECRETION
• NEGATIVE FEEDBACK
• NEUROENDOCRINE REFLEXES
• DIURNAL RHYTHMS

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TYPES OF ENDOCRINE DISORDERS

• HORMONE EXCESS
• HORMONE DEFICIENCY
• DECREASED RESPOSIVENESS OF RECEPTORS

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THE PITUITARY- HYPOTHALAMIC AXIS

• INTERFACING THE NERVOUS SYSTEM WITH THE ENDOCRINE
  SYSTEM

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HYPOTHALAMUS AND POSTERIOR PITUITARY
NEUROSECRETORY NEURONS
HYPOTHALAMUS
VASOPRESSIN
POSTERIOR PITUITARY
OXYTOCIN
ANTERIOR PITUITARY
SYSTEMIC ARTERY
SYSTEMIC VEIN
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HYPOTHALAMUS AND ANTERIOR PITUITARY
NEUROSECRETORY NEURONS
HYPOTHALAMUS

• ANTERIOR
• PITUITARY
• TSH
• ACTH
• PROLACTIN
• GROWTH
• HORMONE
• LH
• FSH

POSTERIOR PITUITARY
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CLASSIFICATION OF ANTERIOR PITUITARY HORMONES

• GLYCOPROTEIN FAMILY TSH, FSH,LH
• GROWTH HORMONE PROLACTIN FAMILY GH OR STH
• PROOPIOMELANOCORIN FAMILY ACTH, ?-LIPOTROPIN,
  ?-ENDORPHIN

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HYPOTHALAMIC-HYPOPHYSEAL PORTAL SYSTEM

• SECRETED BY NERVE CELLS IN HYPOTHALAMUS
• VESSELS PASS THROUGH STALK OF PITUITARY FROM
  HYPOTHALAMUS TO ANTERIOR PITUITARY
• CARRY HYPOTHALAMIC REGULATORY HORMONES

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HYPOTHALAMIC REGULATORY HORMONES

• HYPOPHYSIOTROPIC HORMONES
• CONTROL THE SECRETION OF OTHER HORMONES BY ACTING
  ON ENDOCRINE TISSUE

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HYPOTHALAMIC RELEASING AND INHIBITING HORMONES
(HYPOPHYSIOTROPIC)

• CONTROL THE SECRETION OF ANTERIOR PITUITARY
  TROPIC HORMONES
• TRHTHYROTROPIN-RELEASING HORMONE
• PRFPROLACTIN RELEASING FACTOR
• PIFPROLACTIN INHIBITING FACTOR
• GHRHGROWTH HORMONE RELEASING HORMONE
• SRIF SOMATOTROPIN RELEASE-INHIBITING FACTOR
• CRHCORTICOTROPHIN RELEASING HORMONE
• GnRH GONADOTROPIN RELEASING HORMONE

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HIERARCHICAL CONTROL
INPUT
HYPOTHALAMUS
HORMONE 1 (RELEASING/INHIBITING)
H/H PORTAL SYSTEM
ANTERIOR PITUITARY
HORMONE 2 (TROPIC)
SYSTEMIC CIRCULATION
ENDOCRINE GLAND
HORMONE 3
SYSTEMIC CIRCULATION
TARGET CELLS
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NEGATIVE FEEDBACK
INPUT
HYPOTHALAMUS
HORMONE 1 (RELEASING/INHIBITING)
H/H PORTAL SYSTEM
ANTERIOR PITUITARY
HORMONE 2 (TROPIC)
SYSTEMIC CIRCULATION
ENDOCRINE GLAND
HORMONE 3
SYSTEMIC CIRCULATION
TARGET CELLS
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ANTERIOR PITUITARY HORMONESTSH

• THYROID GLAND
• THYROID HORMONES (T3 T4 )

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ANTERIOR PITUITARY HORMONESACTH

• ADRENAL CORTEX
• CORTISOL

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ANTERIOR PITUITARY HORMONESPROLACTIN

• MAMMARY GLANDS
• BREAST GROWTH AND MILK SECRETION

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ANTERIOR PITUITARY HORMONES GROWTH HORMONE

• LIVER
• SOMATOMEDINS
• BONE
• SOFT TISSUE
• GROWTH

• MANY TISSUES
• INTERMEDIARY METABOLISM
• INCREASE OR DECREASE

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ANTERIOR PITUITARY HORMONESLH FSH ACT ON
GONADS

• LHLUTEINIZING HORMONE
• SEX HORMONE SECRETION
• F ESTROGEN AND PROGESTERONE
• M TESTOSTERONE

• FSHFOLLICLE STIMULATING HORMONE
• GAMETE PRODUCTION
• OVA
• SPERM