HYPOTHALAMUS AND PITUITARY

• Hypothalamus


  Portion of the brain located on the walls and floors of the 3rd ventricle

  
• Hypothalamus

  • Located above the pituitary gland
  • Connected to the pituitary gland by infundibulum
• Zones of Hypothalamus

  • Periventricular Zone/Nuclei
  • Medial Zone/Nuclei
  • Lateral Zone/Nuclei
• Periventricular Zone/Nuclei


  Regulates hormone levels and other messages carried in the blood
• Medial Zone/Nuclei

  Responsible for the autonomic behavior
• Lateral Zone/Nuclei

  Responsible for the somatic behavior
• Hypothalamic-releasing Hormones

  • Corticotropin-Releasing Hormone (CRH)
  • Thyrotropin RH
  • Growth Hormone RH
  • Gonadotropin RH (GnRH)
  • Prolactin Releasing Factor (PRF / PRH)
• Corticotropin-Releasing Hormone (CRH)


  Stimulates the secretion of ACTH
• Thyrotropin RH

  Stimulates the secretion of TSH & PRL
• Growth Hormone RH

  Stimulates the secretion of GH
• Gonadotropin RH (GnRH)

  Stimulates the secretion of FSH & LH
• Prolactin Releasing Factor (PRF / PRH)

  Stimulates the secretion of PRL
• Somatostatin

  Inhibits the release of growth hormone
• Hypothalamic-inhibiting Hormone

  • Growth Hormone Inhibiting Hormone (GHIH) e.g. Somatostatin
  • Prolactin Inhibiting Factor (PIF) e.g. Dopamine
• • tropic


  Hormone which acts, turning towards a certain tissue/organ
• • trophic


  Hormone which acts on the enhancement of neural growth
• Pituitary Gland

  Also known as 'Hypophysis'
• Pituitary Gland

  • Located in the Sella Turcica (below the hypothalamus)
  • Anterior Pituitary Gland (Adenohypophysis) possesses 5 distinct hormones which are synthesized and secreted
  • Posterior Pituitary Gland (Neurohypophysis) unable to synthesize hormones, promotes the secretion of hormones
• Vasopressin (ADH / AVP)

  Hormone secreted by the posterior pituitary gland
• Oxytocin

  Hormone secreted by the posterior pituitary gland
• ADH and Oxytocin are synthesized by the neurons of the paraventricular nuclei and supraoptic nuclei of the hypothalamus
• Anterior Pituitary Gland (APT)

  • Hypothalamus communicates with the APT by secreting its own set of trophic hormones that are specific for each of the cell population
  • It is a TRUE endocrine gland, capable of synthesizing and secreting hormones
• Growth Hormone (GH)

  • A single chain polypeptide of 191 amino acid, synthesized by Somatotroph Cells of the APT in response to GHRH from the hypothalamus
  • Structurally similar to PRL and Human Placental Lactogen
• Growth Hormone (GH)Functions

  • Promotes growth
  • Increases lipolysis
  • Increases hepatic glucose production and decreases tissue glucose uptake
  • Increases protein synthesis
• GH Secretion

  • Secreted in pulsatile fashion
  • Peaks during puberty, steady decline with increasing age
  • Increased during the first 2 hours of deep sleep, Rapid Eye Movement (REM) sleep
  • Mediated by GHRH (promotes release) and Somatostatin (inhibits release)
  • Can be stimulated by stress, surgery, sepsis, exercise, hypoglycemia, fasting, high protein meals
• Females have higher GH secretion than males


  Due to gynecologic hormone Estrogen, which sensitizes the hypothalamus to release GHRH
• Causes of GH Deficiency (Hypopituitarism)

  • Idiopathic GH Deficiency
  • Pituitary Adenoma (Tumor in Pituitary)
• Dwarfism


  Generalized deficiency of APT secretion during childhood, with all physical parts developing in appropriate proportion
• Types of Dwarfism

  • Pituitary Dwarfism (Levi-Lorain Dwarf)
  • African Pygmy
• Treatment for Dwarfism

  • Human GH synthesized from E.coli using Recombinant DNA Technology, safer and less risky than GH derived from humans
  • Human-derived GH --- can transmit disease (Creutzfelt-Jakob disease)
• Gigantism


  Large quantities of GH are produced, leading to rapid growth of all body tissues including bones
• Acromegaly

  Person cannot grow any taller but the bones become thicker and soft tissues continue to grow, with marked enlargement in bones of the hands and feet
• Specimen Requirements for GH Measurement

  Fasting and 30 minutes of complete rest prior to blood collection
• Chemiluminescent Immunoassay


  Most common method for GH measurement
• Tests for Growth Hormone Deficiency (GHD)

  • Insulin Tolerance Test (ITT)
  • IGF-1 Measurement
  • Arginine Stimulation Test
• Insulin Tolerance Test (ITT)


  Gold standard in measuring GHD
• IGF-1 Measurement


  Screening for GHD among children, also declined in malnutrition, uncontrolled DM, age, hypothyroidism, hepatic disease
• Tests for GH Excess

  • Screening Test for Acromegaly (Randomly collected IGF-1)
  • Confirmatory Test for Acromegaly (OGTT)
  • GH Suppression Test
• OGTT for Acromegaly

  Determines if the cell could take up glucose that is administered, GH secretion remains high despite the inhibition in GH excess
• Other conditions that cause elevated GH secretion

  • Malnutrition
  • Renal Disease
  • Cirrhosis
  • Physical and emotional stress